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A UK Fertility Index For Dairy Cattle
Published: Mon, 05 Sep 2005
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Research Note Full Title
Developing a UK fertility index
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On-farm conception rates in the UK have been declining at a rate of 1% per year over the last 20 years. One reason for this decline is thought to be breeding, due to an unfavourable genetic relationship between yield and fertility. Since genetic selection for yield has partly contributed to this decline in fertility, control of fertility through genetic selection will in the long run offer a sustainable solution. This requires a means by which milk producers can select for bulls with fertile daughters, thus prompting the development of the UK’s first Fertility Index.
Objectives
The objective of the project was to use nationally recorded data to estimate bull proofs for daughter fertility.
Outcomes
Achievements
The study confirmed the genetic correlation that improved milk yields lead to poorer fertility. However, this it was not a "one for one" relationship, suggesting that there is scope to include production and fertility together in balanced selection decisions. A strong relationship between all fertility traits was also found, suggesting that improving one will lead to improvements in the others. Bull proofs show sufficient genetic variation in fertility to allow improvements to be made in fertility. Fertility traits were combined in an index, weighted by their economic weight.
The graph (see figure) shows that bulls compared on their £PLI ( the current UK dairy selection index) and the fertility index. There is substantial variation in fertility amongst the top bulls. There are good production bulls available with good fertility.
Implications
The fertility index allows breeders to choose from within the available good production bulls, those that have the overall best match of traits for them, including fertility. More importantly, breeding companies will be able to avoid bulls with large negative fertility proofs as their sires of sons (which only account for a few of the top production bulls). These data will also allow breeding companies to avoid selecting bulls with large negative fertility proofs as sires of sons.
Overall improvement in cow fertility will also be the result of attention to other factors influencing fertility, including feeding, veterinary care and general management. Breeding more fertile cows will provide farmers with the opportunity for increased culling on other traits.