Veterinary Science Collected Works - Theses
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ItemWelfare implications of castration and disbudding procedures on calves( 2020)Castration and disbudding are necessary husbandry practices commonly performed in farms which have the potential to induce stress and pain if not managed correctly. Depending on the severity of a stressor, potential stress responses can suppress immune function, lower resistance to disease-causing factors, contribute to, and result in, reduced animal welfare. Scientific literature is discordant on what recommendations should be transferred to farmers and practitioners regarding the preferred age to castrate and disbud calves. This lack of scientific support to guide recommendations is even more noticeable in suckler beef calves, since most of the disbudding studies have used dairy calves and most of castration studies have used dairy calves or calves older than 6-mo-old. In this thesis, a series of studies were conducted to investigate: a) the age-related differences in plasma cortisol, acute phase protein, metabolite concentrations, haematological variables, behaviour and performance of suckler beef calves in response to Burdizzo castration; b) the effect of sex, breed and age on horn bud size of dairy and beef calves at disbudding; c) the relationship between age and horn bud size of dairy and beef calves at disbudding; d) the horn bud growth in Holstein Friesian calves. Results indicate that Burdizzo castration caused significant stress in 2.5- and 5.0-mo-old calves, characterized by the increase in plasma cortisol concentrations, scrotal swelling, and abnormal behaviours observed after treatment. These responses were reduced by castrating calves at younger age. A secondary stress response was observed, which was greater in older castrated calves, suggesting that calves castrated at older ages have a prolonged overall stress response, compared to younger calves. There was no effect of castration on haematology profiles, haptoglobin, metabolites, body temperature and growth performance. Thus, if calves are to be castrated without analgesia or anaesthesia, then it would be preferable to do this at 2.5-mo-old rather than later, such as 5.0-mo-old, in order to minimize the physiological stress, scrotal swelling and pain-related behaviours associated with Burdizzo castration. Horn bud size at time of disbudding, irrespective of calf sex, was greater in Holstein-Friesian calves than Charolais, Simmental and Limousin calves. These results suggest that horn bud develop differently in beef calves compared with dairy breed calves. In addition, the relationship between age and horn bud size was very weak in all breeds studied with no difference due to calf sex. This means that the age of the calf is not a good predictor of the horn bud size. Therefore, the age of the calves is not a good parameter to guide recommendations on the best age to disbud calves and use of pain relief due to the great variation in horn bud size within and between breeds. The findings of this thesis will have implications for the welfare of cattle in relation to best recommendations regarding the age at castration of suckler beef calves and disbudding of dairy and suckler beef calves.