In This Section |
Maximizing Conception Rate in Dairy Cows - 1. Heat Detection
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Measure of Performance
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Goal
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Needs Improvement
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| Avg interval from calving to 1st heat |
40 days
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60+
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| Avg no. days to first service |
70 days
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90+
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| Avg no. days open |
100 days
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120+
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| Avg calving interval |
12.5 mo.
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13+
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| Avg no. services per cow |
1.72
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2.0+
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| % cows checked in calf after one service |
60%
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less than 50
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| % of herd culled for reproductive reasons |
5%
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10+
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| Age at first breeding |
15 mo.
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17+
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Calving interval is the most important overall measure of herd performance. Delayed first breeding has a direct effect on lengthening calving interval.
Missed heats or failure to detect heat signs is the number one reason for long calving intervals. Recent studies indicate that 85-90% of the variation in days open is caused by differences in heat detection and only 10-15% is due to differences in conception rate. Fifty to 60% of heats may be missed in problem herds.
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Identify all cows and heifers by name, number, ear tag, neck tag or any other means of positive identification with which everyone on the farm is familiar. It may also be useful to tag or mark groups of animals, for example those that are open, and those that are confirmed in calf.
Record each calving date and all reproductive activity. Record systems can include: 21-day calendar, breeding wheel, booklets and file systems as well as computer systems. The heat and breeding dates must be recorded and other symptoms such as signs of blood, mucus discharge, should be recorded as well. Record the first heat after calving as well as all subsequent heats.
Records must be kept up-to-date. They must be easy to use and available to all farm staff, the veterinarian and inseminator. Some dairymen use a heat detection report card whereby a card is filled out for each heat detected. Other symptoms can be recorded on the same card.
An essential part of any record system is a 21-day calendar which can be obtained free from any AI Stud. It should be displayed in a prominent place in the barn. When kept up-to-date, it gives at a glance a prediction of cows that should be checked for heat signs.
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To detect heats accurately the dairyman must have a basic understanding of the estrous cycle of the cow. The estrous cycle is a period of time when orderly changes occur in the cow's reproductive organs, hormone levels and sexual behaviour. The most important of these events are:
The estrous cycle in a normal, healthy cow is on the average, 21 days, ranging from 17 to 25 days. The cycle of virgin heifers may be 1 or 2 days shorter. Although a few normal cycles occur outside this range, most that do are abnormal and associated with infertility.
The estrous cycle is controlled by hormones. It is important to know how the estrous cycle operates to detect heats properly, identify problem cows, and make wise use of modem drugs such as prostaglandins.
During the estrous cycle, Follicle Stimulating Hormone (FSH) is secreted into the bloodstream by the pituitary gland located at the base of the brain. FSH causes follicles in the ovary to develop and grow in waves at 4, 10 and 16 days in the estrous cycle. A single follicle that develops late in the cycle continues to grow and produce estrogen which causes the signs of heat. It will mature and ovulate - releasing a mature egg, just after the period of standing heat (estrus).
The changing levels of estrogen cause the release of Gonadotropin Releasing Hormone (GnRH). GnRH causes the release of Luteinizing Hormone (LH) by the pituitary about 2 hours after the start of standing heat. LH causes ovulation to occur 24 to 36 hours after the start of standing heat. The newly released egg passes into the open end of the oviduct and travels toward the uterus. If insemination takes place at the proper time, fertilization will occur partway along the oviduct.
After ovulation, the follicle wall collapses and the corpeus luteum (CL or yellow body) is formed by the cells lining the empty follicular cavity. The CL begins to secrete progesterone. Progesterone prepares the uterine wall for implantation of the embryo and maintains the early part of pregnancy. If the cow is not pregnant, prostaglandins produced by the uterus, breaks down the CL, progesterone production stops and the cow comes back in heat again.
If the cow is pregnant, the CL remains and continues to produce progesterone to maintain the pregnancy. A milk sample taken at day 23 after breeding can be analyzed for progesterone level. This will indicate whether or not the cow is pregnant. The Progesterone Testing Service is operated by the University of Guelph. Sample kits are available from the Ontario AI Studs, as well as the University of Guelph.
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Standing to be mounted is considered the primary sign of heat. Most cows show increased sexual activity before estrus or actual standing heat. Secondary heat signs indicating a cow is near estrus include:
The expression of secondary heat signs shows a great deal of variation among cows. A few or all of these signs will be exhibited 6 to 24 hours before true standing heat. These signs should be noted and the cow watched more closely for standing heat in the next few days.
Figure 1. Signs of heat.
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The only accurate indication of when to breed a cow is true standing heat. This is when a cow will stand to be mounted by another cow
The actual time of standing heat is short. Cows will show standing heat for an average of 10 hours. Twenty-five percent of all heat periods, however, last less than 8 hours. Many cows come into heat at night. The largest group of cows (70%) actually come into heat between 6 p.m. and 6 a.m.
Work done with continuous observation of cows at the University of Guelph also indicated that cows that come into heat between 1 a.m. and 7 a.m. have short heat periods. Of this group, more than 50% showed standing heat for less than 8 hours.
Mounting activity increases as the number of cows in heat at one time increases. There may be only 11 mounts with one animal in heat compared to up to 50 mounts when 3 animals are in heat. Some natural estrus synchronization may occur within groups of cows. On certain days there might be more than one cow in estrus, and then, blocks of days when there are no cows in estrus.
