Haptoglobin, cortisol, A/G ratio and IGF-1 in goat kids around weaning

Weaning is the most stressful event in the life of young ruminants. Since stress can affect endocrine and immune functions, weaning often results in a period of growth stasis and risk of disease. In light of this, the aim of this study was to evaluate the effect of weaning on growth and on some physiological mediators of stress and immune function. Eleven Saanen goat kids were studied from day 3 to day 50 of age. Kids were randomly divided into two groups: MILK (6 animals) and WMIX (5 animals). All were fed goat milk to age 29 days. After that, MILK kids continued to receive milk, while WMIX group underwent weaning, in which milk was gradually replaced by solid feed. WMIX kids were completely weaned on day 48. During the experimental period, dry matter intake (DMI) and body weights (BW) were recorded and blood was analyzed for metabolic traits, for indicators of health status (cortisol, haptoglobin and albumin/ globulin - A/G ratio) and for IGF-1, which has a crucial role in postnatal development. Starting from day 37 of age, DMI began to lower in WMIX group. On day 50, glucose, amino acids and urea were significantly lower in WMIX kids. On the same day, plasma IGF-1 was also lower in WMIX kids, as possible consequence of the lower plasma glucose and amino acids. Despite these differences, BW did not differ between groups, throughout the entire period. Along the experimental period, plasma cortisol was always low in both groups, signaling no stressful condition, even if from day 44 to 50 of age, cortisol level significantly increased in MILK kids. This last result may indicate a function for cortisol as metabolic hormone involved in glucose homeostasis, rather than as telltale sign of poor health. In fact, no difference was observed neither in plasma haptoglobin, nor in A/G ratio, which are useful tools for suggesting when the animal is pathologically or physically challenged. Results imply that a gradual transition from milk to solid feed does not affect the health status of goat kids, but it can decrease plasma cortisol, as hormone involved in glucose metabolism