How Long Is a Cow Used for the Milking Process Before She Needs to Get Pregnant Again
Efficient and profitable reproductive performance of a dairy herd requires routine but conscientious heat detection and proper timing of artificial insemination. Failure to detect estrus (heat) is a major factor contributing to low fertility. Approximately one-half of the heats are undetected on dairy farms in the United States. In improver, inquiry based on levels of the hormone progesterone in milk shows that up to fifteen percent of the cattle presented for insemination are not in oestrus. Failure to notice cows that are in heat and breeding cows non in heat result in economic loss for the producer considering of extended calving intervals and additional semen expense. If a herd producing 16,000 pounds of milk per year and maintaining a 12.5 calendar month calving interval is compared with the same herd maintaining a xiii.5 month calving interval, the loss in potential milk solitary is between $35 and $45 per cow per twelvemonth, depending on milk price and feed costs. Therefore, poor heat detection is plush to the producer and should be considered the disquisitional component of reproductive management.
Efficient heat detection and timely insemination also are important to beef producers who use artificial insemination. Failure to discover heat early in the breeding season or improper timing of insemination due to heat detection errors results in extended calving intervals and additional semen expense.
This publication provides data on characteristics of the estrous cycle, signs of heat and estrous behavior, factors affecting expression of rut, and management suggestions for improving rut detection. Various ways to monitor the efficiency of heat detection and several heat detection aids also are described.
Characteristics of the Estrous Cycle
In general, at that place are ii structures that tin be found on the ovary, the corpus luteum and follicles of diverse sizes. It was thought that several follicles developed big fluid cavities (antrum) toward the end of the bicycle or prior to the first postpartum heat but that only ane or two follicles were dominant and ovulated, releasing the oocyte (egg) shortly after heat. The other follicles were thought to degenerate and a corpus luteum to develop at the site of ovulation. Recent studies, however, reveal dissimilar changes in growth and degeneration of follicles during the cycle.
Using real-time ultrasound technology to monitor ovarian structures on a daily basis, several independent enquiry groups have shown that cows or heifers may have two, three, or iv groups of follicles that develop during each estrous cycle. Usually, a single follicle within each group becomes dominant, suppressing the continued growth of the other follicles within that group. Such groups of developing follicles are chosen "waves" of follicular growth. Thus various populations of small, medium, and large follicles are nowadays on the ovary each twenty-four hours of the cycle.
On about day 18 of a normal 21-day cycle, the corpus luteum (CL) that adult afterwards the previous ovulation begins to regress and progesterone concentrations refuse. The dominant follicle of this last wave continues to increase in size and produces the hormone estrogen. Since progesterone concentrations are low, estrogen causes the characteristic signs and behavior associated with estrus. At the offset of standing heat, estrogen also initiates the release of a surge of luteinizing hormone (LH) from the anterior pituitary gland in the brain.
Luteinizing hormone begins the process of ovulation, which occurs approximately 25 to 32 hours after the onset of standing heat. At the site of ovulation, the new CL increases in size and gradually produces increasing amounts of progesterone. Concentrations of progesterone in the claret remain loftier from about day 6 through day 18 of the cycle. Although follicles proceed to develop and fifty-fifty produce estrogen (estrogen-agile follicles) during midcycle, the high level of progesterone prevents their last maturation and inhibits expression of heat. Eventually these larger follicles degenerate and estrogen product declines.
Progesterone too prepares the uterus for pregnancy, inhibits uterine contractions, and maintains pregnancy. The CL regresses in cows that fail to become significant and progesterone levels refuse, the dominant follicle completes development, and the cow returns to estrus, initiating a new cycle. If pregnancy occurs, the CL does not regress and progesterone levels remain elevated throughout pregnancy.
Thus the estrous bicycle can be divided into 4 periods: proestrus, heat, metestrus, and diestrus. Proestrus is the period when progesterone declines with regression of the CL, estrogen increases, and secondary signs of estrus begin to occur. Heat is characterized past standing behavior (truthful heat). Metestrus begins immediately after estrus when ovulation and early development of the CL occur, a catamenia that lasts three to five days. Finally, diestrus is the time when the CL is functional, the longest phase of the estrous bicycle.
Figure 1 illustrates the structural changes on the ovaries and the hormone concentrations during an estrous wheel with three waves of follicular development. Although specific days of the bicycle are indicated on the diagram, this is for illustration purposes only since in that location is variation among cows.
Figure one. Changes in ovarian structures and hormone concentrations during the estrous bike. For simplicity, only one ovary is illustrated; however, structural changes are occurring on both ovaries. Specific days of the wheel are listed for analogy only. At that place is variation among cows.
Signs of Heat
Continuing and mounting activity.
Primary sign
A cow continuing to be mounted is the almost accurate sign of rut. Standing heat is the most sexually intensive period of the estrous bicycle. During this menstruation, cows stand up to exist mounted by other cows or move forrard slightly with the weight of the mounting cow. Cows that move away quickly when a mount is attempted are non in true oestrus. In gild for continuing behavior to exist expressed, cattle obviously must be allowed to interact.
The expression of estrus is due to the elevated level of estrogen in the blood when progesterone is very low. Occasionally cows in early pregnancy, approaching the cease of pregnancy, or with ovarian follicular cysts have like hormonal relationships and may express signs of heat.
The boilerplate duration of standing heat is 15 to 18 hours, but heat duration may vary from 8 to 30 hours amongst cows. An estrous cow ordinarily stands to be mounted xx to 55 times during her estrous menses. Each mountain lasts three to seven seconds. Factors that affect expression of rut are discussed in a later section.
Secondary signs
Secondary signs vary in duration and intensity. These signs may occur earlier, during, or afterwards continuing heat and are not related to time of ovulation. Dairy producers should use these signs as clues or scout the specific cow more closely for standing behavior. To decide whether cows exhibiting secondary signs volition stand to exist mounted, they may be isolated with a sexually active cow or teaser animal.
Mounting Other Cows
Cattle that exhibit this behavior may be in estrus or budgeted oestrus. Mounting activity is performed much less often past cows in midcycle. Although mounting cannot be used as a true chief sign of heat, cows exhibiting such behavior should be watched closely for standing behavior.
