AN OVERVIEW OF THE LATEST RESEARCH EXAMINING THE IMPACT OF STRESS ON THE HEALTH AND WELFARE OF BEEF CATTLE

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1 1 AN OVERVIEW OF THE LATEST RESEARCH EXAMINING THE IMPACT OF STRESS ON THE HEALTH AND WELFARE OF BEEF CATTLE Dr. Bernadette Earley, Animal and Bioscience Research Department, Animal & Grassland Research and Innovation Centre, Teagasc, Grange, Dunsany, Co. Meath, Ireland. The welfare status of an animal is dependent on its ability to cope and exist in harmony with its environment, such that good physical and psychological health is maintained. Improving animal welfare is an increasingly important aspect of livestock production systems due, to a large extent, to increased consumer concern about the source of animal products. Animal welfare has become an integrated part of quality assurance programs for sustainable animal production, considering that welfare, health, management, economy, consumer acceptance and environmental impact are depending on each other. In animals, stress occurs when an animal s homeostasis is disrupted, the stress response consists of a set of physiological mechanisms designed to return to homeostasis. The two distinct systems that link the initial perception of the stressor to this response are the sympathetic-adrenal-medullary (SAM) axis and the hypothalamic-pituitary-adrenal (HPA) axis. These two stress pathways, whose response functions are central to survival, are also central to the stress-immune axis activation that can lead to disease susceptibility. Activation of the HPA axis results in a significant release of the steroid hormone, cortisol, from the cortex of the adrenal glands. Systemic cortisol concentrations increase several minutes after perceived threat and can last for a number of hours and recur in waves if the threat (stressor) is not removed. Cortisol is a potent glucocorticoid that has multiple effects on organ systems involved in glucose homeostasis, blood pressure regulation, behaviour modification, inflammation, and immune function. The immunosuppressive effects of cortisol may serve as physiological down-regulators of initiated immune responses during recovery from infection or tissue damage. Bovine respiratory disease (BRD) or shipping fever and its associated severe lung inflammation continues to be the leading cause of death in young cattle and apparently results from ill-defined alterations in immune function induced by transportation stress and via increased exposure to pathogens as animals are commingled and moved to new locations. Weaning stress is one component of a series of stressors which is encountered by the beef calf during its lifetime and can be described as multifactorial combining physical, nutritional and psychological stress. In suckler herds, in Ireland, calves generally remain with the cows at pasture until they are weaned usually between 5 and 9 months old. In addition to removal from the cow, the weaning procedure may be compounded by other stressors occurring around the same time, e.g. change of diet (grass and milk to conserved feed with or without concentrates), change of

2 2 environment (outdoors to indoors), transport/marketing, and/or castration. Weaning therefore can be a multi-factorial stressor, in which, nutritional, social, physical, and psychological stress are combined. Psychological stress is present in the form of maternal separation and social disruption, whereas physical and nutritional stressors are often present through the introduction and adaptation to a novel diet and novel environment. More recently, we have reported that abrupt weaning is a stressful event for the beef calf and cow as evidenced by the altered physiological and immunological responses, namely increased neutrophil number and decreased lymphocyte number Our research at Teagasc has indicated, using conventional blood indicators of stress, that abrupt weaning (versus not weaning) alone is stressful to the suckler beef calf with alterations in immune function and hormonal mediators of stress still evident 7 days post-weaning. Weaning is a multifaceted stressor that usually involves numerous husbandry practices, including the abrupt separation of the beef calf from its dam, a nutritional adjustment to a non-milk diet, and social reorganisation and, additionally, is often associated with housing. The degree to which homeostasis becomes unbalanced and leads to disease during stress is influenced to a large part by the impact of stress on leukocytes of the immune system, namely the neutrophils. Neutrophils (also known as polymorphonuclear leukocytes or PMN s) are phagocytic granulocytes of the innate immune system that provide a crucial first-line defence against invading pathogens, especially in cattle. Housing has been reported to alter the neutrophil and lymphocyte immunophenotype of calves, along with the acute phase response, with a more pronounced stress response occurring in calves weaned at housing compared with those housed with their dams. Alterations in calf immunity following weaning stress are of great importance as these changes are thought to be associated with increased incidence and severity of respiratory disease. Neutrophilia is one of the most frequently reported biomarkers of stress in cattle following weaning and housing. Stress associated with weaning has been linked to immunosuppression and higher incidences of bovine respiratory disease (BRD), mortality and related costs in newly weaned cattle entering feedlots. The transport of livestock can have major implications for their welfare, and there is strong public interest and scientific endeavour aimed at ensuring that the welfare of transported animals is optimal. Physical factors such as noise or vibrations; psychological/emotional factors, such as unfamiliar environment or social regrouping; and climatic factors, such as temperature and humidity, are also involved in the transport process. Measurements of transportation stress encompass physiological, immunological and behavioural measurements. Circulating cortisol as an indicator of the HPA axis activation is clearly the most commonly utilised measurement, and increases have been observed in nearly all transportation studies of cattle as compared to pre-transportation concentrations or those obtained from

