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Cattle

The use of fixed time artificial insemination programmes for the use of sexed semen in block calving dairy heifers

02 May 2021
Clinical
13 mins read
02 May 2021
Volume 26 · Issue 3
Figure 1. Heifers at grass during breeding season.
Figure 1. Heifers at grass during breeding season.

Abstract

In seasonal block calving herds reproductive efficiency can have a significant impact on productivity and profitability. Within this it is key that the nulliparous heifers calve down promptly in the block, and if these heifers can have heifer calves it will expediate genetic gain. There is extensive research into the conception rates of differing protocols and the literature is reviewed to support the choice of protocol used in the subsequent case study. The case study uses a 6-day progesterone protocol with two injections of prostaglandin F2α and sexed semen; it demonstrated acceptable conception rates as well as the variability that can occur between different bulls' semen straws. Finally, the case study assesses the costs and benefits of the synchronisation programme and concludes a cost benefit of £88.55 per heifer.

In block calving seasonal herds, the 6-week pregnancy rate is a key measure of reproductive efficiency. Maximising the number of heifer calves born to provide replacement animals accelerates the herd's genetic gain. Coinciding the heifer group's calving period with the start of the herd's calving block is advantageous for several reasons. First, the replacement heifer calves born will be uniform in age for the rearing period, and second, they will be a minimum of 24 months old at their first calving. Calving heifers early or before the main herd's calving season also allows these dams to have a minimum of 90 days before the start of the herd's next breeding season.

However, inseminating nulliparous heifers, particularly in pasture-based spring calving systems, can have practical difficulties, with the heifers being at pasture during the breeding season (Figure 1). Synchronisation programmes that allow for fixed time artificial insemination (FTAI) can be very efficient mechanisms of obtaining the aforementioned desired goals, even more so if sexed semen is used, thereby maximising the number of heifer calves born.

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heifer FTAI
seasonal block calving
synchronisation
cost benefit