Fungus Belch
As an indirect issue of elevated estrogen levels, fungus is produced in the cervix and accumulates with other fluids in the vagina earlier, during, and shortly later on estrus. Long viscous, clear elastic strands of mucus more often than not hang from the vulva. Sometimes, however, the fungus does not announced externally until the moo-cow is palpated during insemination and the mucus is expelled. Mucus also may exist smeared on the tail, thighs, flanks, or perineal region.
Cord of clear mucus being discharged.
Swelling and Reddening of the Vulva
During estrus the vulva swells and the interior becomes moist and red. More often than not these symptoms appear before heat and remain for a curt menstruation afterwards heat. Thus they are non precise indicators of estrus. During midcycle the lips of the vulva are pale and more difficult to separate.
Bellowing, Restlessness, and Abaft
Cows in heat are more restless and alert to their surround. When allowed to interact with other cattle, cows coming into rut "proestrus" and cows in heat persistently trail behind to effort to mountain other cows. Research shows that cows in heat spend less time resting than nonestrous herdmates. Prior to and during heat, they remain standing and alert while their herdmates are lying downwards and resting. This is more noticeable for stanchioned cows. Cattle may blare more oftentimes during estrus. Although these are not definitive signs of estrus, cows exhibiting such beliefs should be watched closely for standing behavior.
Rubbed Tailhead Hair and Dirty Flanks
As a consequence of being ridden, the pilus on the tailhead and rump is fluffed-upwards, rubbed, or matted, and the peel may be exposed. The legs and flanks may be smeared with mud or manure.
Chin Resting and Dorsum Rubbing
Prior to mounting, cows often rest or rub their mentum on the rump or back of the cow to be mounted. This awarding of pressure may be considered a test for receptivity to being mounted. Both cows should be observed closely for mounting and standing behavior.
Chin resting and trailing activity.
Sniffing Genitalia
Sniffing the genitalia and licking the vulva of other cows occur much more than frequently with cows in proestrus and oestrus.
Head Raising and Lip Curling
Generally this action follows sniffing of the genitalia and occurs more than oft if the cow existence investigated is in heat and urinates.
Decreased Feed Intake and Milk Yield
Estrous cows spend less time feeding. Some studies likewise have reported decreased milk yield during estrus, and a Canadian report reported a slight increase in milk yield toward the end of heat. But since many factors other than estrus tin affect milk yield on a specific twenty-four hour period, this is not a reliable indicator of estrus.
Metestrous Haemorrhage
Some cows and most heifers accept a bloody mucus discharge one to iii days subsequently estrus, only onset of this symptom, called metestrous bleeding, is quite variable. High estrogen levels during rut cause claret to leak from vessels near the surface of the uterus. This discharge indicates that the cow was in rut and does not hateful that she failed to conceive. Yet, such animals should be watched closely for a return to heat in 18 or 19 days.
Factors Affecting Estrous Behavior
Arrangement where cattle are crowded.
Type of Housing
Any housing arrangement that allows cattle to interact throughout the mean solar day provides more than opportunity for mounting and standing beliefs to exist expressed. Cattle housed in necktie-stall or stanchion barns must be turned out in order for this beliefs to be expressed. If cattle are not allowed to interact, the herd manager must use less reliable secondary signs to determine which cows are in heat. Caution: Information technology would be wrong to assume that more heats are observed in loose-housing or free-stall barns than in tie-stall or stanchion barns. Although there is a greater opportunity to observe heat when cows collaborate frequently in free-stall barns, taking time to detect estrous behavior is still necessary.
Footing Surface
To what extent does a slippery ground surface affect expression of oestrus? Research conducted in North Carolina compared estrous activity of high-producing Holstein cows that were watched for heat for ane hour every eight hours, thirty minutes on dirt and 30 minutes on grooved physical. Table 1 shows total mounts and stands during oestrus and average number of mounts and stands during a 30-minute heat check period. Duration of heat was longer for cows observed on clay. Mounting and continuing behavior were nearly doubled when cows were checked for heat on clay as compared to physical.
| Activity | Dirt | Concrete |
|---|---|---|
| Source: J. Britt et al. (1986), Journal of Dairy Science 69: 2195. | ||
| Duration of oestrus (hours) | 13.eight | 9.iv |
| Total during rut | ||
| Mounts | 7.0 | three.ii |
| Stands | six.iii | 2.9 |
| Average during 30-minute heat check | ||
| Mounts | 3.7 | 2.5 |
| Stands | 3.8 | 2.seven |
A second study also confirmed that mounting activity occurs more frequently when cows are on dirt rather than physical. When v estrous cows were individually presented with an opportunity to spend time on dirt or on physical in the presence of a tied moo-cow which was either an estrous cow or a cow not in rut, the test moo-cow spent an average 70 per centum of the fourth dimension on clay. The test estrous cow mounted more frequently when a tied estrous moo-cow was on dirt rather than on concrete.
Finally, in a Purdue Academy study in which heifers were housed in a free-stall barn with access to a bedded pack and observed continuously for estrous beliefs over a 96-hr period, 70 pct of the mounting activeness occurred in the bedded pack area. Less activity was observed in the dry lot, in the gratuitous-stall area, and near the feed bunk (Table 2).
| Location | Mounts and standing behavior | |
|---|---|---|
| Number | % of full | |
| Source: J. Pennington et al. (1985), Agri Exercise, Vol. 6, No. 9. | ||
| Bedded pack | 1098 | 70 |
| Dry lot | 204 | 13 |
| Feed bunker of manger expanse | 108 | 7 |
| Complimentary-stall surface area | 94 | 6 |
| Free-stalls | 55 | four |
Icy or slick concrete is always a problem for complimentary-stall herds. Concrete should exist grooved or scabbled to provide traction. Moving cattle to a dirt lot or from one expanse to another non only provides a meliorate surface but too provides added stimulation from the movement alone.
Anxiety and Leg Bug
Cows with sore feet or legs or poor structural conformation showroom less mounting action, or they stand to be mounted when non in heat considering it is too painful to avoid being mounted. I British written report involving 770 cows with nearly 1500 lactations showed that lameness caused by specific lesions on the hoof was associated with a 7-day increase in days to first service and 11 more days open compared to herdmates without lameness. These differences were greater for cows with sole lesions that developed betwixt 36 and 70 days postpartum, the fourth dimension when cows should first exist detected in heat. For those cows the interval to offset service and days open increased 17 and thirty days, respectively.
