Look to arrest decline in dairy cow pregnancy rate

2 April 1999

Look to arrest decline in dairy cow pregnancy rate

For dairy, beef, sheep or pig

producers, there was plenty

of new research and

practical information at last

weeks British Society for

Animal Science conference

in Scarborough, Yorks. The

livestock team was there to

gather the news

DAIRY cow pregnancy rates have fallen by 1% a year in the UK since the early 1970s, from 56% to 39%, and producers need to focus on halting, if not reversing, this decline.

That was the message of Melissa Royal of the University of Nottinghams cow fertility research group, speaking at BSAS. She estimated that the current average pregnancy rate was about 44% for animals inseminated at the correct time in their heat cycle.

Her studies compared two milk progesterone testing databases, one collated between 1975 and 1982, and the other between 1995 and 1998.

It appears that there is a 24% rise in abnormal hormone patterns produced by todays cows. This is mostly reflected in delayed degeneration of the corpus luteum, meaning cow do not come on heat as quickly, so delaying breeding.

This decline in fertility has occurred during the period when Holstein genetics were introduced, yields have increased from 4270kg in 1975 to 5515kg in 1996 and nutrition has changed. While these factors need investigating, it is too early to claim these are causes of poorer fertility, she said.

"In the short term early identification and treatment of these conditions will help." Milk progesterone testing three times a week for a 20-day period could help identify problem cows.

The way forward is to look for animals prone to these conditions to identify any genetic variation, she added. Then see whether there is sufficient heritability to introduce a fertility measure into breeding programmes.

"Fertility is not included in sire selection programmes today, but parameters such as condition score are being investigated at SAC," said Miss Royal

SAC Edinburgh geneticist Jennie Price believes the decline in fertility is genetic. That is the conclusion of a recent study of data from 900 maiden heifers introduced into SACs Langhill Herd over the past 16 years.

"For every extra 10kg of fat and protein animals are selected for, expect a one-day increase in the interval between first and last service," said Dr Pryce.

A review of maiden heifers found there was a small but definite difference between fertility of animals selected for higher genetic merit and control animals.

While genetic merit of control animals increased in line with the UK national herd, the selection line increased at a much faster rate. Every year four bulls were selected for use in each of the groups, reducing sire effects.

The most reliable difference was seen in the interval between first and last service. She also noted differences in conception rates. Control heifers had a conception rate of 45%, whereas for selection animals it was 39%.

"If the relationship between cow and heifer fertility is proved to be strong, using a measure of fertility in a progeny testing scheme could help reduce the fall in fertility." Previous studies by Dr Pryce indicate that condition score may be a useful indicator of fertility, which could be used in breeding indexes.

SACs Geoff Simm added that many producers believed that selecting for increasing yield meant better food intake and fertility would follow, but it did not appear to be the case.


&#8226 Declining 1% a year.

&#8226 Believed to be genetic.

&#8226 Progesterone testing could help.

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