Lifespan will boost profits
Breeding cows and managing
them to ensure your business
will survive was the subject
of a recent Dairy Research
and Consultancy technical
seminar. Jessica Buss reports
GENETIC improvement can be worth an extra £7 a cow a year when bull selection is based on lifespan, calving interval and mastitis, in addition to production, says SAC researcher Jennie Pryce.
Dr Pryce also told DRCs technical seminar in Shropshire that in future, indexes would focus more on production costs rather than output.
"It is possible to gain an extra £21 a cow a year through selecting bulls for lifespan, calving interval and mastitis by progeny testing. PIN currently offers £14 a cow a year average benefit."
The new Profitable Lifetime Index (PLI) for ranking bulls, which replaces ITEM in February, increases potential annual response, and improvements aim to reach the £21 figure, said Dr Pryce.
PLI includes a lifespan score. Each bull with UK daughters is given a score for completed lactations combined with four functional type traits. Younger bulls will have a predicted lifespan score based on type with lower reliability.
This improves on ITEMs longevity predictions. Because type traits used in ITEM are not strongly correlated with longevity, and make little difference to PIN values, ITEM was slow to be accepted.
Lifespan score, which is incorporated in PLI, can vary from +0.5 to -0.5. The best bulls are worth £38 a cow lactation more than the worst, because fewer replacements are needed and a more mature herd will have a higher average yield.
Future development of PLI may include fertility and health traits, she told seminar delegates.
Fertility was likely to be the next trait to be included in PLI, but more reliable data was needed or a more accurate predictor had to be found.
Effect of genetics on calving interval has been studied and there is genetic variation, but it has low heritability and is influenced by management. Dr Pryce explained that daughter groups of 200 were needed for an acceptable reliability score and those animals needed to calve twice, making gathering data time consuming.
But overall fertility could be more easily indicated by condition score, according to Langhill data. "The heritability of condition score is the same as for milk yield and a strong correlation with fertility has been found."
Studies on SACs Langhill herd, where animals are condition scored weekly, show that cow condition score 10 weeks after calving has a high correlation with days to first service and calving interval.
Condition score change from calving to 10 weeks post-calving was less important than condition score at 10 weeks. Actual score at 10 weeks appeared to reflect the animals inherited condition score better. Cow management appears to have less influence on this trait than expected, indicating cows achieve a natural condition score.
"Condition score could, therefore, predict fertility as type predicts lifespan," said Dr Pryce.
But PLI would not include somatic cell count at its launch, said Dr Pryce. "We would have liked to include SCC, but it is economic value is dependent on herd average, so we cannot give it a single value for the whole UK."
SCC, however, offers a good prediction of mastitis. But its economic value is too low to alter PLI values.
• Lifespan included in PLI.
• Condition score could predict fertility.
• Cell count difficult to value.
Improvements to genetic indexes will soon give an economic value for lifespan. Future developments could include using condition scoring to reflect fertility, says SACresearcher Jennie Pryce.