Cow Density
Data are not bachelor for determining optimal number of open cows per unit area or total number of cows per pen to achieve maximum expression of estrous behavior. However, common sense would propose that if cattle are forced into a crowded area, such as a belongings pen associated with a milking parlor, that mounting action would be suppressed or cows would be forced to stand up to be mounted even when they are not in heat. Too oftentimes the only time cows are observed for rut is when they are in holding pens prior to milking. In overcrowded complimentary-stall barns, cows may stand up to be mounted in a stall or alley just because they cannot escape a mounting moo-cow. Crowded conditions likewise may increase the incidence of false-positive heats adamant by rump-mounted heat detection devices or markings.
Temperature
Research conducted in Virginia showed that every bit maximum daily temperatures increased to about 75°F, mounting activity also increased. But at temperatures above 85°F, beyond the comfort range for cattle, mounting was less frequent. Research done at Purdue University suggests that cows in cold weather have more than mounting activity than cows exposed to hot weather condition; however, during hot weather estrous cows tend to exhibit more secondary signs, such every bit rubbing, licking, and chin resting.
Variation During the Day
Do cows prefer to mountain other cows at a certain fourth dimension of 24-hour interval? Herd managers often remark that most mounting occurs in early forenoon or during the later on evening hours. In a study conducted in Canada, video cameras monitored estrous activity in a free-stall area 24 hours a day. This study showed that about 70 percent of the mounting occurred between seven p.k. and vii a.m. (Figure two). This observation suggests that cows are virtually likely to showroom mounting activity when they are non distracted by farm activities such as feeding, milking, and barn cleaning. The data may further indicate that cattle prefer to mountain during the cooler times of solar day.
Effigy two. Effect of time of day on mounting activity for estrous cows. Adapted from Hurnik et al. (1975)
Herdmate Condition (Stage of Estrous Cycle)
To make up one's mind the crusade of silent heats or poor expression of heat, consider the overall reproductive status of the herd and compare the ratio of open to pregnant animals in each group of cows and heifers. Pregnant cows are the least likely group of herdmates to mountain a cow in heat. Herd managers must rely on the other open cycling herdmates to detect oestrus. What nearly the other nonpregnant herdmates? Exercise herdmates vary in their ability to detect and mount cows in rut? Does the 24-hour interval of the herdmate's estrous cycle influence her interest in the estrous cow?
When Penn Country researchers conducted a very controlled report, estrous cows encountered each of nineteen cycling herdmates in an isolated barn one-to-one for x minutes. The total number of mounts past each herdmate was determined on day x, twenty-four hours 15, solar day of heat, and 24-hour interval five of the next cycle. Herdmates varied in mounting action, every bit did estrous cows in alluring mounts. More of import, for the herdmates as a group, the number of mounts differed substantially with the solar day of the bike. Herdmates in midcycle (day 10 and day 15) and on twenty-four hour period 5 averaged one mountain or less during the ten-infinitesimal observation period. Some herdmates did non even mountain the estrous cow on those days. Withal, when the herdmate herself was in oestrus, the number of mounts averaged 2.5 during the 10-minute period. Thus, taken as a group, cows are poor heat detectors in the middle of their bicycle. Since this represents 50 to lx percent of the estrous cycle and reduces the number of constructive rut-detecting herdmates past a similar pct, managers must rely on cows in or near heat to detect other estrous cows.
In some herd situations, a few open cycling cows may contribute to the problem of silent or missed heats. In modest herds, almost of the herd may be pregnant at certain times, and the stage of the cycle of the few nonpregnant cows may be such that they are not effective heat detectors. Equally more animals become significant, the number of potential heat-detecting animals is reduced. The situation is similar for herds that freshen on a seasonal basis. After an intensive breeding period, when a high percent of the herd is pregnant, it becomes increasingly hard to identify the few open cycling cows in oestrus. There simply may not be enough herdmates in the proper phase of the wheel to interact with an estrous cow. A 3rd state of affairs may occur frequently in free-stall herds where cows are grouped according to production. Mostly, the lower production group contains pregnant cows, merely because of depression production, some nonpregnant cycling cows may exist included in this group. Information technology becomes very difficult to observe the cows in heat because their herdmates are significant.
Number of Herdmates in Proestrus or Estrus
Frequency of mounting is considerably higher when more than one moo-cow is in heat or budgeted heat (proestrus) at the same time. Canadian scientists institute that the number of mounts increased significantly when 2 or more than cows were in rut simultaneously (Table 3).
| Number of cows | Average mounts per cow in heat |
|---|---|
| Source: J. Hurnick et al.(1975), Applied Animal Ethology 2:55. | |
| ane | 11.2 |
| 2 | 36.vi |
| three | 52.6 |
| 4 or more | 49.8 |
Nutritional Factors
Mounting activity and other sexual behavior have been shown to decrease in cows that lost more weight since calving than herdmates with minimal weight loss. On the other hand, there are certain cows within the herd or entire herds in which the majority of the cows are truly anestrus (noncycling). Possible causes of anestrus include poor body condition, anemia, uterine infection, cystic ovaries, and parasitism.
Lactation Number, Days Postpartum, and Milk Product
With the possible exception of heifers, lactation number does non seem to affect estrous behavior. Variable results take been obtained from research comparison estrous behavior with level of milk production or number of days postpartum. These factors accept much less influence on the expression of estrus than other factors described above.
Estrous Detection Plan
Heifers on dirt lot with practiced footing.
- Use your time efficiently, observing for heat when cattle are likely to mount.
-
Allow cows to interact, especially during the evening and early on morn hours, when most of the mounting activity occurs. Even though loose housing systems provide more time for cow interaction, be sure to discover the cattle frequently. Move pastured cattle to an surface area where they easily can be observed. In conventional housing systems, turn cows out twice daily for 20 to 30 minutes. Be sure to plough cows out when time can be spent observing them. Avert scheduling observation periods at feeding time or during the warmest hours in summer.
An aggressive rut detection program tin can be constructive. A Pennsylvania written report involving approximately 200 repeat breeding heifers (iii or more services) compared the average and distribution of cycle length based on farm records before the heifers arrived at the research station with these estrous cycle characteristics after arrival. The major difference in direction was that the heifers were turned out for heat detection at 8:00 a.chiliad., 4:00 p.grand., and midnight. The average elapsing of cycle length and the frequency of long cycles were reduced. The onset of heat occurred equally for the three heat detection periods. Tabular array 4 shows that the more frequent the observation, the more than heats are detected.
