Activities per year
Veal calves are mostly male calves and surplus female calves born on dairy farms. These animals may be considered by-products and they may not represent a priority for the dairy sector. As a consequence, these animals might receive poorer post-natal care on dairy farms (including feeding lower amounts of colostrum of moderate quality and poorer navel disinfection after birth). These calves undergo many challenges in the early stages of their life, such as transportation at a young age (14-20 d of age), commingling at a collection centre, and changes in housing and management conditions upon arrival at the veal farm. All these challenges contribute to the spread of pathogens and lead to a high susceptibility to diseases, and to high morbidity rates at the veal farms, especially with regard to respiratory and gastrointestinal problems. Consequently, at the veal farm, administration of antimicrobials is often high in the first weeks post-transport. However, a high use of antimicrobials is associated with antimicrobial resistance, which represents a threat to both animals and humans. To prevent high use of antimicrobials, alternative strategies, including the improvement of calves’ robustness before their arrival at the veal farm, might be used. Robustness can be defined as the capacity of an animal to cope with environmental challenges and to bounce back rapidly after challenges occur. Robust animals are well equipped to cope with endemic infections and to fight diseases and thus have a lower need for antimicrobials. Robustness can be measured in terms of physiological indicators, which reflect the capacity of an animal to regulate body functions in relation to external stimuli. This in turn might have an effect on morbidity, mortality rate of animals and antimicrobial use, which also represent additional measurements of robustness. Robustness can be shaped by early-life environmental factors and by animal functional reserves. The aim of this thesis was to investigate the role of different environmental and animal-related factors on robustness of veal calves. The most important environmental factors investigated in this thesis were 1) pre-transport diet (electrolytes vs. milk; fed at the collection centre), 2) transport duration (6 vs. 18 h) and 3) type of vehicle (conditioned vs. open truck). The results demonstrated that, in comparison to feeding electrolytes, feeding milk prior to transport contributed to a better energy balance and lower energy depletion and protein utilization. However, feeding milk also contributed to a higher prevalence in loose or liquid manure in the first 3 weeks post-transport compared to feeding electrolytes. Long transport duration (18 h) had more pronounced short-term detrimental effects compared to short transport duration (6 h). The combination of feeding electrolytes and long transport duration caused more profound body weight losses and greater short-term changes in blood variables of calves compared to feeding milk and a shorter transport duration. Effects of the type of vehicle were inconsistent and contradictory. Effects of pre-transport treatments on health status of calves were not present beyond week 5 post-transport. This result might be attributed to the high use of herd and individual treatments with antibiotics within the first period at the veal farm, which masked potential effects of transport-related factors on health status of calves. This thesis also showed that robustness of calves can also be affected by colostrum management at the dairy farm. Immune protection via maternal colostrum appeared to have a long term effect. In particular, the levels of immunoglobulins in calves’ serum (N-IgG) were negatively related to the likelihood of being individually treated with antibiotics and other medicines at the veal farm. Besides environmental factors, calf characteristics (such as transport age, breed and sex), characteristics of the dam (such as parity) may also be predisposing factors of robustness. This thesis showed that transportation of calves from the dairy farm to the veal farm at 28 d of age instead of 14 d led to a more advanced adaptive immunity in week 2 post-transport, a lower prevalence of calves individually treated with medicines other than antibiotics, a lower mortality rate and a higher carcass weight at slaughter. All these findings suggest that 28 d old calves are more robust than 14 d old calves.
|Doctor of Philosophy
|18 Jun 2021
|Place of Publication
|Published - 18 Jun 2021
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