Repeated regrouping of pair-housed heifers around puberty affects their behavioural and HPA axis reactivities

Abstract

-This paper analyses the consequences of repeated regrouping of dairy heifers according to their behaviour, stress physiology and production. Thirty-two Holstein heifers were housed in pairs. Between 11 and 13 months of age, half were subjected to 16 pen relocations each time with a new peer (regrouped heifers), while the other half remained in the same pen with the same peer (controls). The heifers were observed in standardised behavioural tests comprising sudden (opening of an umbrella), novel (an unfamiliar arena) or predator-related (dog) stimuli. All behavioural tests were conducted on three sessions between the 13th and the 16th regroupings. The functioning of the HPA axis was assessed through blockade by dexamethasone and stimulation by ACTH after the 14th regrouping and stimulation by CRF after the 15th regrouping. Weight gain was assessed during the regrouping period and reproduction (No. of inseminations before successful insemination) thereafter. Regrouped heifers reacted less than the controls to the umbrella (χ 2 = 8.23, P < 0.05). They started eating more quickly in the arena (F = 10.8, P < 0.01). In the presence of the dog, they were less active (F = 6.26, P < 0.05) and tended to look at the dog less often (F = 3.63, P < 0.10). The reduction in behavioural responses from one session to the next one was more pronounced in regrouped heifers (e.g. number of eating bouts: F (session × treatment) = 4.23, P < 0.05). Regrouped heifers had lower cortisol responses to CRF. In conclusion, repeatedly regrouped heifers appear less disturbed by unusual situations and habituate to those more quickly. According to the behaviour of heifers and as suggested by their lower cortisol responses, diversity rather than stability of the social environment appears more beneficial to them. été élevées par paires. Au sein de huit paires, les animaux ont changé de partenaires une à deux fois par semaine entre 11 et 13 mois d'âge, pour un total de 16 mélanges (génisses " mélangées "). Ces mélanges s'accompagnaient également de changements de parc. Les huit autres paires sont restées inchangées (génisses " témoins "). La réactivité comportementale a été mesurée en exposant les génisses à un événement soudain (ouverture d'un parapluie), à un environnement nouveau (alimentation dans un nouvel enclos) et à un prédateur (chien). Chaque test était répété trois fois, entre le 13 e et le 16 e mélange. Le fonctionnement de l'axe corticotrope a été évalué à l'aide d'un test de freination par la dexamethasone puis stimulation par l'ACTH après le 14 e mélange et par un test de stimulation au CRF après le 15 e mélange. Le gain de poids a été évalué par pesée hebdomadaire au cours des 16 mélanges. Par la suite, le nombre d'inséminations avant insémination fécondante a été relevé. Les génisses mélangées ont réagi à l'ouverture du parapluie moins fortement que les témoins (χ 2 = 8,23, P < 0,05). Elles ont commencé à manger plus rapidement dans l'enclos nouveau (F = 10,8, P < 0,01). En présence du chien, elles ont été moins actives (...

Administration of dexamethasone per os in finishing bulls. II. Effects on blood parameters used as indicators of animal welfare

“…Activation of the hypothalamic-pituitary-adrenal (HPA) axis has been shown to weaken the immune system and this could have a significant impact on animal welfare through the hyperactivity of the adrenal cortex (Raussi et al, 2006). As a corticosteroid, dexamethasone affects the HPA axis (Rijnberk and Mol, 1997), and several studies conducted on cattle and veal calves have shown that such molecules might lead to leukocytosis, neutrophilia, eosinopenia, lymphopenia and monocytosis, as well as to an increase in the Neu/Lym ratio (Lan et al, 1995;Anderson et al, 1999;Thanasak et al, 2004).…”

Social stress as a cause of diseases in farm animals: Current knowledge and future directions

“…In dairy heifers, 202 agonistic behavior was less pronounced after seven repeated regroupings; yet still remained high 203 even after the sixteenth regrouping(Raussi et al, 2006). However, repeatedly mixing animals 204 during a critical time point may have some advantages.…”