29 September 1995

Calving interval alone just not on

MILK producers who rely only on calving interval (CI) as a guide to fertility are wasting their time.

Instead Dr Dick Esslemont of the University of Reading advised considering CI alongside culling rate and failure-to-conceive (FTC) culling rate.

"The UK culling rate is 23% a year with virtually no animals sold for sensible reasons such as low yield or old age," he said. Over 40% of animals were culled due to poor fertility and loss of herd replacements from birth to calving was 28% – partly due to poor fertility management of bulling heifers.

"One could say that the national dairy herd is leaking resources at a high rate."

Dr Esslemont has devised a score known as Fertex to measure profit lost through poor fertility.

It reflects the cost of an extended CI (over 368 days); a high FTC culling rate (over 6%); and an extra service a conception (over 1.9 a cow).

"Every extra cull sold costs £770 in profit not made, the extended calving interval £3 a day on average and the extra insemination costs about £20," he said.

Dr Esslemont cites results of a RSPCA-supported study of 90 DAISY recorded dairy herds.

The average herd had a Fertex score (lost profit) of £78 a cow based on an average CI of 380 days, average FTC culling rate of 9.6% and services a conception of 2.1 a cow. He said the worst herds surveyed were losing £140 a cow against only £23 a cow for the best 10% herds.

Heat detection rates averaged 55% (top farms were achieving 70-80%) and pregnancy rates 46%.

"These figures are concerning – heat detection rate has stuck at 55% for the last 20 years and pregnancy rate has fallen from 53% in that time," said Dr Esslemont.

He advised serve 90% of calved cows; securing an average interval to first service of less than 70 days; and achieving heat detection rates above 58%.