The effects of different intakes of crude protein on nitrogen utilization in the pregnant and lactating rabbit

Abstract

ABSTRACTThree experimental diets (L, M and H) containing 135, 175 and 210 g crude protein per kg dry matter respectively were given to crossbred does in two experiments. Protein quality was constant throughout.In experiment 1 a total of 18 does (six per diet) were given the diets during two successive reproductive cycles. Losses of nitrogen in faeces and urine were estimated for four successive 7-day periods in each 28-day lactation period. Litters were culled at birth to give ‘high’ and ‘low’ lactational loads with 8 and 4 pups respectively. Total 28-day milk yields on diets L, M and H were 3·89, 4·82 and 5·27 kg respectively with eight pups sucking, and 302, 400 and 400kg respectively with four pups. These differences in milk yield were directly reflected in the weights of the pups when weaned at 28 days of age. There was no effect of diet on milk composition, pup birth weight or litter size. Does given diet L did not always consume their allotted ration and this may have affected the results.The proportion of digested nitrogen utilized for milk protein synthesis differed significantly between diets and lactational loads, and was at its maximum (0·72) when diet L was given to does with eight pups. Does suckling eight pups retained 005 of the nitrogen they digested in their body tissues and those with four pups 0·13; there were no differences between diets in this respect.In experiment 2 the nitrogen retention of 18 does (six per diet) was measured during pregnancy. Nitrogen retention increased as pregnancy progressed, and overall 0·20 of digested nitrogen was retained for conceptus growth and doe body tissue accretion.