Effects of age and state of incisor dentition on the chemical composition of the skeleton of sheep grazing hill pastures

Abstract

SUMMARYThe chemical composition of the skeleton, mandible and 4th lumbar vertebra of 59 Scottish Blackface female sheep from a ‘broken mouth’ farm was determined. There were 27 6½-year-old sheep (11 with sound mouths, 16 with broken mouths), 16 5½-year old sheep (with loose incisor teeth which at the outset of the experiment were clipped to gum level) and 16 2½-year-old sheep. Sheep from each group were slaughtered at the beginning of pregnancy and in mid-lactation and from those with broken mouths and from the 5½-year-old and 2½-year-old groups at the end of the subsequent dry period. The sheep grazed hill pastures and received an energy supplement during late pregnancy and early lactation.There were no differences between the 6½-year-old sheep with broken mouths and those with sound mouths in total skeletal mineral content or in the density of ash (ash: volume ratio) or organic matrix (organic matter: volume ratio) in the mandible and lumbar vertebra at the beginning of pregnancy or in mid-lactation. Nor were there differences in the density of ash or organic matrix between any groups, although the skeletons of the 6½-year-old sheep were larger. The lumbar vertebra, which is rich in cancellous bone, had a lower ash and organic matrix density in the 5½- and 2½-year-old sheep. It is suggested that bone mineralization may proceed slowly on such hill pastures.The rates of repletion of the skeleton during the dry period, 0·35, 0·47 and 0·66 g Ca/day, respectively, in the 6½-year-old sheep with broken mouths, 5½-year-old and 2½-year-old sheep were much slower than rates given in the literature for sheep under controlled conditions. It is suggested that factors other than the major nutrients, protein, Ca and P, may be limiting repletion of the skeleton.Recovery of the ash density of the vertebra was not complete at the end of the dry period. This was especially so in the sheep with broken mouths and resulted mainly from a failure to replace bone organic matrix.The implications for the development of broken mouth of cyclical changes in the density of cancellous bone and of evidence that the ability to maintain and to remineralize the skeleton deteriorates with increasing age, are discussed.