Selection for yield harms functional traits

Improvement in milk production at the expense of fertility is widely accepted on a national level. However management, feeding changes and health status are rarely taken into account, according to The Royal Vet College’s Geoff Pollot.

“Despite gains being made at an industry level in the major dairy traits, few reports exist for the persistent selection for dairy traits in individual herds,” he said. Results from SAC’s Langhill herd, which had been under maximal selection for milk production from 1980 through to 2005 were analysed.

Cows during this period were put to bulls which, at the time, had the highest fat plus protein PTAs. “Despite results from this selection showing an annual PTA increase of 2.60kg for every lactation and an increase in milk production by 35kg/year, there were negative effects on fertility, persistency and cow conformation,” said Dr Pollot.

However, more recently results have indicated a slight improvement in fertility and Dr Pollot believes this is down to work by breeding companies. “Breeding companies have been making decisions about fertility over the past decade and because we were using the best bulls at Langhill, we are starting to see this selection for fertility coming through,” he said.

• For more from this week’s BSAS conference see next week’s Farmers Weekly.