Welfare assessment of Australian bobby calves using blood parameters

© 2021 Natalie Wallace RoadknightNon-replacement dairy calves in Australia, known as bobby calves, are typically fasted and transported to abattoirs for slaughter at around 5-10 days of age. Bobby calves are particularly vulnerable to poor welfare outcomes due to their low body fat reserves, immature immune systems, and their lack of herding behaviour, which makes them difficult to handle. The main aim of this research was to assess the welfare of bobby calves after transport, fasting, handling and lairage, and to identify risk factors for poor calf welfare. An additional aim was to evaluate the welfare of cows and calves in two prolonged cow-calf contact systems. Avoiding early separation of cows and calves has potential health, welfare, and social licence benefits. To start with, a method for collecting blood samples at exsanguination was validated for blood parameters relevant to calf welfare, including packed cell volume (PCV), plasma glucose, and serum total protein, beta-hydroxybutyrate (BHB) and urea. Haematology and biochemistry reference intervals for dairy calves aged 5-12 days old were then established. A method for estimating calf age using total protein, immunoglobulin G and gamma-glutamyl transferase was tested, but estimates of calf age were not reliable enough for further use. Next, blood samples were collected at exsanguination from 4484 bobby calves at three Australian abattoirs. Blood samples were analysed for indicators of energy status (glucose and BHB), hydration (urea, PCV, and total protein), muscle damage/fatigue (creatine kinase (CK)) and colostral immunity (total protein). Transport distance was estimated based on scanned ear tag data. Transport distance had clinically small, though statistically significant, effects on most blood parameters measured. With increasing transport distance, glucose was more likely to be low, and PCV and total protein high. Unexpectedly, CK was more likely to be low with longer transport distances. It was theorised that this could be due to loading being a high risk time for muscle damage. A number of bobby calves had blood measurements outside of the reference intervals. Twelve percent of calves had PCV values consistent with anaemia, 11% of calves had urea values consistent with dehydration, and 35% of calves had total protein values indicative of failure of passive transfer of immunity. These results show that a large proportion of calves were at risk of illness due to failure of passive transfer, while a smaller proportion of calves may have been compromised due to pathology or fasting. Two systems for managing cows and calves together on dairy farms were also compared. It was found that cows separated from their calves for half days were more restless in the dairy, and, when reunited with their calves, avoided nursing more and performed more agonistic interactions, compared with cows separated from calves for milking only. Half day separation may, therefore, have some negative welfare impacts on cows, compared to separation for milking only. However, further research is needed to compare the half day separation to early cow-calf separation, as there may be relative benefits to half day contact. The overall conclusions of this body of work were that transport distance had relatively minor effects on the blood parameters measured, but very long distances appeared to affect calves more per km travelled. Additionally, around a third of bobby calves had failure of passive transfer, which puts them at risk of infectious disease. Minimising transport distances and improving colostral immunity are thus areas where the risk of poor bobby calf welfare can be reduced in the current system. A smaller proportion of calves showed evidence of dehydration and anaemia, which could indicate sub-optimal health and welfare. Further research is warranted to investigate the aetiology of these conditions. Finally, the research presented here on two cow-calf contact systems provides evidence of a negative welfare impact on cows and calves separated for half days, compared with those separated for milking only. Some of these impacts could potentially be managed with the provision of milk to calves during the separation period, however this would require further research to confirm. The results of this study have helped to identify areas within the current system that can be targeted to improve bobby calf welfare. However, a whole system change, including the abandonment of both early life slaughter and early cow-calf separation, will likely be needed in order to align with public values and ensure the dairy industry has a social licence to operate