ADJUSTMENT FACTORS FOR BIRTH-WEIGHT AND 30-DAY, 60-DAY, AND 90-DAY WEANING WEIGHT IN SHEEP

Multiplicative and additive adjustment factors for birth weight and 30 -, 60-, and 90-day weaning weights were calculated for two sheep breed types, by using field-record data collected by the National Sheep Imp rovement Program (NSIP). Factors were estimated for sex, type of birth and rearing (B/R), and ape of dam. The large breed types included the Columbia, Hampshire and Suffolk breeds, and the small breed types inc luded the Dorset, Polypay, and Rambouillet. The data consisted of 13 5 01 birth records, 3 423 30-day records, 10 988 60-day records, and 3 2 85 90-day records. The analyses included effects of breed, contemporar y group, sex, type of B/R, and age of dam. Subclass means and variance s were proportional for sex and B/R within breed type for most analyse s (p < 0.01), with increased weight associated with increased variatio n. Consequently, multiplicative adjustment for sex and type of B/R for these factors were recommended for birth weight and all weaning weigh ts. The subclass variances for age of dam were not heterogeneous withi n breed type (p > 0.25); consequently, additive adjustment for this fa ctor is recommended for birth weight and all weaning weights. Interact ions between sex, type of B/R, and age of dam were varied in significa nce, were inconsistent across analyses from various birth and weaning weights, and accounted for less than 2 % of the explainable variation in most analyses within breed type.