That is cows recorded as being on heat the previous evening and the current morning all get inseminated that morning, as this will limit the proportion of cows which are inseminated too late.Īlthough it is often suggested as an option when fertility is poor, inseminating once-a-day is not just effective when you have poor heat detection and low conception rates. If the proportion of cows submitted is low, because of relatively poor heat detection or cows not showing heat intensely, or if two periods of dedicated heat observation per day are not feasible, then the 'am/am and pm/am rule' may produce the best results. When determining the answer to when to inseminate, the first question to ask is: how good is heat detection? If there are two periods of targeted observation for heat detection every day AND the proportion of cows submitted is relatively high, then the am/pm rule is likely to still be optimum, with recent research showing that insemination 12 hours after the start of oestrus activity still results in the best conception rates. The ideal time for mating is at the end of oestrus (or about 12 hours after it starts). However, the modern dairy cow shows heat less intensely (fewer than 50% of cows in oestrus stand to be mounted compared to >70% in the 1980s) and shows it for a shorter period of time (duration of standing oestrus has decreased from an average of 15 hours to 5 hours), so the question is often asked as to whether the am/pm rule needs to be changed.įigure 2: Oestrus behaviour starts around 24-32 hours before ovulation. This research led to the development of the 'am/pm rule' - where a cow which was seen on heat in the evening was inseminated the next morning, while a cow that was seen on heat in the morning was inseminated the following evening. The use of devices such as Kamars better identify heat and thus mean the timing of insemination can be more accurate. Figure 1: Accurate heat detection is crucial to the timing of insemination.
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