Effects of age and state of incisor dentition on body composition and lamb production of sheep grazing hill pastures

Abstract

SUMMARYFifty-nine Scottish Blackface female sheep were used to measure the effects of age and state of permanent incisor dentition on the loss of body reserves during pregnancy and lactation and on the ability to replenish them during the dry period, while grazing hill pastures. There were 27 6½-year-old sheep (11 with sound mouths and 16 with broken mouths), 16 5½-year-old sheep (with all permanent incisors clipped to gum level) and 16 2½-year-old sheep. Samples of sheep from each group were slaughtered at the beginning of pregnancy and in mid-lactation, and samples of those with broken mouths and of 5½-year-old and 2½-year-old sheep at the end of the subsequent dry period. Carcasses were dissected into soft tissue and skeleton fractions and the changes in chemical composition of the former are presented. The sheep were weighed at approximately monthly intervals; lamb birth weights and growth rates to 6 weeks of age were recorded.There was no evidence that broken mouth or the clipping of the teeth impaired the ability of sheep to maintain body weight in early pregnancy, but there was evidence that sheep with broken mouths lost most weight in late pregnancy. There was also evidence that sheep with broken mouths may have poor milk yields as judged by the growth rates of their lambs but more data are needed to establish this conclusion.The young sheep were most able and the sheep with the broken mouths least able to resist catabolism of their soft tissue protein during pregnancy and lactation. The losses amounted to 18, 20, 21 and 30% in the 2½-year-old, 5½-year-old and 6½-year-old sheep with sound mouths and with broken mouths, respectively. The young sheep replaced their protein reserves more rapidly than the sheep with broken mouths. It is suggested that the ability to restore body protein may be related to maturity.There was evidence for a redistribution of protein in the body of undernourished sheep in mid-lactation. The soft tissues were overhydrated at this time but much of the fluid which accumulates during pregnancy had apparently cleared.