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Genetic selection impacts neonatal calf losses in Holsteins

John Mee Published on 29 October 2012
neonatal calf

Neonatal calf loss within 48 hours of calving is re-emerging as a major issue for producers.

Recent studies show an increase in calf losses, particularly in heifers, in dairy industries internationally. The problem is particularly important in Holsteins as they are the most widely used dairy breed globally.

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Neonatal calf loss rates internationally

There is wide variation in neonatal calf loss rates around the world. However, some countries stand out. Most concern centers on the high neonatal loss rates in heifer calves.

Calf loss rates in Holstein heifers in the U.S. (12 percent) and in Canada (10 percent) are high by international standards, even allowing for the differences in the definition of neonatal loss in the U.S. (0 to 48 hours) and in Canada (0 to 24 hours) and the voluntary nature of recording.

High neonatal loss rates are not however confined to the Holstein breed. In fact, the highest neonatal calf loss rate in dairy heifers in the world occurs in indigenous cattle in Iceland (23 percent), a country that has never imported Holsteins. Some of the lowest neonatal calf loss rates in heifers occur in Scandinavian breeds (e.g. Norwegian Red at 3 percent and Swedish Red at 3.6 percent).

Obviously there is also wide variation within breeds and between herds (0 to 30 percent has been recorded) within each country, so the effect of herd management can be far more important than the breed effect.

So why are loss rates high in Holsteins?

Unlike some of the other dairy breeds, Holsteins were genetically selected throughout the 20th Century to maximize milk production. Traditionally in many countries, there has not been emphasis on functional health traits such as calving ability and calf viability.

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In contrast, Scandinavian breeders have been selecting against poor calving ability and poor calf vitality in their dairy breeds for generations.

In addition, selection within a relatively small, effective genetic base has resulted in increased inbreeding rates in Holsteins, with resultant increased risk of neonatal calf mortality.

The result of these genetic influences is that both poor calving ability and calf vitality occur at a high rate in Holsteins. This difference was clearly shown when Holsteins were imported into Scandinavia where they had higher neonatal calf loss rates than the indigenous Scandinavian cattle.

What’s different about Holstein calves?

First, Holstein calves tend to be bigger than other dairy breed calves due to selection for greater stature in dairy type. Once Holstein calf birthweight goes above 45 kg (99.208 lbs), the risk of difficult calving increases significantly. This in turn increases the risk of neonatal mortality.

However, there is also evidence of increased calf mortality in Holsteins independent of calving difficulty. This suggests that some calves may be inherently less viable even where the calving is normal.

What can the dairy industry do about it?

To start, not all Holsteins are the same. There is wide variation within the breed between Holstein genotypes and between Holstein sires and dams in their calving ability and neonatal loss rates. This variation can be exploited in genetic selection programs.

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To do this requires national consensus on the genetic selection goals for each dairy industry. For some industries weighting more of the genetic selection index towards functional traits and less to milk volume may not be an economic priority, while in others it may be an imperative. And this may change over time as the relative economic value of production and non-production traits change.

In the near future it will be possible to identify genetic markers associated with high calf neonatal mortality not just in research studies, as at present, but at the general dairy industry level. This information will be used as a tool to aid in genomic selection of the sires of the future.

How can the producer prevent high calf losses?

While some farmers with Holsteins have high neonatal calf losses, there are many who do not, and then there are many who do not recognize such losses as abnormal – “bad becoming normal.” Recognition, recording and re-prioritization of the problem are key to prevention.

The basic principle of preventing neonatal losses is to analyze the decisions you make throughout the production cycle which can impact this variable.

For example, when you decide which semen to purchase, you can choose sires that will not result in more calving difficulty, particularly in heifers. The age and weight at which you mate your heifers will have an influence on their ability to calve down naturally.

Prior to or during pregnancy, the decisions you make about which vaccination and herd health measures you adopt can influence the viability of your neonatal calves.

In the last third of pregnancy, your management of the body condition and nutritional status of your heifers and cows has a critical bearing on the calving performance of the dam and of the viability of her fetus during calving.

Closer to full term, how often you observe for signs of impending calving and when you move pregnant cows to the maternity unit can both affect the chances of calving going smoothly or not. During calving whether you are present or not, how and when you intervene, what you do to revive a weak newborn calf and when you feed colostrum and dress the calf’s navel all affect your chances of successfully producing a healthy calf.

Finally, where calf death does occur, necropsy examination should form part of the SOP for controlling high calf losses. If you or your veterinarian don’t know why the calves are dying, it’s difficult to be specific about control measures.

Many of these decisions are made subconsciously without regard at the time to their potential future impact on neonatal calf mortality. Being conscious of this impact can be the difference between having problems and having productive herd replacements; it is improvement by the aggregation of marginal gains.

Summary

High neonatal calf loss rates are a re-emerging problem, particularly in Holstein heifers. Genetic selection policies of the past contributed to this problem. And genetic selection policies of today are part of the solution to the problem. At the farm level, the producer has considerable influence over many of the risk factors causing high neonatal calf loss once they recognize it as a problem and prioritize change. PD

Mee is the principal veterinary research scientist with Teagasc.

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