Heat detection should be carried out two to three times per day to accurately detect cows in standing heat. Table 2 shows that 3-times-a-day observation will detect more than 90% of all heats whereas once-a-day observation will only detect 60%. Time spent observing cows should be at least 20 minutes. Slowly walk through the group of cows once during the observation period to cause them to move about, and possibly show better heat signs.
| No. of Observation Periods | % Cows Seen in Heat |
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| Once-a-day observation | 60% |
| Twice-a-day observation | 80% |
| Three-times-a-day observation | 90% |
| Four-times-a-day observation | 100% |
Good foot care is critical to cows showing good mounting activity. As well, exercise areas and walkways should have good footing. Grooving or scabbling of smooth concrete surfaces is recommended.
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First heat occurs at 14 to 22 days after calving. Signs of heat are poor at first heat. Heat signs and conception rate improve until the third heat occurs at 50 to 60 days. For best results, plan to breed cows starting at 50 days after calving.
The sperm and the egg have limited lifetimes in the female reproductive tract; therefore, timing of insemination is important. The best time to breed is 12 to 24 hours after the onset of standing heat. When cows are checked for heat 2 or 3 times daily, the onset of standing heat can usually be determined.
Figure 2. Standing to be ridden is the only reliable sign of when to breed a cow. A cow should be bred 12 to 24 hours after the onset of true standing heat.
Cows first seen in heat in the morning should be bred late in the afternoon. Those first seen in heat in the afternoon or evening should be bred the next morning.
In calling for early or late technician service, the farmer must have observed the cows frequently to determine the start of standing heat. Proper identification of when a cow is actually in standing heat is usually more critical than once or twice daily calls from the technician. In problem herds, 30% of the cows ,may be bred in the wrong stage of the estrous cycle - when they were not in heat at all.
Watch cows closely for signs of heat after breeding. A cow showing standing heat the day after breeding probably should be bred again the next day. A bloody discharge will show after standing heat, about 12-30 hours after breeding. Not all cows show an obvious bloody discharge. The presence of a bloody discharge is no indication of whether or not the cow is pregnant. It is a good guide whether the timing of the insemination was correct or not.
If a cow has not been observed in heat but shows a bloody discharge, she should be marked on the 21-day calendar to watch for heat in 18 days' time.
Figure 3. Time to breed cows for best fertility.
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Prediction of upcoming heat periods is very important to accurate heat detection. Twenty-one-day calendars, breeding wheels, and computer record systems help predict heat periods when used on a daily basis. The most effective system is one that is used every day by those responsible for heat detection.
Heat mount detection aids or devices are an aid but not a replacement for good reproductive management.
Heat mount detectors (Kamar) are pressure-sensitive devices that can be glued on the rump of cows to be checked for heat. When a cow in standing heat is fully mounted by another cow, the pressure causes a color change in the dye capsule in the heat-mount detector. Cows can also be marked with special paint or grease pen. Mounting activity will wear off or smear the marked area.
To be effective these devices require special management:
Heat Detection devices are especially effective with heifers or problem breeders. Heat detection can be 90% with once-a-day observation but very low without regular observation.
Heifers that have been treated with hormones or a bull with a surgically altered penis can be used to detect cows in heat. A treated heifer or cow is preferred due to ease of handling compared to a bull.
The detector animal must be fitted with a chinball marker, or Kamar detector must be used on the cows for heat detection. With once-a-day observation, this system can detect 90% of all cows in the herd that are in heat.
Detector animals will stimulate increased activity, seek out cows in heat, mount them and mark them. A ratio of 30 cows to 1 detector animal is preferred (50:1 maximum). Cows in heat that have been identified should be removed from the herd so that detector animals can seek out new cows.
Other aids to heat detection have been tested but are not in common use. Television cameras hooked up to a monitor in the house or office can be of assistance in watching for cows in heat, and extend the times at which the cows can be observed. A vaginal probe can be used to measure the drop in electrical resistance of vaginal secretions during estrus. Pedometers measure the cows activity which increases by 2 or 3 times at the onset of heat. Changes in milk temperature, milk production, and feed intake may be useful in predicting onset of standing heat.
These measures are helpful as they can be monitored electronically; however, they have not as yet replaced observation of a cow in standing heat as the best indication of when to breed that cow.
Prostaglandins are naturally occuring compounds that cause destruction of the corpus luteum and bring on estrus. Use of prostaglandins between day 5 and day 17 of the, estrous cycle, when there is an active corpus luteum, will bring on estrus 3 to 4 days later. Cows will not respond to prostaglandin at other times of the cycle when there is no functional CL.
Prostaglandin injections can be used to synchronize estrous cycles, plan the timing of the breedings, to aid in heat detection, and in treatment of some disease conditions. Prostaglandins do not improve fertility in normal, healthy cows but they do change the time that estrous occurs. They should be used only on consultation with a veterinarian.
Two common methods of using Prostaglandin:
It is better to breed on heat signs after prostaglandin injections. The response of some cows to the injection varies. Arbitrarily breeding at 72 and 96 hours after injection may not be as successful as breeding on actual heat signs.
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The following points summarize what is necessary for a good heat detection system:
This Factsheet was prepared with the assistance of Dr. Frank Hurnik and Dr. Gordon King at the University of Guelph and members of the OMAFRA Dairy Advisory Team.
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