STUDIES ON THE GROWTH, GAIN AND CARCASS V ALUE OF PRIMIPARA DURING SINGLETON AND TWIN PREGNANCIES .2. GAIN OF BODY SUBSTANCES AND ENERGY, BIRTH WEIGHTS AND COURSES OF CALVING

To ascertain the gain in matter and energy, 38 animals were slaughtere d after different intervals and subjected to whole body analysis. The dry weight and fat content increased during the first half of the preg nancy and remained almost constant during the second. The protein and ash content remained relatively constant throughout the study. The pro portion of fat decreased in all four groups after calving. In the prod ucts of conception, the amounts of all categories of matter Increased during the experiment. Singleton calves had a significantly higher fat and energy content than twin calves at the time of birth. The weight of the twins was 78.9 % of the weight of the singletons. The nutrition al level had a positive effect on the weight of twins at birth. Howeve r, the normal birth rate decreased as the nutritional level increased. During the last four months of pregnancy, increases in nutritional le vel correlate to an increase in daily gain in dry matter, protein, fat and ash. The energy gain varied between 6.9 and 7.5 MJ ME/d during th e first half of pregnancy and between 3.7 and 4.7 MJ/d during the seco nd. The calculated energy requirement for heifers during twin pregnanc y is 11 % higher than during singleton pregnancy. A safety margin of 1 0 % should be added during the last two months of pregnancy to avoid p repartal energy deficits.