Stillbirths and Calf Survival:

Stillbirths and Calf Survival
By Blair Murray - Dairy Genetic Improvement Specialist/OMAFRA - The percentage of stillbirths has been steadily increasing but you can take steps to improve that rate on your farm.

You'll soon be able to improve the chances of having a live calf on the ground-especially from a first-calf heifer-by looking closely at bull proofs for calf survival rates due to be published in early 2008. Recent numbers suggest that stillbirths have been rising for Canadian Holsteins, although the reasons still aren't clear.

Canadian Dairy Network statistics released last year show that Holstein stillbirth incidence with first calvings has risen to 12 per cent from 10 per cent over the past five years. The stillbirth rate for cows having their second or later calvings is lower at six per cent, but still up slightly from the previous five per cent.

These numbers mean that nearly eight per cent of all calves are born dead or don't survive past 24 hours. However, the statistics don't distinguish whether the reason is due to genetics, farm management or other factors that might indicate why rates have gone up.

Stillbirth data from other parts of the world are similar to Canadian statistics. Earlier U.S. research found that stillbirth incidence increased to 13.2 per cent in 1996 from 9.5 per cent in 1985. Swedish research indicates a stillbirth rate of about 10 per cent in Swedish Holsteins at first calving.

In contrast to these results, a recent Norwegian study of calving difficulties and stillbirths in Norwegian Red cattle found that the frequency of stillbirths was three per cent at first calving and 1.5 per cent for second and later calvings. The rate was unchanged between 1978 and 2004.

In the Swedish study, where Swedish Holsteins had a 10 per cent stillbirth rate, the Swedish Red and White herds reported about half that rate. The Scandinavian red breeds seem to have low stillbirth or good calf survival in common.

Canada, Norway and Sweden define a stillbirth as a calf carried to term, or at least longer than 260 days, and born dead or dying within 24 hours of birth. The U.S. and some other countries consider a stillbirth has occurred within 48 hours of calving. It can be expected that U.S. averages are slightly higher than numbers reported in Canada, Norway and Sweden.

Stillbirth, like calving difficulty, is a much larger problem in first-lactation calving than in later calvings. Incidence in second and later lactations drops to half or less than the rate for first lactations.

The cost to the industry of this many dead calves is quite substantial. In Ontario, with a population of 340,000 dairy cows, about 300,000 calves are born every year. If 30 per cent of the cows are in first lactation, then 90,000 calves are born to them. Reducing the current stillbirth rate of 12 per cent to the Norwegian Red rate of three per cent would produce 8,100 more live calves per year from first calvings. Decreasing stillbirths for second and later calvings to 1.5 per cent from six per cent on 210,000 calvings would result in an additional 9,450 live calves.

That's a total of 17,550 more live calves. If we value a bull calf at $150 and a heifer calf at $400, the total loss or missed potential compared to the Norwegian rate is $4.8 million per year in Ontario.

A Cornell University study published this year paints an even more serious picture. In a study of seven large dairy farms, researchers found that cows having stillbirths had significantly increased risk of culling or death throughout the subsequent lactation. Median days open increased by 88 days compared to cows that had live calves. They concluded that stillbirth losses are far greater than just the value of the calves.

Stillbirth is influenced partly by the calf [direct] and partly by the mother that is giving birth [maternal]. Research has shown there is little or no relationship between maternal and direct genetics for stillbirth, and some studies show a negative relationship. To make any selection progress, we need to look at both traits.

Stillbirth heritability is considered low. The Norwegians found heritabilities of .07 to .08, similar to but slightly less than heritabilities for calving ease. Norwegian and Canadian research found lots of genetic variation, so sire selection to improve calf survival and reduce stillbirths is possible over time.

Norway places only one per cent emphasis on stillbirths in its national selection index. With such a low incidence rate, there would be little value in putting emphasis on improving stillbirth rate. In countries with higher levels, however, calf survival traits should get more emphasis.

Stillbirth incidence is highly related to calving difficulty. According to the Norwegian study, maternal calving difficulty is correlated with maternal stillbirth and direct calving ease with direct stillbirth. Calving difficulty increases the probability of stillbirth, due mainly to trauma and anoxia, a lack of oxygen.

However, research performing post-mortems on stillborn calves has found that half the deaths were not related to calving difficulty. As well, no cause of death could be determined on a third of the calves, which should warrant further research to find a cause or causes.

A large crossbreeding trial is being conducted in Canada using Norwegian Red sires on Canadian Holsteins, but it's too early to draw conclusions about calving ease or stillbirth incidence. Crossbreeding trials in California showed crossbred calves sired by Scandinavian Red sires from Holstein first-calving heifers had lower calving difficulties and a lower incidence of stillbirths. The crossbred heifers also had a lower incidence of calving difficulty at three per cent and stillbirths at 5.1 per cent than their Holstein counterparts with rates of 17.7 per cent for difficult calving and 14 per cent for stillbirths.

Canadian breeders will soon have proofs published for calf survival traits: Direct Calf Survival, a measure of the survival rate of a bull's offspring, male or female; and Maternal Calf Survival, a measure of the ability of a bull's daughters to have a live calf. Both maternal and direct traits contribute to whether you get a live calf on the ground, so pay attention to both. In the future, calf survival traits will also be included in some form in the Lifetime Profit Index to provide some overall selection to improve calf survival in Canada.

You may want to emphasize calving ease and calf survival information in sire selection for your first-calf heifers. You should also regularly report all stillbirths, whether male or female, to make Canadian genetic information as accurate as possible.

The knowledge gained from these studies, especially with first-calf heifers, can help you manage them at calving time to improve the chances of having a live calf. Discuss with your veterinarian the best strategy to minimize calving problems and calf losses, and maximize calf survival.

References:
Heringstad, B., Y. M. Chang, M. Svendsen and D. Gianola. 2007. Genetic Analysis of Calving Difficulty and Stillbirth in Norwegian Red Cows. J. Dairy Sci. 90:3500-3507.

Steinbock, L., A. Nashlm, B. Berglund, K. Johansson and J. Philipsson. 2003. Genetic Effects on Stillbirth and Calving Difficulty in Swedish Holsteins at First and Second Calving. J. Dairy Sci. 86:2228-2235.

Bicalho, R.C., K. N. Galvao, S. H. Cheong, R. O. Gilbert, L. D. Warnick and C. L. Guard. 2007. Effect of Stillbirths on Dam Survival and Reproduction Performance in Holstein Cows. J. Dairy Sci. 90:2797-2803.

This article first appeared in the Ruminations column of The Milk Producer Magazine, August, 2007.