Growth, Development and Composition of the Ovine Conceptus and Mammary Gland During Pregnancy

Abstract

One-hundred and ten pregnant Targhee ewes that had been mated to Suffolk rams were killed at different stages of gestation. Mammary glands were removed and the gravid uterus was dissected into fetus, membranes, fluids and uterus components. The water, fat, ash, nitrogen and energy contents of the different components were determined. The uteri and mammary glands of 28 non-pregnant ewes were also analysed for chemical composition. Relationships were derived to describe growth and retention of the different nutrients in the various products of conception during pregnancy. Single and twin fetuses averaged 0.15 and 0.30 kg (total weight) at day 70 of gestation; and 6.21 and 10.64 kg at day 140, respectively. Growth rates of single fetuses averaged 31, 71, 129 and 199 g/d while those of twin fetuses averaged 47, 153, 236 and 202 g/d at days 80, 100, 120 and 140, respectively. Fetus(es) as a proportion of total conceptus weight increased from 14% at day 70 to 70% at day 140, while membranes and fluids decreased from 37 to 8% and 49 to 22%, respectively, over the same period. There were no significant differences due to number of fetuses carried. From day 70 to day 140 of pregnancy, fat content of the fetuses increased from 0.5 to 2.1%; fat-free organic matter increased from 7.3 to 13.2%; water decreased from 90.4 to 81.7%; ash increased from 1.9 to 3.0%; nitrogen increased from 1.0 to 2.0%; and energy increased from 0.45 to 0.93 kcal/g. As gestation progressed the mammary glands increased in weight, from approximately 0.5 kg at day 70 to 1.4 kg in single bearing ewes at day 140 and 2.0 kg in twin bearing ewes. Fat and energy contents decreased from 31.1 to 17.8% and 3.58 kcal/g to 2.63 kcal/g, while fat-free organic matter, water, ash and nitrogen all increased from 12.6 to 17.6%, 55.6 to 63.7%, 0.66 to 0.93% and 1.98 to 2.76%, respectively, over the same period. Mammary glands from multiparous ewes were higher in fat-free organic matter, ash and nitrogen than those from monotocous ewes. Total energy content at days 100, 120 and 140 of gestation was 0.835, 2.584 and 5.836 Mcal for single fetuses and 1.519, 4.968 and 9.599 Mcal for twin fetuses; while total protein content at the same stages of pregnancy was 107, 326 and 798 g for singles and 219, 668 and 1282 g for twins, respectively. The energy of the fetus(es) contributed 64.0, 79.7 and 88.6% of the total conceptus energy and 49.3, 69.6 and 80.0% of the total gravid uterine energy at days 100, 120 and 140 of pregnancy, respectively. The total protein of the fetus(es) made up 61.7, 77.7 and 87.1 % of the conceptus protein and 45.8, 66.3 and 77.7% of the gravid uterine protein at the same stages of gestation, respectively. Daily deposition of energy was 64, 131 and 220 kcal/d for singles and 136, 222, 221 kcal/d for twins, while protein retention was 7.6, 17.8 and 34.7 g/d for singles and 18.4, 28.4 and 33.0 g/d for twins at 100, 120 and 140 days post-mating.