Factors governing the shape of the growth curve of body weight and the age at slaughter of Suffolk × Welsh lambs

Abstract

Curves of growth in live-weight, from birth to 16 weeks of age, of 362 Suffolk × Welsh lambs were analysed for the effect of sex, birth type, sire and test centre environment and related to variation in age at slaughter.The relative pre-natal disadvantages of twin lambs resulted in their curves of growth differing from those of single-born animals, particularly in males. Test centre environment exerted a marked effect in such cases. At one centre, male twins showed marked compensatory growth.Differences in growth existed between the 14 sire progeny groups. As the linear component of the growth curves decreased, the quadratic values became increasingly negative. Deceleration of growth was most marked in slowest growing progeny groups and this was accentuated by a poor test centre environment.These factors combined to influence age at slaughter, which was also related to birth weight of the lamb. Lambs at the best test centre reached slaughter weight 10 and 16 days earlier than lambs at the two remaining centres. Sires produced differences in age at slaughter of 10 to 14 days, within centres.