Consequences of Inaccurate Heat Detection

Heat detection rate is the most critical factor for achieving successful reproductive management. Dairy producers realize the importance of improving heat detection rate and its effect on pregnancy rate. Pregnancy rate is the percentage of eligible cows to become pregnant during a given time period that actually do become pregnant. The benchmarks for heat detection rate and 21-day pregnancy rate should be 65% and at least 20%, respectively. Herd management computer programs and DHIA reports summarize heat detection and pregnancy rates. These indicators should be monitored frequently to assess whether goals are being achieved. Unfortunately, for various reasons the accuracy of heat detection is a problem on numerous dairy operations. Several research studies using milk progesterone analysis documented that between 5 and 30% of the cows inseminated are not in estrus. One study conducted in seven northeastern states revealed that 5% of the cows inseminated were not in or near estrus when inseminated. Although that is not excessive error rate, over 30% of the herds had an error rate above 10%. This is indeed a problem. The consequences of inaccurate heat detection are as follows:

• High services per cow and decreased 21-day pregnancy rate
• Excessive use of semen
• Potentially an increase in the incidence of uterine infections. Cows inseminated when not in estrus are likely in the luteal phase of the estrous cycle when the uterus is more susceptible to infection.
• Inaccurate records - due to incorrect heat dates being recorded, dates for subsequent heats will be incorrectly estimated.
• Frustration for everyone involved with the reproductive management program

The majority of the errors are due to cows inseminated based upon secondary signs or incorrect signs of estrus. In an attempt to improve heat detection rate, it is human nature to be aggressive and inseminate cows on any clue the cow is approaching or in estrus, even a passionate look in the eye. Unfortunately this causes the problems outlined above. The error rate can be reduced when the criteria for determining onset of heat is restricted to the primary sign of heat, "standing to be mounted". As herd size continues to increase, it is important that all employees understand the essentials of heat detection and adopt practices that reduce errors. Standard operating procedures (SOP) can be used effectively by herd managers to improve the accuracy and efficiency of heat detection.

Producers using timed breeding programs may wonder why these programs are effective when many cows are inseminated without exhibiting standing behavior. The protocols for these programs are designed to synchronize regression of the corpus luteum, development of the dominant follicle and ovulation so that insemination is performed at the most optimal time for a group of cows. Many cows do not exhibit heat because the last injection of gonadotropin-releasing hormone (GnRH) releases luteinizing hormone (LH) which causes ovulation but also "shuts down" estrogen production by the follicle. Consequently, in this situation, estrogen production is not maximized and estrus is not exhibited. Remember timed breeding programs are designed to increase the submission rate (theoretical heat detection rate) to insemination so groups of cows are inseminated in a timely manner with acceptable conception rates.

Heat detection programs using visual observation are effective if adequate time is devoted to frequent observation for heat, when and where cows are likely to exhibit heat and insemination is based upon the primary sign of heat.