- Slippery and muddy conditions severely inhibit mounting activity. Provide an area with a skillful basis surface where cattle are free to interact and where few obstacles hinder motion. Moving cattle to a separate area for heat detection may stimulate estrous behavior.
- When cows have sore anxiety and legs, heat detection is more difficult. Minimize this problem by trimming hoofs periodically, and treat infected anxiety as soon as a problem is apparent.
Cows on grooved concrete. - When several people are working with the herd, assign one person to be responsible for heat detection, and allow fourth dimension for employees to do the chore properly. Train employees to recognize signs of heat and promptly report this information to the responsible person. Consider having a financial incentive programme to increase oestrus detection efficiency.
- Studies have shown that upward to 15 percent of the cattle presented for insemination are actually non in estrus. Poor moo-cow identification tin can be ane crusade of this problem. Legible neck chain numbers, big ear tags, and freeze brands can assist in accurate identification and can reduce mistakes.
- Record all heats, whether the animal is to exist inseminated or not. Heat detection volition better if future heats can be predictable. Employ a pocket notebook to record heats and other information. Transfer information to a rut expectancy chart and to the permanent individual cow record. This permits monitoring of abnormally long cycles and long intervals from freshening to first service.
- Consider using estrus detection aids to help increase the number of heats detected. Detection devices and detector animals should supplement routine visual ascertainment.
- In larger herds the utilise of a testosterone-treated heifer will stimulate more mounting and probably will be cost effective.
- Using prostaglandin to induce estrus in ane or two cows will increase the overall estrous behavior in the herd.
- Estrous synchronization programs for the lactating herd, or programmed breeding, will synchronize estrus for several days. Also, more heats will be predictable and thus more heats are likely to be observed.
- Isolate the moo-cow thought to be in heat with a sexually active cow or heat-detector creature. Estrus may not be detected in some cows in a big group situation, but when isolated with an agile moo-cow or heifer, a cow possibly in heat may exhibit standing behavior.
- Watch for sexually agile groups of cattle. Cows in proestrus or estrus tend to congregate and stay together.
- Adjust the feeding programme so that cows calve in proper torso condition and weight loss is minimized during lactation.
| Boilerplate interval between heats | % short cycles <17 days | % normal 18-24 days | % long cycles >24 days | |
|---|---|---|---|---|
| Source: T. Tanabe and J. Almquist (1960), Penn State Research Message 672. ¹ Heifers observed at 8:00 a.m., 4:00 p.thou., and midnight. | ||||
| Earlier | 48.vi | 6.iii | 41.9 | 51.eight |
| During¹ | twenty.6 | 9.ix | 81.i | nine.0 |
Group of sexually active cows.
Timing of Insemination
Cow with big ear tag for like shooting fish in a barrel identification.
Ovulation occurs 25 to 32 hours after the onset of standing heat. Standing behavior is the only reliable symptom producers have to determine time of ovulation.
Sperm take to be in the female reproductive tract for approximately six hours before they are capable of fertilizing the egg. This process is termed capacitation. Although live sperm take been found in the female tract up to 48 hours afterwards insemination, sperm viability normally is estimated to exist 18 to 24 hours. Improper semen handling or poor insemination technique can dramatically reduce the number of sperm cells bachelor for fertilization and thus tin can lower the conception rate.
The egg travels very rapidly from the ovulation site to the fertilization site in the oviduct. The fertile life of the egg is shorter than that of the sperm. Ovulated eggs remain fertilizable longer (10-20 hours) than they remain capable of being fertilized and developing into normal embryos (8-x hours). The likelihood of embryonic decease increases as the time beyond this interval increases. Thus viable sperm should exist at the site of fertilization awaiting the arrival of the freshly ovulated egg. Breeding either also early or likewise late allows an aged sperm or an aged egg to interact at the site of fertilization and volition result in poor conception. Events and time intervals associated with standing heat and insemination are summarized in Figure 3.
Effigy 3. Boilerplate time relationships amidst reproductive events.
Cattle should be inseminated during the last half of standing rut. The a.chiliad.-p.m. rule was developed as a guide. Cows get-go seen in standing heat in the morning time (a.m.) would be inseminated in the afternoon (p.m.) and those observed continuing in the evening would be bred the adjacent morning. This system was based on inquiry in which cows were observed frequently (4 to 12 times per twenty-four hour period), immune to collaborate, and exhibited mounting/continuing behavior. Furthermore, insemination was based on continuing estrus, not secondary signs. Under such conditions, heat detection was very skillful. But herd managers may non be in a position to accurately predict the latter half of the heat menses. Generally it is a challenge but to notice standing behavior. Knowing when to inseminate is another management challenge.
More recent studies conducted past artificial insemination organizations and universities reexamined timing of insemination. In a Virginia study with twice daily rut checks, cows were inseminated either at the terminate of the heat cheque period in which they were first observed in heat or at the end of the next oestrus cheque period. Using a routine viii:00 a.m. and viii:00 p.m. heat detection organisation, waiting 12 hours to inseminate resulted in a slight numerical advantage in pregnancy rate over inseminating immediately afterward heat was first observed (55% vs. 51%). Withal, this was not a meaning difference. Thirty percent of the cows stood to be mounted at the 12-hr oestrus cheque subsequently they were offset observed in standing heat. These cows had higher pregnancy rates than their herdmates, whether they were inseminated immediately after existence showtime observed in heat or 12 hours subsequently.
Results from a field study in New York showed that near optimal fertility was obtained with a single morning insemination of all cows in oestrus from the previous evening, including those in estrus that morning. This result suggests there may be a benefit to earlier breeding under farm conditions.
Applying this information to a herd situation suggests the following guidelines:
- Best fertility is obtained when cattle are inseminated during the last half of standing heat.
- If a management schedule permits routine heat checks and if it can decide when a heat began and thus predict the latter portion of the estrus, the a.m.-p.chiliad. system should be used.
- If the conception rate is unsatisfactory or estrus detection is non routine, cows should be inseminated soon after they are first detected in standing heat. Waiting 10 or 12 hours probably results in most of the cows being bred too late.
- Think, factors other than timing of insemination tin affect the conception rate.
Milk Progesterone Analysis every bit a Tool for Heat Detection
The concentration of progesterone in claret is correlated closely with levels found in milk. The relative relationship betwixt milk and blood concentrations is the same. Progesterone is low during proestrus and during oestrus. It begins to rise slowly after ovulation as the CL develops.
