AI synchronisation may leave bulls redundant

21 April 2000

AI synchronisation may leave bulls redundant

By Jessica Buss

BEEF farms may soon stop keeping bulls, and use better genetics, with improvements in synchronisation practices resulting in 90% of cows pregnant to AI in 47 days.

SAC researcher Basil Lowman would like to see pregnancy rates from triple synchronisation increase to 94% in the 120-cow trial herd at SAC Edinburgh. Then synchronisation without any bulls on farm could become commercially viable.

With attention to minor details, he hopes a 94% pregnancy rate will be achieved when cows are served this spring.

However, trial vet Colin Penny, of the Royal Dick Vet School, Mid Lothian, believes that a 90% pregnancy rate is better than many commercial herds achieve using natural service in a 47-day serving period.

Many producers also underestimate the cost of keeping bulls, says Dr Lowman. "A 100-cow herd is often quoted as needing three bulls for natural service. But few run one bull with 35 cows, most have more."

Synchronising cows for serving with AI once can reduce the bulls needed to two/100-cow herd. Typically 60% can hold to AI, leaving 40% to be served by bulls. But with six cows likely to be barren, each bull only gets 16 cows pregnant.

"So if you synchronise cows once, bull cost for each cow served can go up."

Using AI means all calves can be of top quality and replacements bred selectively from some cows. Its possible to select a Limousin sire for Aberdeen Angus cows or vice-versa as they come in for AI.

"Bull semen for AI is also checked for disease, which is important when breeding replacements," adds Dr Lowman.

To use AI needs labour intensive heat detection over a long period, or synchronisation of oestrous.

However, pregnancy rate to first AI after synchronisation using progesterone releasing implants, such as the CIDRs used in this study, is often only 55%. But in the study this has been improved to 63% using oestradial and pregnant mare serum gonadotrophin (PMSG).

Cows are given an oestrodial injection at the same time as the inter-uterine progesterone implants, costing about £1/cow. Thin cows or those which will be less than 55 days calved at first AI are given PMSG to ensure they cycle, costing £2/cow.

This higher pregnancy rate makes multiple synchronisation more viable in practice. But there are also additional costs of using more progesterone implants.

However, reusing these implants after insemination offers the potential to synchronise a second heat for those cows not holding to AI, says Mr Penny. The implants appear to have enough progesterone left to achieve this and it doesnt do any harm when cows hold to service.

After their initial use implants are disinfected and dried, so minimising disease risks. Then 16 days after AI they are re-implanted. This use is outside data sheet recommendations, so there can be no quibble with the company if they dont work, explains Mr Penny.

"The aim of re-using CIDRs is to tighten up returns to service; if they werent used cows would come in heat over a spread of 18-22 days. Leaving the implants in until 21 days after service stops them returning early."

Then cows are served to observed heats. Its not possible to use fixed time AI, as after the first synchronisation, because pregnant cows shouldnt be served again.

In the study, 82% of the cows were pregnant after a 23-day service period.

Cows served a second time are given a new CIDR 16 days later, and heat detection starts again for a few days when these are removed.

With CIDRs costing £8-10 each and an average of 1.3 used a cow, Dr Lowman believes the costs of triple synchronisation will compare well with buying high quality bulls for natural service. &#42


&#8226 First service conception 63%.

&#8226 94% pregnant in 47 days.

&#8226 Bulls may become redundant.

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