Coping strategies in dairy cows

The central aim of this thesis is to investigate whether individual dairy cows display different and coherent patterns of physiological and behavioural stress responses. Such responses enable them to successful adapt in a changing environment.In Chapter 1, current concepts of adaptation and stress are introduced. Adaptation is necessary when the individual's need to perform specific behaviour, does not match the current or anticipated perceptions of the internal or external environment. Such a condition is termed stress . Physical and/or psychological factors that cause, support or magnify such a mismatch are called stressors . The behavioural and physiological responses that compensate this discrepancy are termed stress responses . Adaptation can be measured as the fade out of these responses.The degree, in which adaptation is accompanied by stress, is primarily determined by uncertainty, perceived by the organism, when it is not clear how and if adaptive changes can be realized. Individuals may differ remarkably in the way they cope with this problem. In such a situation, broadly speaking, their behaviour ranges between actively avoiding or tackling the problem and passively undergoing it. These two behavioural patterns strongly resemble the classical stress responses, ie fight/flight versus conservation/withdrawal, and are characterized in rodents and man by a specific, integrated pattern of cognitive, emotional, behavioural and physiological responses, termed coping strategies or coping styles .The active coping style is characterized by active behavioural responses as well as by dominating sympathetic activity. Increased concentrations of primarily noradrenaline and to a lesser extent adrenalin and glucocorticoid accompany active coping responses. Behavioural inhibition and activation of both the adrenomedullary and the hypothalamus-pituitary-adrenocortical systems is typical of the passive coping style. Passive coping is associated with increased concentration of adrenalin and corticosteroids and to a lesser degree also of noradrenaline.Increase in heart rate is suitable for measuring dominating sympathetic activity. Plasma concentrations of cortisol are used for estimating adrenocortical activity. To reliably measure these two parameters in dairy cows, methods were developed for both the recording of heart rate and the 'stress-free' collection of blood samples.For heart rate measurements in dairy cows, the Polar® Sport Tester has been modified and validated (Chapter 2). Simultaneous heart rate recordings with both the Polar® and classical ECG-equipment indicated significant correlations between the measurements when cows were quietly standing (0.88) or walking on a treadmill (0.72). Artefacts, caused by muscle contraction, could be easily recognized by their characteristic heart rate patterns. Accordingly, missing values instead of erroneous measurements were produced.A method for collecting only a few blood samples from many cows is reported in Chapter 3. Evidence is produced that baseline cortisol concentrations can be measured in single blood samples that are collected by jugular puncture within 1 min of first approaching the cow. To prevent handling from confounding cortisol concentrations, it is necessary that cows are accustomed to handling and to being restrained. When blood samples need to be collected repeatedly, however, jugular puncture may induce an increase in cortisol concentrations which seems to depend on the handling experience of the animal and on individual differences.The separation of cow and calf, 2-3 days after calving, evoked only a slight increase in heart rate in cows during the first minute after separation (Chapter 4). During the first 10 min after separation, no other behavioural (activity, vocalisations) or physiological (heart rate, cortisol) signs of stress could be detected. This indicated that the removal of the calf after bonding could not be used for triggering an acute stress response in dairy cows in further experiments.In Chapter 5, the preference of dairy cows for visiting a particular side of the milking parlour has been studied in the light of evidence in mice that active coping animals easily develop behavioural routines. Marked differences were found between individual cows in consistency of parlour side choice. Some cows systematically visited one side of the parlour for a longer time, whereas others alternated randomly. Social factors hardly influenced this individual trait. It was surprising, however, that in cows which consistently visited one side of the parlour, deprivation of choice hardly elicited any stress responses (behaviour, heart rate, milk production). Side preference of dairy cows in the milking parlour thus seemed to be a consistent behavioural routine with only unimportant implications for the welfare of cows if it were to be interrupted.In Chapter 6, the short- and long-term consistency of behavioural and physiological responses of dairy cows, which were repeatedly tested in a 'novel environment' test, is described. Individual cows showed consistent and individual-specific stress responses. Consistency appeared in behaviour, in heart rate and in plasma cortisol concentrations within one week. Consistency of individual responses was also found for heart rate and plasma cortisol concentrations when tests were spaced 1 yr apart. Handling prior to the exposure to the novel arena, besides the exposure itself appeared to be an important stress-inducing element in the novel environment test. The study produced clear evidence that individual dairy cows differ consistently in the degree to which they respond to environmental challenge, ie a combination of novelty, isolation and handling. The treatment offers exciting opportunities for the objective assessment of an underlying characteristic or psychobiological profile, perhaps fearfulness.Ten cows with low and eight cows with high plasma cortisol concentrations in response to the short stay in novel environment, were selected out of the group of 58 heifers. Low- and high responders were labelled LC- and HC-cows respectively. After one year, while in second parity, these cows were separated from herd-mates one after another and isolated and tethered for 55 hr in a stanchion barn (Chapter 7). Intra-mammary administration of E. coli endotoxin produced an acute and transient mastitic episode in all cows with only mild mastitic and systemic reactions. As far as their response to endotoxin is concerned, HC- and LC-cows responded similarly. In response to isolation, however, HC-cows showed stronger stress responses than LC-cows, as indicated by a higher increase in rectal temperature, in cortisol concentration after injection of endotoxin and in the number of vocalisations. Between 8 and 10 h post injection (PI) the number of circulating lymphocytes in HC- but not in LC-cows decreased markedly (40%) to 1.58 x 10 6cells.ml -1and remained so until 21 h PI. These results show that the stress response of dairy cows during social isolation is associated with the number of peripheral blood leukocytes after intra-mammary administration of endotoxin. Because plasma cortisol concentrations hardly differed between HC- and LC-cows, noncorticosteroid factors are likely to be involved.In chapter 8, current theories about the control of animal behaviour and the generation of emotional responses will be briefly introduced. These two topics, together with the current concept of adaptation and stress, provide a basis for discussing the findings of this study in an integrated way. The question is addressed why the dichotomy between active and passive coping animals, as reported in rats and mice, is likely to be different in dairy cows. Cumulative effects of domestication, intensive rearing and handling, one-sided selection for milk production and a feminine brain may have weakened the stress response of dairy cows. Therefore, distinct coping styles may be distinguished, although it is likely that such forces have shifted the coping behaviour of dairy cows to a more passive style. Finally the question is addressed how results from this study could contribute to the development of future management practices and breeding strategies.