Verifying suspicious heats
If the herdsperson is suspicious that a cow is in oestrus, milk progesterone concentration can be used to verify that the cow is in or near heat. Such testing may be useful in the following situations:
- The cow was observed in estrus, but was previously diagnosed pregnant.
- Continuing heat was observed, but the interestrous interval was abnormally long.
- The cow was detected in oestrus based solely on secondary signs.
Evaluating heat detection accuracy
Numerous studies using milk progesterone assay have shown that v to 15 percent of cows are inseminated when they are not in or near rut. Milk progesterone testing can be a reliable method of evaluating the accuracy of heat detection on an individual subcontract. To make the evaluation worthwhile, 15 to twenty cows should be sampled on the twenty-four hour period of insemination. Milk samples should exist obtained at the milking immediately later on insemination. When compared with a standard progesterone sample, the milk obtained on the day of insemination should have low progesterone.
If more than 5 percent of the samples have high progesterone, the heat detection mistake rate is also high. A few samples may have intermediate concentrations of progesterone, suggesting that it may be declining, but has not withal reached a minimal level, or that information technology is rising and low concentrations already have occurred. No definitive interpretation can be fabricated from such results.
Dairy producers and veterinarians must realize that progesterone is low for about six days around the time of oestrus. Thus low progesterone indicates the cow is either in or near rut, merely progesterone levels cannot be used to precisely time the insemination. Errors in estrus detection should be considered the main cause of depression formulation in problem herds. Milk progesterone analysis is a tool to help determine whether a heat detection problem exists.
Evaluation of Heat Detection Efficiency
Complete and accurate records including all heats, services, and veterinary exam findings are needed to calculate heat detection efficiency. Some DHIA processing centers and herd management computer programs provide a heat detection index.
There is a difference between the accuracy and the efficiency of oestrus detection. Inaccurate heat detection occurs when cattle are inseminated merely are not in true estrus. Inefficient heat detection simply refers to besides many unobserved or missed heats. Many reproductive problem herds experience both inaccurate and inefficient heat detection.
Characteristics of Herds with Heat Detection Errors
- Estrous intervals between 3 and 17 days exceed x per centum.
- Estrous intervals betwixt 25 and 35 days exceed 10 to 15 percent.
- Cows inseminated one day and again within three days exceed 5 percent.
- Several cows are checked pregnant to a service before than the last one recorded.
- Several cows calve usually three to six weeks earlier the expected calving date.
Characteristics of herds with missed heats
- Very few heats are observed and recorded before showtime service.
- Average days to first service exceed fourscore days when the voluntary waiting period to first service is sixty days.
- Average interval between breedings exceeds 30 days.
- Estrous intervals between 38 and 45 and 55 and 65 days exceed fifteen percent.
Estrous detection goals
- 85 pct of the cattle are detected in estrus by threescore days postpartum.
- Days to first service are 75.
- sixty percent of the estrous intervals are between 18 and 24 days.
- Ratio of the number of 18-24 to 36-48 day estrous intervals exceeds 4:ane.
- At to the lowest degree seventy percent of the heats are detected.
Heat detection efficiency equations
Several methods are used to express efficiency of estrous detection. These indexes are used to express the percentage of cows detected in rut relative to number of cows really in estrus. They provide an estimate of the intensity of estrous detection but do not measure accuracy. The frequency of prostaglandin utilise to induce estrus and shorten the interestrous interval should exist considered when evaluating these indexes.
Percentage of Possible Heats Detected
The full number of services and reported heats for a grouping of cows during a specified period of time is divided by the full days in the period divided past 21. This is most useful in a beef cattle breeding plan.
Instance: If xx heats were observed in a group of forty beef cows over a 24-twenty-four hour period period, the estimated per centum of heats detected would be calculated as follows:
Percentage of Breedable Heats Detected
A breedable estrus is defined every bit any heat occurring beyond the voluntary waiting period for a specific herd. The voluntary waiting menstruation (VWP) is the interval of time from calving until the managing director is willing to rebreed the cattle. The number of breedable heats tin can be estimated by this formula:
If the VWP were 50, the start breedable heat beyond 50 days would be detected on the average at day 60 postpartum (10 days is half an estrous cycle). The per centum of breedable heats detected tin can then exist estimated by the formula:
If this index is to be authentic, all observed heats must exist recorded. The pct of breedable heats detected is not afflicted past conception rate or the conclusion to delay breeding.
Estrus Detection Alphabetize (Efficiency)
Several formulas have been developed to determine the efficiency of estrus detection.
- Interestrous interval method: normal cycle length is divided by average interval between consecutive services or heats for all eligible cows.
-
Instance: 21 ÷ 32 ten 100% = 65.6%
- Convenance interval (BI) methods: These are good indicators of heat detection efficiency after get-go service. DO refers to days open. (Table 5 shows percentage of heats detected.)
- 1. Meaning Cows
- a. Convenance interval method using days to commencement service:
- b. Convenance interval method using voluntary waiting menstruum (VWP):
- a. Convenance interval method using days to commencement service:
- ii. All cows serviced (services per cow) Services per cow includes average number of services for pregnant cows, cows examined for pregnancy and found open, and cows serviced with at least 45 days elapsed since breeding, but not nevertheless examined for pregnancy.
- a. Convenance interval method using days to outset service:
- b. Breeding interval method using VWP:
Example: days open = 126, days to first service = 85, and services per cow = 2.0
% heats detected (Table 5) = 51%
- a. Convenance interval method using days to outset service:
- 1. Meaning Cows
| Breeding interval | % of heats detected |
|---|---|
| D. Grusenmeyer et al. (1983), Western Regional Extension Publication 67. | |
| 23 | 91 |
| 26 | 81 |
| 30 | 70 |
| 35 | 60 |
| 41 | 51 |
| 50 | 42 |
| 60 | 35 |
If complete data including days to first service, days open, and conception rate are available, Table half-dozen on the adjacent page can be used to estimate estrus detection efficiency.