3 3 non-transported counterparts. Physiological and haematological responses associated with transport of animals are well studied; increased neutrophil and decreased lymphocyte numbers following transportation have been documented in previous studies. Furthermore, feed withdrawal can impact on animal welfare, through hunger and metabolic stress. Increases in plasma concentrations of metabolic markers such as lactate, beta-hydroxy-butyrate and urea have been used to measure the metabolic impacts of transport in cattle. The age of the cattle transported can have a great effect as instances of morbidity and mortality increase in transported calves younger than 3 weeks of age, which may be confounded by the stress incurred by simultaneous weaning. More recently, our group explored gene expression changes in blood neutrophils following truck transportation of young 12 month old Belgian Blue Friesian bulls (previously weaned at 10 days of age) for 9 hours on Irish roads and reported that transportation stress altered the expression of four neutrophil genes whose protein products are key in the regulation of inflammation related to clearance of bacterial infections. We reported transportation stress altered expression of four neutrophil genes whose protein products are key in the regulation of inflammation (Fas, L- selectin, and matrix metallopeptidase 9 (MMP-9) and clearance of gram negative bacterial infections (Bactericidal/Permeability-Increasing protein (BPI)), but left unchanged the expression of three genes (betaglycan, A1, GRα) known to be affected in other models of bovine stress. The gene expression profiles for the four affected genes suggested that transportation stress induced a state of heightened inflammatory and tissue sterilizing potential in circulating neutrophils. These expression changes largely correlated with the neutrophil count profile, which relates to blood cortisol concentration in numerous models of bovine stress. The observed gene expression changes for Fas, MMP-9, L-selectin, and BPI suggested that transportation stress induced a state of heightened inflammatory activity in circulating neutrophils. While the majority of cattle are fattened as young bulls in mainland Europe, male cattle are predominantly castrated and fattened as steers in Ireland. The necessity for the castration of male cattle intended for beef production varies with different countries, depending on the management and rearing systems employed by the producers, and the intended beef market supply. Castration is considered an essential husbandry management practice and is performed on calves because it reduces problems associated with aggressive and sexual behaviour of bulls. Castration is a husbandry procedure, which can cause pain and discomfort and if done incorrectly may result in subsequent health problems. Application of local anaesthesia prior to castration is mandated in some countries, and significantly reduces the cortisol response to castration. In Ireland, use of anaesthesia is required for surgical/burdizzo castration of cattle over six months of age. In contrast,

