Behavioral and physiological measures in dairy goats with and without small ruminant lentivirus infection

Abstract

Although goats exhibit no visible symptoms of discomfort in the subclinical stage of small ruminant lentivirus (SRLV) infection, we examined their welfare at the behavioral and physiological level. Twelve SRLV-seropositive (SRLV) and eight SRLV-seronegative (control) goats in their first, second, and more than second lactation were observed for pain behaviors, locomotor activity, standing, lying, eating, rumination, social interactions, and comfort behaviors. Heart rate was recorded during resting and morning and afternoon milking. Concentrations of serum amyloid A and haptoglobin in blood serum, as well as milk yield and the following milk parameters were assessed: somatic cell count, fat, casein, total protein, lactose, total solids, solids nonfat, urea, citric acid content, freezing point depression (FPD), free fatty acids, density, and titratable acidity. Age but not infection status affected the time budget of the goats. The oldest animals were the most active and spent the most time on comfort behaviors. In general, the goats spent more time on neutral interactions and on standing still in the morning than in the afternoon. The average heart rate (HR) from all recordings was higher in control than in SRLV goats, but did not differ between goats of different ages. HR was lower in the morning than in resting and afternoon recordings. HR variability (root mean square of successive interbeat interval differences [RMSSD]) was higher at low temperatures. The strong correlation between cardiac response and temperature was particularly evident in SRLV goats (HR and temperature: r = 0.54, P < 0.01, RMSSD and temperature: r = −0.39, P = 0.01). However, RMSSD and acute phase proteins (serum amyloid A and haptoglobin) were affected neither by infection nor age of the animal. Milk yield and its composition did not differ between SRLV-infected and control goats, except for FPD, which was higher in controls. The lower FPD value of milk from SRLV goats than control goats may indicate a deterioration of metabolic processes in the infected mammary gland. As the goats presented no abnormal behaviors and the concentrations of the acute phase proteins were not elevated, the welfare of the infected animals was confirmed. The higher susceptibility to high temperatures should be considered in managing SRLV goats, and longer observation sessions are highly recommended to monitor any pain reactions.