| Source: G. McGilliard et al. (1979), Dairy Guideline 54: Evaluating Heat Detection, Virginia Polytechnic Institute and State University. Note: In developing these tables, all cows were assumed significant past 200 days. | ||||||||
| 60 days to first service (average betwixt fifty and 70 days) Conception rate (%) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Always days open | 35 | 40 | 45 | fifty | 55 | sixty | 65 | seventy |
| 150 | 33 | 28 | ||||||
| 140 | 42 | 37 | 33 | 29 | ||||
| 130 | 52 | 45 | forty | 34 | 33 | 30 | ||
| 120 | 63 | 55 | 51 | 45 | xl | 37 | 35 | 32 |
| 110 | 77 | 68 | 60 | 54 | 49 | 45 | 42 | 39 |
| 100 | 93 | 83 | 73 | 66 | 60 | 55 | 51 | 47 |
| ninety | ninety | 82 | 74 | 68 | 63 | 58 | ||
| fourscore | 93 | 85 | 80 | 74 | ||||
| seventy days to first service (boilerplate betwixt 60 and fourscore days) Conception rate(%) | ||||||||
| Always days open | 35 | 40 | 45 | 50 | 55 | lx | 65 | 70 |
| 160 | 29 | |||||||
| 150 | 39 | 33 | thirty | |||||
| 140 | 49 | 43 | 38 | 35 | 32 | 28 | ||
| 130 | 62 | 53 | 48 | 43 | 39 | 34 | 33 | 31 |
| 120 | 75 | 66 | 58 | 53 | 48 | 44 | forty | 38 |
| 110 | 93 | 82 | 73 | 65 | 60 | 55 | 50 | 47 |
| 100 | 90 | 81 | 73 | 68 | 63 | 58 | ||
| ninety | 93 | 86 | 79 | 73 | ||||
| fourscore days to first service (average between lxx and 90 days) Conception rate(%) | ||||||||
| Always days open | 35 | 40 | 45 | 50 | 55 | lx | 65 | seventy |
| 160 | 34 | thirty | 27 | |||||
| 150 | 45 | 40 | 35 | 32 | 28 | 26 | ||
| 140 | 58 | 51 | 45 | 41 | 37 | 34 | 32 | 29 |
| 130 | 73 | 64 | 57 | 52 | 47 | 43 | 40 | 37 |
| 120 | 91 | 80 | 72 | 64 | 58 | 54 | 49 | 46 |
| 110 | 89 | 80 | 73 | 67 | 62 | 58 | ||
| 100 | 93 | 85 | 79 | 73 | ||||
| 90 days to first service (average between 80 and 100 days) Formulation rate(%) | ||||||||
| E'er days open up | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
| 170 | 29 | |||||||
| 160 | 41 | 36 | 31 | 28 | ||||
| 150 | 54 | 48 | 42 | 38 | 35 | 32 | 29 | 27 |
| 140 | lxx | 62 | 54 | 49 | 45 | 41 | 38 | 35 |
| 130 | 89 | 78 | seventy | 63 | 57 | 52 | 48 | 45 |
| 120 | 88 | 80 | 72 | 66 | 62 | 57 | ||
| 110 | 93 | 85 | 78 | 73 | ||||
Estrous Detection Aids
Records
No matter which record system is used, the information should exist posted and available to all farm employees. The more than people anticipating and watching for the oestrus, the more probable oestrus detection efficiency will be maximized. All heats, including those observed in the early postpartum catamenia, must be recorded. Finally, tape systems should be used on a daily basis.
Heat Expectancy Nautical chart
Special calendars are bachelor from artificial insemination organizations. Most charts are organized on a 21-day cycle and then that future heats tin exist anticipated. Some herd managers mark day 19 post-obit insemination and then that the expected heat can exist predictable several days in advance.
Breeding Wheel or Herdex Record Arrangement
These wall-mounted reproductive tape systems utilise color-coded pins or markings to bespeak reproductive events for each moo-cow. By either turning a transparent plastic dial or sliding the plastic cover on a daily basis, future heats and reproductive events can be anticipated.
Computer Generated Action Lists
Some dairy management computer programs can generate listings of cows that require special attention or action on a specific mean solar day. Action lists betoken cows to watch closely for return heats or cows that take non yet been observed in heat.
Prostaglandins
If more than one animate being is in proestrus or estrus simultaneously, mounting behavior increases and continuing behavior is more likely to exist observed. Depending on herd size, it may be worthwhile to inject one or more cows with prostaglandin at diverse intervals during the week to induce more estrous beliefs in the herd.
Mount detection aids
Studies have confirmed that using conventional mount detectors such as Kamar devices and tailhead markings without visual observation for estrous results in lower pregnancy rates. Withal, normal pregnancy rates and improved heat detection efficiency are obtained when mount detector systems are used to supplement visual observation.
Kamar Force per unit area-Sensitive Mount Detectors
These devices are glued on the topline of the rump forward toward the hooks according to the size of the cow. Sustained pressure level for several seconds by the sternum of the mounting moo-cow will expel scarlet fluid from a modest storage chamber into a larger visible plastic bedroom. The detectors should exist placed further forward on small cows to avoid false activation when large cows attempt to mount them.
The devices can be used for various groups of cattle. To help detect early postpartum heats, they tin be applied to cows at 30 days postpartum. Some managers employ them to find heat for cows not observed in heat by the voluntary waiting period (40, fifty, or 60 days). Several days after a heat or insemination, the devices are put on cattle in an attempt to detect evidence of mounting activity during the side by side return rut. They can be helpful in detecting estrus after an estrous synchronization programme has been established.
Follow these guidelines when using mount detectors:
- Store detectors and adhesive in a cool, dry environment.
- Apply properly co-ordinate to the size of the animal; don't use an excessive corporeality of agglutinative.
- Write the cow'southward ID on the detector. If information technology comes off, the moo-cow can be identified and observed carefully for other signs of heat.
- Exercise not clip hair or apply the adhesive to moisture hair.
- Leave partially activated, or "triggered," detectors on the cows for several additional days. These cows may be in proestrus.
- Remove obstacles such equally low branches, cattle dorsum rubbers, and oilers from the pasture, exercise lot, or free-stall befouled. Such items tin be rubbed and tin actuate the mount detector. This would consequence in a false positive.
- Be aware that the orientation of certain partitions and stall dividers tin inadvertently activate these devices.
