Effects of a difficult calving on the subsequent health and welfare of the dairy cows and calves
Barrier, Alice Cécile Madeleine
Yearly calvings are essential to the sustainability of modern dairy farming. Currently, calving difficulty (or dystocia) affects one in six calvings among UK dairy herds but vary from 2 to 50% internationally. In dairy cows, despite reports of impaired performance, the extent and threshold of the effect of dystocia on health and performance remains unclear. Over the past years, there has also been increasing concerns about the levels of pain experienced by the dystocial cows. Better understanding of their parturition progress and behaviours is needed so that informed decisions on pain mitigation can be taken. Additionally, the impact of dystocia (besides stillbirth) should also be addressed in dairy calves. The objective of this study was to address the effects of a difficult calving on the health and welfare of both dairy cows and calves. Retrospective analyses of an experimental farm’s detailed records were used to relate calving difficulty with health and performance of the dairy cow. The results showed that after any difficulty at calving, dairy producers incur long-lasting shortfalls in milk sales. Dystocial cows also have impaired fertility, are more likely to leave the herd early and have a higher risk of dystocia at the following calving, thus there is a long-term detrimental impact on dystocial cows. Video monitoring of calvings allowed detailed investigation of the parturition progress and behaviours of dystocial Holstein cows giving birth to singleton liveborn calves. The study of calving behaviours and parturition progress indicated longer later stages of parturition, increased restlessness and tail raising in the six hours preceding expulsion of the calf, for dystocial cows receiving farm assistance compared with cows calving unaided. This may relate to the expression of higher levels of pain when dystocia occurs. The onset of maternal behaviour was not delayed following calving difficulty, and firm conclusions could not be drawn from investigation of some behavioural indicators of pain in the first three hours postpartum. Experimental work allowed the monitoring of a cohort of 496 calves born with various degrees of birth difficulty over two years. All but one vet assisted calves were born dead, and farmer assisted calves were more likely to be stillborn than calves born without assistance. Stillborn dystocial calves displayed larger internal damage, than stillborn eutocial calves, but they did not have a different body shape at birth than dystocial calves that survived. Dystocial dairy calves that survived the birth process had lower vigour at birth, had higher salivary cortisol, acquired lower passive immunity and received more health treatments in the neonatal period. Dystocial heifers also had higher mortality rates by weaning but had similar growth to first service. Historical records from the farm also showed that dystocial heifer calves were three times more likely to have died by weaning and by first service than calves born without assistance. For those who survived, there was, however, no indication of altered growth to weaning or subsequent impaired fertility. This may be explained by the early mortality of the most badly affected calves or by farm management. However, their high mortality rates still raise welfare concerns. Altogether, results suggest that dairy calves born with any difficulty have poorer welfare in the neonatal period and possibly beyond. The experience of any calving difficulty in dairy cattle therefore not only impairs the welfare of the cow, but also the welfare from their resulting calf. Any strategy implemented to lower the occurrence and mitigate the effects of dystocia will therefore improve the welfare of the cows, their calves and enhance the farm’s economic sustainability.