15 October 2011

4 minute read

Consequently, the UK, has moved from Profit Index (£PIN) which was totally production based to Profitable Lifetime Index (£PLI) which also includes non-productive traits such as fertility, lifespan and somatic cell count.

Genetic trends in dairy cows have been for increasing milk production but this has led to declining genetic merit for butterfat and protein per cent, fertility and lifespan. Infertility is estimated to cost the average 100-cow herd around £22,000 per year and is the primary reason for dairy cow culling.

However, when selecting AI sires, many farmers do not take account of sire fertility index, despite the fact that DairyCo has published it with sire proofs for over five years now.

This is the message from Marco Winters, head of genetics for DairyCo Breeding+ who highlights that: “There is a need for farmers to gain a better understanding of breeding and sire selection so that a clear breeding plan can be established.”

"As farmers have used bulls with higher and higher Predicted Transmitting Abilities (PTAs) for milk production, their PTAs for calving interval have got worse. In other words, they've got longer," says Mr Winters.

“However, since 2005 when the Fertility Index was first launched, selection continued to favour milk production but the genetics for calving interval started to improve. This is excellent news, because it tells us that it’s possible to continue breeding for better production without sacrificing fertility and offers the realistic hope that future improvements can be made through breeding.”

To investigate the practical impact of sire fertility index on daughter fertility, Dr David Mackey of CAFRE has retrospectively analysed the fertility records of Greenmount’s Future Herd and several other pedigree and non-pedigree herds throughout Northern Ireland.

“While it takes data from a lot of cows to demonstrate genetic trends, the benefits of selecting sires with a positive fertility index can be clearly seen through both a reduced calving interval and an increase in conception rate.”

Dr Mackey goes on to comment that: “Had we know that some of the sires used before 2005 carried a negative Fertility Index, they would not have been selected. Since then only bulls with a positive Fertility Index are selected and we should start seeing the benefits of this in the next few years.”

A number of dairy farmers in Northern Ireland actively use £PLI in their sire selection each year and see the benefits of it, including Drew McConnell from Newtonstewart, Gary McHenry from Lurgan and Kenneth Montgomery from Eglinton.

Drew comments that he “Always selects bulls on £PLI, ideally those with a £PLI of £180 or more,” but goes on to say that “they need to have positive milk figures and positive fertility as well.”

Analysis of Drew’s breeding records established that, on average, each one-point increase in a sires Fertility Index reduced the average calving interval of his daughters by almost a day, twice that estimated by DairyCo (0.5 days).

This demonstrates the benefit of including positive fertility in your sire selection criteria. Drew also says that “I cull a lot of cows for mastitis and I’m trying to address this through breeding by selecting bulls with a negative SCC score.”

Similarily, Gary McHenry focuses on £PLI as a simple and effective screening tool.

"As we already have the genetics to produce 9,200 litres, our focus isn’t so much on milk yield but on protein percentage, fertility and somatic cell count.

"We only look at bulls with a PLI of £150 or more, and then select bulls with protein percentage above +0.10 per cent, fertility index above five and SCC less than - 10. These traits are all heritable and will contribute to higher profitability in future.”

Mr Winters comments: "Farmers like Drew and Gary who are paying attention to and adopted the strategy of selecting on fertility are to be congratulated, and the AI companies have played an important role in the process through the increased listing of positive fertility bulls in their catalogues.”

However, fertility isn’t the only non-productive trait considered within the £PLI index. Bulls also carry proofs for Lifespan and Somatic Cell Count, and these should also be considered when selecting bulls.

Mr Winters suggests that "Sires should be screened on £PLI in the first instance, and then check the fitness traits important in your herd and ensure you are using bulls that have strengths in the right areas.

For many herds, the area which will need particular improvement is fertility, and today, it's possible to find more bulls on the market than ever before which will transmit good fertility on to their daughters."