Investigations into the critical aspects of the health and welfare of the bobby calves and dairy cows in Victorian dairy systems

© 2019 Monoar Sayeed PallabAnimal welfare is becoming critical to the general public, farmers and dairy industry. In Australian dairy farming systems, maintenance of good welfare of large numbers of surplus non-replacement young male dairy calves (bobby calves) that go for slaughter at an early age of 5 to 10 days old is essential. Another major area of concern for the sustainable dairy industry in Australia is the active control measures against infectious pathogens that may cause severe diseases and production loss such as enteric pathogens in neonatal calves and Mycoplasma bovis (M. bovis) infection in cattle. This thesis examines the health and welfare conditions of bobby calves after transportation for slaughter and the potential of bobby calf blood samples to detect herd level M. bovis infection in dairy cattle in Victoria, Australia. Blood samples from bobby calves were collected at a commercial abattoir in Victoria after transportation and lairage to assess their welfare by examining plasma biochemical profile. A quarter of the calves had a failure of passive transfer with a variation of passive immune status depending on which region they came from suggesting colostrum management practices are not similar in all the farms. Very few calves experienced severe hypoglycaemia and dehydration before slaughter. However, most of the calves had higher plasma creatine kinase and lactate indicative of muscular fatigue. It is not clear from this study whether increased creatine kinase was also due to the muscular bruising in calves. Distance or duration of journey and lairage time had no significant effect on energy metabolites, hydration state or muscular fatigue in bobby calves before slaughter. Most of the calves at the time of slaughter showed no evidence of substantial physiological compromise, and there was no significant association either between the transport distance and plasma analytes nor between the total duration of transport and lairage in relation with plasma analytes. These results highlight that bobby calves can be well managed from the property of origin to abattoir under existing management system in Victoria without unduly compromising their welfare. The enteric pathogen E. coli K99 was the most common pathogen (37.4%) followed by bovine rotavirus (8.1%), Salmonella spp. (5.1%) and bovine coronavirus (2.6%) in the faeces of bobby calves after their transportation. Infected calves with the higher acquisition of passive immunity had lower amounts of bovine rotavirus (BRV), bovine coronavirus (BCV) and Salmonella spp. in faeces. Hypoglycaemia was associated with increased amounts of shedding of E. coli K99 and BRV in the faeces of infected calves. Increased distance of transportation was associated with a higher excretion of BRV only. Breed and sex had no influence on pathogen prevalence in the faeces. This study highlights that the prevalence of major enteric pathogens in bobby calves is minimal except E. coli K99 compared to previously reported prevalence of enteric pathogens in Australian dairy calves with diarrhoea, and higher acquisition of passive immunity may play an important role in lowering pathogen load in faeces of infected calves. The potential for bobby calf blood samples to be used to detect maternal antibody against M. bovis for the estimation of herd-level M. bovis prevalence in dairy cattle in Victoria was also assessed. Antibodies were detected using antibody capture ELISA. Sera were evaluated for adequate transfer of passive immunity before screening for M. bovis specific maternal antibody. All the M. bovis positive samples were detected from the sera with adequate passive immunity which was consistent with M. bovis specific antibody being transferred from cows to bobby calves. A proportion of 33.3% and 32.9% positive herds against M. bovis were detected in the northern and south-eastern dairy region respectively. These results indicate that M. bovis is a common pathogen in the major dairy regions in Victoria. This study also suggests that the collection of blood from bobby calves at the abattoir is convenient and could be used as a source of samples for M. bovis prevalence and surveillance study in Victoria, Australia