18 September 1998

BEWARE SERVING HERD TOO SOON POST-CALVING

COWS served too early after calving are less likely to conceive and will suffer a higher rate of embryo loss.

SAC Auchincruive researcher Peter Ball says that cows starting to cycle within 25 days of calving are also less likely to conceive, and fertility drugs are often misused.

These are the conclusions from a Milk Development Council funded study on priorities for improving in breeding dairy cows. In trials, oestrus activity was determined using milk progesterone profiles.

According to Dr Ball, there are few cases when serving cows under 50 days calved can be justified. Conception rates below 50 days calved averaged just 43% in SAC studies and embryos were lost in 43% of those conceptions.

"However, in a tight block calving herd when the alternative is to cull a cow, a low conception rate and high embryo loss may be acceptable.

Conception rates

"Generally cows should not be served within 60 days of calving, because conception rates will be too low and embryo losses high," says Dr Ball (see table).

Serving after 60 days post-calving should produce higher conception rates – 49% – and lower embryo loss – 17%. Cows served over 100 days after calving generally have poor fertility or have returned to service, so these figures also show lower conception rates, he adds.

Contrary to popular opinion, cows showing heat within 25 days of calving are not more likely to conceive when served. Cows which start to cycle that soon will probably develop a persistent corpus luteum, preventing normal heat cycles, explains Dr Ball.

Of cows showing ovarian activity before 25 days calved, 37% failed to conceive within 100 days calved, compared with only 18% of cows failing to conceive where activity started later than 25 days calved.

It is, therefore, unwise to serve cows early because they begin cycling early. Methods of delaying cycling will require research, but avoid breeding these cows too early after calving, he advises.

Cow fertility treatments, especially oestrus synchronisation, tend to be over-used. Synchronisation does not increase the proportion of cows served at the correct time. It also results in lower conception rates, and of cows that do conceive, embryo losses are higher than for untreated cows, says Dr Ball.

Infertility

He believes that many cows are treated for infertility because of failure to detect heats. Consider heat detection regimes, record keeping and nutrition management to avoid overuse of fertility treatments, he suggests.

"There is little point in injecting a thin cow that is not cycling with prostaglandin; aim to get her in better condition first," he says.

This MDC-funded study was also supported by Semex, RABDF and Ridgeway Science.

SERVICE SUCCESS

&#8226 Dont serve before 50 days calved.

&#8226 Consider management before vet treatment.

&#8226 Synchronising cows lowers conception rates.

Conception rates and embryo losses by calving to service intervals

Insemination Conception rate Embryo loss

(days post-calving) (%) (% of conceptions)

50 43 43

51-60 49 24

61-70 49 17

71-80 56 20

81-90 59 20

91-100 63 19

100+ 54 16