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Don’t breed too early

Aurora Villarroel for Progressive Dairyman Published on 18 April 2016

Correct time of insemination is important to ensure conception but also to make sure the embryo has the best conditions to survive long term. An old oocyte has higher probabilities of early embryonic death, and if we breed too early, the sperm may die before the oocyte is ready to be fertilized.

So how then do we determine the best time to breed a cow once she has been detected in heat? To answer this question, we need to look into the duration of certain intervals presented in Table 1 based on published research.



Critical timings for fertilization in cattle

Looking into these ranges, it becomes obvious that the driver of most of the variability is the duration of the actual heat, which is likely a big determinant for conception.

Activity monitoring systems can typically determine how many hours a cow is in heat based on increased activity at the start of the heat and decreased activity when the cow is coming out of heat. On average, cows are in heat for about 12 hours, but there is a range of six to 24 hours, and this variation can happen on the same farm the same day, as shown in Figure 1.

Variation of heat time in four different cows

When new activity monitoring systems are installed, there is a tendency to continue doing things as usual for a while until the personnel becomes familiar with the system and trusts its reports.


During this time, we have observed that most farms tend to breed as soon as they observe a cow in heat which, in the case of the AfiAct II system, shows that many cows are bred right at the time of the start of activity increase (Figure 2).

0716pd villarroel fg 2

When we overlap on the activity graph the ranges for the intervals shown in Table 1, it becomes obvious that most cows are bred too early, leading to the likely situation of sperm dying before the oocyte has even been released. This is an important (and commonly overlooked) factor of poor reproductive efficiency.

It is not good enough to accurately find cows in heat, but it is also imperative to make sure they get bred at the correct time to ensure that live sperm meet with a live oocyte.

This is likely a major reason for some research to conclude that breeding cows twice in the heat cycle improves conception because it allows live sperm to be present at the time the oocyte is released and receptive.

Interestingly, semen companies are also working hard on extending the life of the sperm. Looking at the ranges, the a.m.-p.m. rule makes sense. In this old guideline, cows observed in heat in the morning were to be bred in the afternoon, while cows observed in the afternoon were to be bred in the morning.


This rule, however, has been abandoned in the past few years in favor of breeding only once a day, which has led to breeding cows as soon as possible after being observed to avoid breeding too late.

Most breeders and farmers dread breeding too late. However, a quick look at the lag between heat detection and breeding time in cows that became pregnant to that breeding, clearly shows that cows were typically bred toward the end of the heat, as opposed to the beginning. Cows don’t lie.

An interesting situation observed in farms that have activity monitoring systems is that their unique management such as milking and feeding times, location of the barns in respect to the parlor, number of cows in each pen, slippery floors, etc., affect the activity patterns of the cows and therefore heat detection.

Most cows come in heat between 10 p.m. and 6 a.m. Therefore, a farm that typically breeds at 6 a.m. may be breeding many cows too early in the heat cycle.

It is important to emphasize that every heat detection system is different and they report data differently. Make sure to communicate with the company that makes your specific system to learn how to interpret the data to find the best time to breed your cows.

A system that can be customized to the specific situation of each farm will help fine-tune heat detection and provide the best information to decide what time is the best time to breed on each specific farm.  PD

References omitted due to space but are available upon request. Click here to email an editor.

Aurora Villarroel
  • Aurora Villarroel

  • Application Support Manager, Americas West
  • Afimilk, Ltd.
  • Email Aurora Villarroel