Studies on the metabolism of the ruminant by indirect calorimetry. II. The influence of pregnancy on the energy exchange of the goat

Abstract

The total metabolism of the pregnant goat remains at a steady rate from the 4th to the end of the 13th week of pregnancy. It increases steadily from the 14th to the 21st week, when a value is attained about 50 per cent, above the rate at the 14th week. Just before delivery the rate drops slightly. The increased metabolism is due partly to the increase in the mass of active protoplasm and partly to the stimulus exerted by the growing ovum on the maternal tissues. This stimulus tends to fall off slightly in intensity in early pregnancy and increases markedly in late pregnancy.Post partum the total metabolism drops suddenly and continues to fall until the end of the 5th week; but the metabolism per unit of weight increases steadily until the 4th week and then declines. This increased activity of the maternal protoplasm is due to the processes of involution and repair.In early pregnancy the increasing intra-abdominal pressure cuts short fermentation of food and causes the R.Q. to be higher in the pregnant than in the non-pregnant animal. As the pressure increases it begins to impede slightly the evacuation of the rumen so that the food ferments more thoroughly and the R.Q. falls slightly. After parturition the low intra-abdominal pressure aggravated by the laxity of the abdominal walls allows the food to remain longer in the rumen so that fermentation is more thorough and the R.Q. lower than in late pregnancy.