4 4 castration of calves without use of anaesthesia must be performed before they reach two months of age in the UK. Castration of male cattle has been shown to elicit physiological stress by increasing plasma cortisol concentrations, inflammatory reactions, pain associated behaviour, suppression of immune function and a reduction in performance. Burdizzo castration has been shown to be less stressful for bull calves of age of 5 to 6 months than surgical castration and when it is correctly applied the method causes the least stress and complications compared with surgical or rubber ring castration. Our research demonstrated that the routine practice of castration of calves without use of analgesia or anaesthesia should occur before 2 months of age in order to minimize the physiological stress (cortisol), inflammatory reactions (acute-phase proteins, scrotal swelling and surface skin temperature), and by inference the pain associated with burdizzo castration. The administration of lidocaine local anaesthesia (LA) for castration is a standard procedure employed by veterinary practitioners. However, our data has shown that LA is not effective in reducing the overall stress (cortisol) response associated with castration. Local anaesthetic causes increased scrotal swelling when used in conjunction with Burdizzo castration. We also reported that the degree of analgesia (as defined by the suppressive effect on integrated cortisol response) induced by the epidural anaesthesia was demonstrated to be no better than local anaesthetic for castration. The duration of anaesthesia following the regional infiltration of lignocaine without an added vasoconstrictive agent is approximately 1 h. We reported that Ketoprofen (K), a non-steroidal anti-inflammatory drug (NSAID), was superior to lidocaine local anaesthesia or combined local anaesthesia with ketopprofen in suppressing the overall plasma cortisol elevation associated with castration. Recent studies showed that banding or Burdizzo castration does not induce a general systemic inflammation and does not significantly affect peripheral leukocyte inflammatory cytokine gene expression in 5.5 month old calves. This latest study showed that systemic inflammatory markers are not altered by Burdizzo or banding castration in 5.5 month old calves compared with intact controls. The findings reported that Banding or Burdizzo castration did not have any major effect on peripheral leukocyte inflammatory cytokine gene expression; Banding castration caused a greater proinflammatory cytokine gene expression reaction than Burdizzo castration and carprofen administration can affect IL-6 gene expression levels in Burdizzo castrated animals. There is a general perception among producers that delaying castration could extend the production advantages of keeping animals as bulls beyond puberty or weaning. While after puberty, bulls always grow faster than castrates, the live-weight advantage is largely lost when the bulls are ultimately castrated. A number of studies

5 5 have shown no advantage in delaying castration up to 17 months of age in terms of slaughter weight or carcass weight at 22 months. Our group conducted an on-farm study which compared Burdizzo with banding as castration methods using 12 month old bulls. Animals weighing 399kg from four different farms were assigned, to one of three treatment groups: banding castration (Banding; 80 bulls), Burdizzo castration (Burdizzo; 83 bulls), or controls (control intact; 80 bulls). Local anaesthesia was given with injection of 2% lignocaine (local anaesthetic). Animals were injected 15 minutes prior to banding or Burdizzo castration. The band was applied using the Callicrate Smart Bander. Covexin-8 containing tetanus toxoid was administrated 4 weeks before (primary dose) and on the day of castration (booster). All animals were turned out to pasture on the day of castration. Both castrate groups lost in excess of 1.0kg/day in the first two weeks after castration. Intact bulls lost 0.49kg/day, this is typical for this type of animal going to grass. Overall intact bulls grew faster than castrates and performed better than either castration treatment. There was no difference between the performance of Band and Burdizzo castrates during the period 15 to 84 days post-castration. In recent years the scientific assessment of farm animal welfare has significantly advanced through the application of multidisciplinary scientific approaches (ethology, physiology and immunology). This allows the impact of husbandry management procedures to be assessed using evidence based biological indices of welfare. Tools developed in the past decade in the fields of functional genomics and proteomics have allowed for the identification of thousands of molecular changes at once in physiological or disease states. Use of these tools may discover potential targets for therapeutics and genetic selection and may present a pattern of genomic or proteomic changes as biomarkers of a disease. It has long been observed that an association exists between stress and disease susceptibility, namely BRD, in domestic farm animals, although a definitive causal factor still has yet to be defined. Many researchers have implicated a suppression of the host s immune system by stress that allows opportunistic infectious pathogens to invade.