EFFECT OF DIETARY-PROTEIN LEVEL AND YEAST CULTURE ON GROWTH, BLOOD PROLACTIN AND MOHAIR FIBER CHARACTERISTICS OF BRITISH ANGORA-GOATS

Twenty-four male castrate British Angora goats aged about 10 months and weighing 18.5 kg live weight initially were studied in an 84-day experiment. They were allocated in a 2 x 2 factorial design to receive diets containing, kg-1 dry matter (DM), concentrations of crude protein (N X 6.25) of 110 g low protein (LP) or 180 g high protein (HP) per kilogram and supplemented (Y) or not (O) with 2 g per head per day of the yeast culture product 'Yea-Sacc'. The animals were offered the diets at approximately 0.95 x the weight of voluntary food intake. In comparison with the LP diets, the HP diets on average increased liveweight gain, raw mohair fibre yield, fibre diameter measured on a 100 cm 2 midside sample, improved food conversion efficiency, and variably increased concentrations of glucose, urea and prolactin in blood. There was evidence of significant increases in liveweight gain attributable to the yeast culture supplement during the early part of the study on Diet HP only, and variable reductions in the yield of raw fibre, but the blood characteristics measured were not affected. Attention is directed particularly towards the positive association of elevated dietary protein, fibre yields and plasma prolactin concentrations in the context of the biological control of fibre growth.