Proper detection of cows or heifers in estrus is the most important factor in artificial insemination programs. This becomes more important where the size of the herd is large as in beef cattle rearing in ranches or big farms. Small holder dairy cattle producers may not experience problems with heat detection because of the small herd sizes which enable the herder to closely observe individual cows and heifers on a daily basis.
Failure to detect estrus early in the breeding season or improper timing of insemination due to heat detection errors results in extended calving intervals and additional semen expense.
Before they are capable of fertilizing the egg, the sperm must undergo a process called capacitation in the female reproductive tract for about six hours. Sperm is viable in the female reproductive tract for just 18 to 24 hours. After ovulation the egg travels rapidly to the oviduct where fertilization takes place. Ovulated eggs remain fertilizable longer (10–20 hours) than they remain capable of being fertilized and developing into normal embryos (8–10 hours). The likelihood of embryonic death increases as the time beyond this interval increases.
Thus viable sperm should be at the site of fertilization awaiting the arrival of the freshly ovulated egg. Breeding either too early or too late allows an aged sperm or an aged egg to interact at the site of fertilization and will result in poor conception. Therefore cattle should be inseminated during the last half of standing heat.
On the other hand, estrus comes about every 18-24 days in sexually mature, non-pregnant female cattle. In detecting these estrus periods you assume the same responsibility as the bull. You must recognize these heat periods to enable proper timing and high conceptions in the cows that are bred artificially. The key point is to accurately identify cows that are in "standing heat" and when the heat occurs. The efficiency with which you do this depends on your skills.
A cow or heifer that allows another one to mount her while she remains standing is the most accurate sign that the animal is on heat. Therefore, the most productive means of determining which cows are in "standing heat" is to observe the cattle carefully for about 30 minutes at least twice per day. More frequent observations may also be beneficial whenever it is practical.
Most cows exhibit signs of estrus at the least convenient time of the day for accurate heat detection. Usually up to 15 percent of the cattle presented for insemination are really not in heat. Poor cow identification is one cause of this problem. It is therefore important to have an elaborate system of identifying animals on heat so that none is missed. The following can be done to improve the success rate of heat detection:
Set up a specific schedule and make one person responsible for observations. Others may be involved in the detection program, but they should report their findings on a specific form or to the individual responsible.
Develop the habit of checking cows at specific times each day. Cows should be watched at least three times daily. While times vary from farm to farm, most cows can be caught in heat if observations are made:
If only two observations can be made daily, watch cows before morning activity starts and after evening chores are finished. Another possibility is to watch at sunrise and sunset if that schedule is more feasible.
Each detection period should last at least 20 to 30 minutes. There will be a substantial variation in the amount of time between mounts for each individual animal. Some cows will be very active with several mounts in 15 to 20 minutes, while other cows will receive only one mount during this time period. Cows that are not very active may have more than 20 to 30 minutes between mounts.
Keep in mind that cows show more signs of heat when other activity is minimal – not at milking or feeding time. Heat detection while cattle are eating at feed-bunks or hay-racks is difficult because hungry cattle are often more interested in the feed than in each other. This fact alone is considered a major cause of heat detection inefficiency. Because of this, the best time to watch for signs of heat will vary from farm to farm. The different periods of observation should be spaced as far apart as possible, since some cows will be in heat for six to eight hours or less.
The time of day that cows show signs of heat may shift due to environmental extremes. In cold weather, more mounting may occur during the warm parts of the day, while the opposite is true in hot weather.
Maintain records so the reproductive status of each cow is known. In larger herds, color code animals to indicate their reproductive status. Use neck tags, neck chains, leg bands and/or chalk. For example, a cow to be bred may have a red neck tag, while a cow that has been bred but not confirmed pregnant may have a green neck tag. For herds with more than one group, cows to be bred should be in one group.
Record all heats, whether the animal is to be inseminated or not. Heat detection will improve if future heats can be anticipated. Use a pocket notebook to record heats and other information. Transfer information to a heat expectancy chart and to the permanent individual cow record.
This permits monitoring of abnormally long cycles and long intervals from freshening to first service. Make a heat expectancy list of open cows or cows that have been bred but not confirmed pregnant. Watch these cows closely, especially the ones that are 18 to 24 days from their last heat period and those fresh for at least 35 days.
Isolate the cow thought to be in heat with a sexually active cow or heat detector animal. Heat may not be detected in some cows in a large group situation, but when isolated with an active cow or heifer, a cow possibly in heat may exhibit standing behavior.
Watch for sexually active groups of cattle. Cows in proestrus or estrus tend to congregate and stay together
Learn how cows in heat behave. In general, a cow that stands firmly when ridden is in heat, unless there is some reason to suspect otherwise. Aside from standing, cows in heat may behave quite differently. Some cows are aggressive in both mounting and receiving mounts and stand for a day, while other cows stand to be ridden for only one to two hours. A small percentage of cows may not stand at all. In observing your cows, it is important to watch carefully since a typical mount may last only 5 to 10 seconds. While secondary signs of heat can confirm heat detection, they can lead to errors in detection if not accompanied by the best sign – the cow standing firmly to be ridden.
Consider using heat detection aids to help increase the number of heats detected. Detection devices and detector animals should supplement routine visual observation.
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