CALVING INTERVAL is a poor measure of dairy herd fertility performance, it is far better to use pregnancy rate and a pregnancy inventory, says ABS Global vet Neil Michael.

Dr Michael, from Wisconsin, USA, told delegates that calving interval gives no indication of fertility performance in the past month. “You need a measure that is more sensitive than calving interval or days open.

” He uses five measures to monitor performance, but his top two are pregnancy rate and pregnancy inventory. He defines pregnancy rate as how many cows are pregnant of those that were eligible to become pregnant in a 21-day period. It differs to conception rate, which only takes into account cows served.

Pregnancy inventory will be new to many in the UK, he added. “It shows whether the number of cows due to calve in each week is sufficient to sustain herd size and cashflow in all-year-round calving herds.

” In the USA, the average pregnancy rate for 62,000 cows was just 16%, he said. But those using the ABS Reproductive Management Service have an average pregnancy rate of 19%. Genus in the UK recently launched the same service, in which technicians monitor cow activity.

For each 1% rise in pregnancy rate, Dr Michael said the benefit was an increase in profit of 9.57 a cow each year or 4438 for a typical UK herd.

STANDING TIME

Another factor often reducing fertility performance by up to 3-4% is excessive time spent standing up, believes Dr Michael, who recommends actually measuring time spent on concrete.

“Cows should spend half their time lying down, producing milk.

” An audit of time on concrete takes three to four hours, as it is important to know the time between opening the gate for high yielders at milking and when it is closed. That is multiplied by the number of milkings. Ideally, this should not exceed three hours a day, he said.

The total time cows spend on concrete should not exceed 12 hours a day. And checking how many cows are lying down 2-4 hours after milking will indicate cubicle comfort.