On the relative growth and development of various breeds and crosses of sheep

Abstract

Records of the live and carcase weights of sheep exhibited at the Smithfield Show from 1893 to 1913 have been treated statistically. The results show the average weights, rates of growth, and proportions of the carcase in the different breeds of sheep at 9 months and at 21 months of age (see Tables II and V).On the average of all breeds the rate of growth declines from 4·7 lbs. per week from birth to 9 months of age to 1·7 lbs. per week from 9 to 21 months of age.The carcase percentage increases with age on the average from 61 per cent, at 9 months to 65 per cent, at 21 months and with it the percentage of fat from 5·7 per cent, at 9 months to 64 per cent, at 21 months. On the other hand the proportions of pluck, skin and alimentary canal (“Unaccounted for”) decrease with age.Ratios of early maturity are given for the various breeds and the factors which affect it are discussed.The average weights, rates of growth and proportions of the carcase are given for the different crosses of sheep (see Tables IX and XIII).From a comparison of crossbreds with pure breeds it would appear that crossing leads to increase in live weight and probably more early maturity. There is an indication that the proportions of carcase, fat and pluck are less but the proportions of skin and alimentary canal are greater in crossbreds than in the pure breeds of sheep.There is greater variation in live weight in the Cheviot and Blackface breeds than in the Leicester, Southdown, Hampshire and Suffolk breeds; in the latter breeds variability decreases but in the former breeds it increases with age.Variability in live weight at 9 months old has steadily increased from 1893 to 1913 but at 21 months old there has been little change.Some parts are more variable in their proportion to live weight than are others. Fat and alimentary canal are most variable, skin and pluck slightly less variable, while the proportion of carcase is less variable even than live weight.The variability of the proportions of carcase, pluck and alimentary canal increase while the variability of the proportions of fat and skin decrease with age.Within a breed and among animals of the same age the heaviest sheep generally have the highest carcase and fat percentage and the lowest percentage of pluck, skin and alimentary canal.A high proportion of carcase is correlated with a high proportion of fat and a low proportion of skin and alimentary canal at 9 months old. At 21 months old the same holds true with the exception that the sheep with the highest carcase percentage have not the most fat.The proportion of pluck does not appear to be correlated with any other part of the body except inversely with the live weight.During the period 1893–1913, although individual breeds show differences, the majority have increased in live weight at 9 months old but at 21 months old have remained practically constant in weight.The sheep exhibited in 1840 were very much fatter than those shown in the Carcase Classes of to-day and are probably comparable with those of the present-day Live Classes. Since 1840 Leicesters have shown a great increase and Southdowns a small increase in weight.The carcase percentage of sheep both at 9 and 21 months of age has steadily decreased during the period 1893–1913; this has been attended by an increase in the proportion of pluck, skin and alimentary canal.There is an indication that the influences which affect sheep in their first year of life (store period) affect their ultimate size.The seasonal variation in the weight attained by sheep is dependent on the rainfall; a high rainfall through increased root and fodder crops causing increased live weight.