Falsely activated detectors may also be an indication that the devices were applied too far dorsum on small animals. Fake positives are more frequent when cattle are confined in crowded pens or when cattle infested with external parasites rub or scratch their backs. Partial activation may event when an animal is trapped in a mounting situation but is not in estrus. Conscientious estimation is essential to efficiently use mount detectors. Tabular array seven compares the pregnancy rates among groups of beefiness cattle with fully activated, partially activated, or missing detection devices at the time of engagement insemination 80 hours after prostaglandin injection. Cows missing devices or with fully activated detectors had significantly higher pregnancy rates compared to cows with partially activated detectors.
| Detector status | % pregnant |
|---|---|
| Source: C. Marshall et al. (1978), Proceedings of the Extension-Manufacture Workshop on Beef Cattle Reproductive Management. | |
| Fully activated | 67 |
| Partially activated | 23 |
| Missing | 51 |
Tailhead Markings
Marking the tailhead with chalk, paint, or crayon and observing for prove of rubbed off or smeared markings is less expensive than Kamar detectors and has gained popularity in larger herds. Markings 10 to 12 inches long and 2 to three inches wide are made across the tailhead with a livestock marking crayon or oestrus detector pigment. Tailhead paint is less convenient to utilise than crayon but lasts longer (upward to iii weeks). This system works about effectively in loose-housing arrangements where cattle tin can be restrained in self-locking headgates to exist marked or observed for bear witness of smeared or rubbed-off markings, which indicate the animal was mounted. Markings can as well be touched upwards at this time.
Imitation positives can occur for rea- sons similar to those with Kamar detectors. Cattle may demand to be remarked every three or four days. Ane hidden reward of this arrangement is that when marking or examining the rump region of the cow, the manager may observe mucus discharge, smeared mucus on the tail, swollen and reddened vulva, aberrant vaginal belch, or metestrous bleeding. In larger herds many of these symptoms go unnoticed. Tailhead mark is cheap and large groups of cattle can exist marked in a brusque period of time.
Electronic Mount Detectors
Mount detectors are beingness adult which detect and record legitimate mounts. Each detector is coded with the moo-cow'southward identification number, and the information is transmitted to a computer to be stored. At regular intervals during the day, the herd director tin can access the information to determine which cows were mounted at a particular time. Various prototypes are currently being tested.
Videotape
This system has been used extensively in research to continuously monitor estrous behavior. The cattle must exist clearly identifiable from a distance and must be allowed to interact in a loose-housing arrangement. The video photographic camera(south) should monitor a large proportion of the housing area. Several cameras may have to be strategically positioned, and the video equipment should be protected from moisture. This system volition exist effective only if the videotapes are reviewed daily, especially afterward the herd has been monitored in the evening. The disadvantages are the initial investment for buy and installation of the equipment and the time required to review the tapes. If used properly, however, videotaping is a very efficient and accurate estrous detection organisation.
Heat detector animals
Oestrus detector animals can reduce the days to first service and can ameliorate estrous detection in the herd if they are used properly and supplement visual observation. Notwithstanding, managers must realize that on an private basis, surgically contradistinct bulls or hormonally treated females vary in their sexual aggressiveness.
In general, such animals take been shown to exist effective in detecting heat. The more animals sexually active at one time, the more mounting will occur with each moo-cow in heat. If allowed to interact with the herd throughout the day, detector animals provide a continuous monitoring of estrous behavior. If stanchioned cows are turned out daily for heat detection or cows in loose-housing are checked regularly for estrus just heat detection does not seem to be constructive, then use of a oestrus detector animal should be considered.
Male person Issue
Enquiry has shown that in a beef herd the introduction of a bull shortens the interval to first estrus during the early postpartum catamenia. The physiological machinery for this outcome is unknown.
Vasectomized or Surgically Altered Bull
A vasectomized bull or a bull with a surgically altered penis tin be an effective heat detector. These animals can be almost effective if they are equipped with a mentum-brawl or ballpoint marking harness which marks the loin and rump of cows that were mounted with a bright-colored marker solution. Surgically altering the penis of a balderdash to prevent intromission may be more costly than vasectomy, but this method is preferred since vasectomized bulls can copulate with cows and possibly spread disease.
With either method of preparing a bull, the beast will seek out cows in proestrus and estrus and possibly stimulate the overall estrous activity in the herd. These animals tin be used with beef cattle to stimulate early on estrous activeness (male upshot) and and so exist removed from the herd to allow natural service to embark or they tin can remain with the herd for enhanced heat detection during an artificial insemination programme. The major disadvantage is the danger of handling a balderdash and allowing him to interact with farm employees. There also is the veterinary cost of performing the vasectomy or surgical alteration and general veterinary costs of maintaining the bull.
Testosterone-Treated Female
Testosterone, a male hormone, causes increased sexual aggressiveness when injected or implanted into cows or heifers. Potential nonlactating cull cows or heifers, even freemartin heifers, are candidates for masculinization. Nearly people who accept used this organisation prefer cows that accept completed a lactation. Nevertheless, there are several reports of success with freemartin or virgin heifers. A typical treatment regime consists of administering 200 mg of testosterone propionate intramuscularly every other day for three weeks. Some veterinarians accept used larger doses (500 to 600 mg) once weekly or a single injection of two grams of testosterone enanthate in corn oil given in three or 4 locations. When mounting activity is increased following these initial injections, the moo-cow is given a maintenance injection of about 500 mg testosterone propionate, enanthate, or repository testosterone every ten to 14 days.
The interval between maintenance (booster) injections should be adjusted on the basis of sexual activity of the detector animal. Some veterinarians adopt to utilize several Synovex-H implants for a maintenance program. These implants contain testosterone and estradiol.
The results of a trial comparing heat detection methods of routine visual observation past a herdsperson with use of a surgically altered bull or a testosterone-treated moo-cow are presented in Table 8. Although not a meaning number, more heats were detected in the group of cattle with the testosterone-treated moo-cow. Formulation rates were similar for all groups.
| Method | Number | Pct detected | Formulation rate |
|---|---|---|---|
| Source: T. Kiser et al. (1976), Periodical of Animal Science 44:1030. | |||
| Herdsperson | 31 | 67 | 62 |
| Surgically altered balderdash | 30 | 70 | 62 |
| Testoterone-treated moo-cow | 29 | 84 | 67 |
The following should be considered in using testosterone treatment:
- Testosterone treatment is an extra-label utilize of this hormone. The FDA has non specifically approved using testosterone for this purpose. Guidelines must be followed on the withdrawal period before treated animals can be marketed.
- While a big pct of the females reply to the testosterone, some do non.
- It may be helpful to remove the estrous cow from the grouping so that the detector cow can search for other estrous cows.
