Easier calvings deliver better replacements

Published 27 August 13

The issues associated with dystocia most commonly focus on the impact on the cow – including increased likelihood of experiencing difficult calvings at subsequent calvings, retained placenta, issues conceiving, etc...  But new research reveals just how seriously the viability and long term potential of the calf can be impacted as well, says to DairyCo’s Dr Jenny Gibbons.

The study, carried out by SAC in Scotland, found that up to a third of 490 calves born between 2008 and 2010 were born after dystocia. The heifer calves were followed from birth to first service and the bull calves from birth until they were sold or culled, usually between 11 and 22 days of age. Dystocia was measured as 1) no assistance, 2) farmer assistance of normally presented calf, 3) farmer assistance of malpresented calf and 4) veterinary assistance. 

A total of 7% (20 heifers and 15 bull calves) were born dead.  From the remaining 455 calves born alive, 79% were unassisted, 18% were farmer-assisted with normal presentation, and 3% were farmer-assisted with malpresentation. None required veterinary intervention.

Mortality rates were highest in the farmer-assisted malpresented calves with a total of 40% dying before weaning compared with only 9.4% of the farmer-assisted normally presented calves and 4.9% of the unassisted calves.

Overall, 2.8 times more farmer-assisted (normal and malpresented) heifer calves died before weaning than unassisted heifer calves. Previous studies in the US have also demonstrated higher death rates in dystocial-born calves up to a month of age and even up to first calving.

Dystocial calves alive at birth had higher physiological stress as demonstrated by higher salivary concentration levels within the first 24 hours of birth.  Farmer-assisted malpresented calves had higher rectal temperatures over the course of the first four days when compared with unassisted calves.  While this was only by 0.1°C, it’s possible that if challenged with colder environments, these calves may not be able to regulate their body temperature as well as unassisted calves.

The study also looked at absorption of colostrum immunoglobulins and found that more than 43% of dystocial calves were diagnosed with failure of passive transfer compared with around 27% of unassisted calves – possibly down to lack of oxygen and respiratory acidosis, which can happen after dystocia.   This was found through using the Zinc Sulphate Turbidity Test (ZST) to determine plasma immunoglobulin concentrations in blood samples taken from calves between 3 and 7 days of age.  Calves failing to have adequate passive transfer had ZSTs of 19g/l or less, indicating inadequate absorption of colostrum antibodies that help ensure optimal calf health and survival.

Overall, dystocial calves also required more non-routine health treatments and were treated for more days than unassisted calves.

So it’s clear that a difficult birth has potential long-term effects, reducing survival to adulthood and subsequent milk production. Calves born after dystocia can suffer from lack of oxygen (hypoxia), impaired breathing and internal injuries. Reduced passive immune transfer has been shown, even when allowed to suckle or given assistance with colostrum feeding. Dystocia also increases the likelihood of calf respiratory and digestive disorders.

As well as negatively affecting the welfare of live born dairy calves, dystocia increases the rearing costs of such calves – particularly through higher death rates and disease incidence. So this means that reducing dystocia can benefit both productivity and welfare, with potential preventative measures including improved nutrition of the cow, better calving environment, increased genetic selection for calving ease and optimised heifer rearing.  Improving calf care during and immediately after birth may also reduce the number of calves that die not just during the first hours, but also in the subsequent days and months of life.

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