Heat detection efficiency

Feb 20, 2009
by WLJ
Heat detection efficiency

Heat detection efficiency (rate) is defined as the percentage of eligible cows that are actually seen or detected in heat. Several methods of calculating the efficiency with which heat is detected are available. A detection rate of 80 to 85 percent should be achievable. The detection rate can be measured by the 24-Day Heat Detection Rate Test, which is a test that the producer can implement to self-evaluate the heat detection efficiency (or inefficiency).

In order for cows to be included in the test, they should be those eligible to have heat cycles, at least 30 days post-calving for dairy or 50 days post-calving for beef cows; be free of reproductive disorders such as cystic ovaries, pyometra, or other reproductive tract infections; and be nonpregnant.

What is wanted is a group of cows most likely to display estrus in the next 24 days. Some of these cows will, in fact, be serviced during that interval, which will exclude them from the next 24-day list. At the end of the 24-day period, the number of cows detected in heat is divided by the total number of cows eligible to have estrous cycles. If the producer observed 50 cows but only 15 were detected in heat in 24 days, that is a 30 percent detection rate—not too good! If the producer finds 40 or more cows in heat during the 24-day test period for 80 percent or better detection rate, then a good A.I. program is possible.

A second method of selfevaluation of heat detection can be performed by keeping an accurate record of heat dates. The average interval (in days) between detected heats is divided into the “expected” interval, or 21 days. For example, if the average interval between detected heats for all eligible cows is 25 days, then the detection efficiency would be computed at 21/25, or 84 percent. — Glenn Selk, Extension Specialist, Oklahoma State University