Components of weight loss in pregnant hill ewes during winter

Abstract

Live weight of 180 free-grazing Blackface ewes was measured approxim-ately every two weeks throughout a 12-month period. Mean live weight was at a maximum (47 kg) in late autumn prior to mating and declined progressively to 39 kg at about the time of parturition.Six ewes were slaughtered in November before mating, six at about the 16th week of pregnancy, and a further 11 in April during the final week of pregnancy. The loss of weight of maternal tissues (i.e. live weight less the weight of fleece and contents of the gastrointestinal tract and gravid uterus) during this period was more than 20% (7·5 kg) and comprised 51% of the fat, 14% of the water, and 20% of the protein plus ash present at maximum live weight. During the earlier stages of pregnancy there was an appreciable loss of water from the maternal tissues, but in late pregnancy the rate of water loss decreased and that of fat increased considerably.The distribution of fat throughout the maternal tissues at different levels of total fat content and the pattern of fat mobilization from various depots are described. The largest single contribution to fat loss during the pregnancy period was that of the subcutaneous reserves, which were depleted by 86%, most of this being lost during the first four months. At the other end of the scale bone fat reserves were reduced by only 25%, almost all of this occurring during the final month.