27 September 1996

Fertility traits could be in sire selection listing

Genetic selection for fertility will help achieve a 365-day calving interval, last weeks Nottingham Fertility Conference heard.

Jessica Buss reports

DAIRY producers could in the future add fertility to the list of traits on which they base sire selections when breeding replacement heifers.

That is provided research at Nottingham University lives up to early expectations. Work here has shown that the time it takes for a cow to start cycling after calving is related to her sire. And that early cyclicity leads to improved fertility.

Speaking at the Nottingham Fertility Conference researcher Melissa Royal said: "Fertility could be included in sire proofs without compromising selection for milk yield."

Initial studies show that onset of cyclicity after calving is as heritable as milk yield.

"There is much variation of this trait within sire families," she said.

Sire families from 10 bulls were analysed using milk progesterone profiles taken from 81 cows to indicate oestrous activity. Cows from these different sire families averaged from below 20 days to above 45 days to return to a normal oestrous cycle after calving.

The average cow in this study started cycling at 30.5 days post-calving with 66% within 15 days either side of this.

"Those animals that started cycling late had 50% pregnancy rates," said Miss Royal. "Those that started early had a pregnancy rate of 62%."

But in this early trial only six sires had enough daughters to assess heritability; these showed the "onset of activity" trait to be 32% heritable.

Within the next year cycles of 650 cows from 65 sires will have been analysed. If the 32% heritability rate is confirmed then progesterone milk testing a small number of bulls daughters would produce viable rankings for sire proofs.

Because average daily yield was not a factor influencing the return to cyclicity, Miss Royal says that it will be possible to identify high production bulls that produce fertile cows.

The Nottingham University Cattle Fertility Research group will receive £800,000 from MAFF and MDC over the next five years.


&#8226 Fertility is a heritable trait.

&#8226 Sire families vary in fertility status.

&#8226 High production bulls that produce more fertile cows can be identified.


FERTILITY SELECTION

The earlier this cow starts cycling after calving the more fertile she will be, says Nottingham Universitys Melissa Royal.