- Select a good for you cull cow or heifer that has sound feet and legs and is large enough to mount and mark other cows. Heifers must be sexually mature. Do non utilise a lactating or significant animal.
- Treated females can be equipped with a chin-brawl mark harness or the herd can be marked with crayon, chalk, or heat detection paint or tin be fitted with mount detectors and then that mounted cows can be identified.
- This rut detection help will exist effective merely when used in conjunction with routine visual estrus detection.
- Maintaining a ratio of one treated female to every 30 open cows is necessary to maximize detection efficiency. In large herds, it may be beneficial to have more than one detector animal per herd. Such animals could be rotated on alternate weeks.
- This system can be effective in both loose-housing and stanchion barn housing, provided cows are turned out and allowed to interact.
- Avert assuasive the treated animal to get overconditioned.
- Testosterone-treated females in general are not dangerously aggressive.
- Consult your veterinarian concerning the method of testosterone treatment.
Vaginal electric resistance
In early research washed in Europe, the electrical resistance (ER) of vaginal fluids decreased during proestrus and through the estrous period. Numerous studies have validated this concept. Several probes that mensurate the ER of vaginal fluids are now commercially available.
Vaginal electrical resistance probe.
Although the concept is physiologically sound, the challenge is to adapt this engineering to a management state of affairs. Resistance measurements vary amongst cows; all the same, monitoring the relative changes inside cows during the estrous cycle tin provide the herdsperson with additional information and tin serve equally a estrus detection assistance if cattle are probed frequently. Once the ER readings brainstorm to decline, the cow should be probed every 12 hours until the lowest reading is obtained. Theoretically, this reading coincides with the fourth dimension of continuing heat.
This tool is labor intensive since cattle must exist probed frequently to detect significant changes in ER. The probe likewise is expensive. It must be washed in disinfectant, thoroughly rinsed, and dried earlier information technology is used in some other cow. Without proper sanitation, the device could spread disease among cows.
Miniature electronic devices are being developed which are implanted into the vaginal tissue. They continuously monitor ER and transfer the information to a romote receiver and computer.
Activity monitors
It is well documented that cattle are more active during estrus and thus spend more time walking and continuing than resting. Researchers at the USDA facility in Beltsville used pedometers to monitor cow activity between milkings. The study showed that activity increased approximately 400 per centum during estrus for cows housed in a gratis-stall barn, and 275 percentage for cows in comfort stalls. During this study, 76 percent of the estrous periods were detected by visual observation and 96 percent were detected past changes in pedometer readings.
Since those initial studies, various pedometers have been developed and tested. Early prototypes were often inaccurate because of a high rate of faux positive signals. Accuracy in identifying true estrous periods has improved in the newer models, which compare activity during a specified interval with activity during the same menstruum on the previous solar day or the previous three days.
If pedometers are used properly and the equipment remains functional, this method tin can exist effective in identifying some silent heat cows which fail to show other obvious signs of estrus. This heat detection assistance tin be constructive if used in a herd surroundings where the devices are checked twice daily, excessive time is not devoted to cleaning mud and manure from them to observe the readings, and cattle are non agitated or moved excessively. Changes in management activities that prompt excessive moo-cow activity on certain days can crusade inaccurate readings.
Estrous detection in the hereafter may involve electronic monitoring of mounting activity, walking, or vaginal electrical resistance integrated into an automatic telemetric system. At present visual observation supported by proper use of conventional heat detection aids is the most effective arroyo to estrous detection.
Glossary of Terms
Anestrus: absence of estrous cycles.
Corpus Luteum (CL): ovarian structure that develops at the site of ovulation during metestrus and continues to produce progesterone through diestrus and during pregnancy.
Diestrus: the period within the estrous wheel when the corpus luteum is functional.
Dominant Follicle: by and large the largest follicle within a wave of developing follicles which eventually suppresses the continued growth of other follicles. Toward the end of the estrous cycle, the dominant follicle becomes the ovulatory follicle.
Estrogens: steroid hormones produced by cells within the follicle. Estrogen induces estrous behavior and muscle contractions with the uterus, oviducts, and cervix. It besides is involved in the initiation of luteinizing hormone release.
Estrous Cycle: the interval between two periods of estrus.
Estrus (Oestrus): menstruum of time when the female is receptive to mounting and will stand up to be mounted by another animal (standing estrus).
Follicle: the ovarian construction which contains the oocyte (egg). As follicles grow, a fluid cavity (antrum) develops. Cells within the wall of the follicle produce estrogens.
Hormone: chemical agents secreted by endocrine glands and transported to target tissues, where they induce or regulate a specific physiological activeness.
Luteinizing Hormone (LH): one of the protein hormones secreted by the anterior pituitary gland and involved in the process of ovulation, corpus luteum germination, and function.
Metestrus: stage of the estrous bicycle beginning immediately after heat. Ovulation and early development of the CL occur during this period.
Oocyte: also termed the egg. Contains the genetic material from the female. It develops within the follicle and is ovulated before long after estrus.
Ovaries: primary reproductive organs where oocytes (eggs) develop inside follicles during the estrous bicycle. Estrogens and progesterone are produced by tissues inside the ovaries.
Ovulation: process of follicle rupture and release of the egg.
Proestrus: phase of the estrous cycle when the CL regresses, progesterone concentrations decline, concluding maturation of the dominant follicle occurs, and estrogen increases. During this stage, some secondary symptoms of estrus brainstorm to be exhibited.
Progesterone: steroid hormone produced primarily by the CL. Progesterone inhibits last maturation of the dominant follicle and the expression of estrus, prepares the uterus for pregnancy, inhibits uterine contractions, maintains pregnancy, and aids in mammary development.
Prostaglandins: serial of lipid substances which produce hormone-like actions. Unlike most hormones, they are produced by many tissues through-out the body. With regard to reproduction, prostaglandin F2a causes regression of the CL during the later portion of diestrus. Prostaglandin is used for synchronization of estrus.
Voluntary Waiting Period (VWP): the interval from calving until the herd director is willing to rebreed the cattle.
Wave of Follicular Growth: a group of developing follicles. Cattle may have two, iii, or 4 waves of follicles that develop during the estrous bicycle.
Prepared by Michael L. O'Connor, professor of dairy scientific discipline
This publication supersedes S282, Rut Detection and Timing of Service.
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Source: https://extension.psu.edu/heat-detection-and-timing-of-insemination-for-cattle