The effects of thyroxine and climatic factors on colostral gammaglobulin absorption in newborn calves.

Observations of 68 Friesian and Holstein X Friesian calves in a single herd with low neonatal mortality gave the following results: --The calves which will suffer from diarrhoea but survive were in a hyperthyroid state (high levels of hormonal iodine, T3 and free thyroxine index) compared with the healthy animals. --The concentration of plasma globulins, after colostrum intake was lower in diarrhoeic subjects calves than in the healthy ones. --For the whole group of animals, plasma hormonal iodine, at birth, was negatively correlated with the concentration of plasma globulins at 48 hours (r = 0,37, P less than 0,05). Thus, by reducing the absorption capacity of colostral globulins, an excess of thyroid hormones at birth could increase young calves sensitivity to various infections. To test this hypothesis, 12 Holstein X Friesian calves, born in the same stable and then transferred to outside individual boxes, were used. Six animals received thyroxine injections at birth and after 24 hours. All the calves received colostrum in the same conditions. The following results were obtained. --All the treated calves became ill (1/6 of the controls), independantly of their plasma IgG1 concentrations. --The capacity of calves to acquire colostral IgG1 varies considerably between individuals (maximum IgG1 concentrations and, probably, duration of intestinal absorption of IgG1). --The T4 injections at birth do not noticeably after IgG1 absorption. --Thyroxinemia at birth, reflecting the foetal concentration, is negatively correlated (r = 0,74, P less than 0.01) with the period of IgG1 absorption. --The outside temperature at birth is negatively correlated with the maximum IgG1 concentration (r = 0.78, P less than 0.01). These results indicate that a hyperthyroid state at birth, and, probably, during foetal development compromise the calves health: --by direct or indirect action, the intermediates of which are not known, --by reducing the period of intestinal absorption of immunoglobulins in addition. Moreover climatic factors such as ambient temperature at birth may influence acquisition of passive immunity.