26 November 1999


By Jessica Buss

REDUCING calving to conception interval by an average of 15 days is possible using a synchronised breeding regime, despite a lower pregnancy rate to first service. A recent study reveals a possible £50-60/cow average benefit on south east dairy herds.

Researchers at ADAS Bridgets studied 220 cows treated with Intervets Intercept planned breeding regime and an equal number of cows bred normally on eight farms. They found that despite a 10% lower pregnancy rate of 40% (see table), the Intercept-treated cows were all served in the desired period compared with only 70% of the untreated cows.

This reduced the calving to conception interval by an average of 15 days to 91 days for Intercept-treated cows. There were also 6% fewer treated cows barren at 150 days after calving, according to a report in the Vet Record, Nov 6. Most benefit was seen in herds with lower submission rates to first service.

However, results varied in the different herds: Submission rates of untreated cows ranged from 57% to 93% and pregnancy rates to first service were 6% higher to 33% lower in the treated group compared with the untreated group.

Intervets Ian Mawhinney estimates the identified saving in calving interval and cull cows is worth £50-60 a cow in the average herd at current values. But that increased up to threefold for herds with low submission rate for untreated cows and where there was little difference in pregnancy rate between groups.

Costs of treatment will vary depending on the number of vet visits needed to inspect and inject cows, but will not outweigh these potential benefits, he adds.

"Pregnancy rate/service drops with the treatment, but because there is a 100% submission rate more cows are served in a reasonable time."

He recommends the treatment as suitable for herds with a tight calving pattern wishing to breed cows in a reasonable time period – particularly those wanting to im-prove submission rates. "Discuss with your vet how the regime can be used to suit the farm and the cost."

The companys planned breeding programme, Intercept, involves giving cows a gonadotrophin releasing hormone (GnRH), prostaglandin seven days later and then a second dose of GnRH after 48-60 hours. Cows are then served to fixed time AI 68 to 72 hours after the prostaglandin injection. "How-ever, 10% of cows are seen on heat before the final injection and can be served and given the second GnRH dose at the time of insemination."

Many producers are reluctant to induce heat, because lower pregnancy rates mean using more semen. "But with a 10% lower pregnancy rate and semen costing £30 a straw, its only costing £3 a cow in extra semen. For that £3 the cow becomes pregnant sooner and there is less chance of her going barren."

It is also easier to focus on picking up heats of cows not holding to service. "Repeats tend to occur on a 21 day cycle, except for cows that dont synchronise. Then making more effort to look for returns in an 18 to 24 day window can increase heat detection rate." &#42

Fertility parameters of farms using Intercept

Submission Calving to Preg rate Barren at Preg rate Period to

rate conception (1st AI) 150 days (All AI) 1st AI

Intercept 100% 91 days 40% 18% 44% 63 days

Control 70% 106 days 50% 24% 52% 81 days

Difference 30% 15 days 10% 6% 8% 18 days


&#8226 Pregnancy rate lower.

&#8226 Submission rate compensates.

&#8226 Easier to spot returns.