Improving the Detection of Estrus in Dairy Cattle
R. D. Allrich and R. J. Knutson, Department of Animal Sciences Purdue University, West Lafayette, Indiana
Modern dairy production practices dictate that efficient management techniques be employed in all areas of the enterprise. For example, rations should be formulated to meet all of the nutrient requirements of livestock without providing excess, unutilized nutrients that would needlessly increase costs of production. Another area where increased efficiency will have a positive impact on net income is reproductive management. An important component of reproductive management is estrous (heat) detection, the subject of this publication.
Producers should regard estrous detection as a specific management task. It is often advantageous to assign a particular employee or family member to be in charge of estrous detection, so that one person is responsible for heat checking and recording all heat dates. An understanding of the estrous cycle, knowledge of the signs of estrus, regular visual observation, and accurate record keeping are central to improving efficiency in this area.
This publication first discusses the importance of heat detection and explains the estrous cycle, of which estrus or heat is a part. It then describes 1) the various behavioral and physical signs of estrus in cattle housed in free-stall or pasture environments and 2) the factors that influence the detection of estrus.
The Importance of Heat Detection
In breeding programs which rely on artificial insemination, efficient and successful heat detection protects against extended periods of non-productivity. Inadequate estrous detection leads to missed breeding opportunities or low concep-
tion rates for heifers and cows, which in turn leads to costly extended calving intervals. Improved estrous detection practices allow for heifers and cows to be artificially bred to genetically superior sires and for cows to achieve optimal calving intervals.
It has been estimated that the dairy producer loses $2-4 per day in net income when calving intervals exceed 12.5 months. To maintain the ideal 12.5-month calving interval, cows must be pregnant by 100 days after calving. As a guideline, 90 percent of cows should have been observed in heat by 40 to 50 days after calving. This then allows for approximately three breeding opportunities before the 100 days have elapsed after calving.
A side benefit of the close visual observation required in efficient heat detection is that it is a further means of monitoring the overall health and condition of the cows.
The Estrous Cycle
When they are not pregnant, heifers and cows normally have a 21 -day estrous cycle (range: 18-24 days). In other words, heifers and cows will show signs of heat about every 21 days until they are bred and conceive. After calving, cows normally undergo a 20 to 30 day period when estrous cycles do not occur. The estrous cycle is the result of complex endocrine relationships, but a simplified pie chart depicting stages and time relationships of the cycle is shown in Figure 1.
As Figure 1 illustrates, the estrous cycle can be divided into four stages: 1) proestrus, 2) estrus, 3) metestrus, and 4) diestrus. Proestrus is the stage when follicles on the ovaries attain their
This publication was made possible in part by the Indiana State Dairy Association.
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PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE, WEST"LAFAYETTE, INDIANA 47907
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