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Abstract
Data from 5,585 straightbred Romney and Border Leicester × Romney lambs and 1,140 ewe hoggets over the period 1959 to 1967 have been used to study the effects of “breed” of flock, age-of-dam, sex, birth-rearing rank, and year-to-year variation on lamb and hogget fleece weights and live weights. The sheep were from six groups: a Romney control (RCR) flock, a Romney flock in which ewes were mated either to Romney (RER) or to Border Leicester rams (REB), and flocks of first-cross (F1), second-cross (F2 ) , and third-cross (F3) Border Leicester X Romney ewes mated to first-cross Border Leicester × Romney rams. The animals were grazed together from birth at the Whatawhata Hill Country Research Station.
There was a marked increase in weaning weight from the RCR (44.5 lb) to Fl (49.1 lb), a fall to the F2 (47.0 lb) , and then a further decline with continued interbreeding to the F3 (45.0 lb) and F4 (44.5 lb ) lambs. A similar trend was evident for lamb fleece weights. An increase of 1.3 Ib in fleece weight and 13.1 lb in October live weight was found between the RCR and Fl ewe hoggets, and a decline to the F3, which were 5.5 lb heavier and produced 0.3 lb more wool than the RCR.
Correction factors for birth-rearing rank, sex of lamb, and dam age are tabulated for each flock. Fleece weights were, overall, 0.61 lb higher for single- than for twin-born and reared lambs, 0.34 lb higher for twin-singles than for twins, and increased from 2-year-old to 4- and 5-year-old dams. There was little difference in lamb fleece weights between wether and ewe lambs. Weaning weight correction factors for birth-rearing rank were higher for crossbred than for Romney lambs, and those for sex were slightly lower for crossbreds. Overall, weaning weights were 1.6, 2.8, and 3.1 lb higher for 3-, 4-, and 5-year-old dams respectively than for 2-year-olds, and the regression of weaning weight on age was 0.29 lb/day.
Age of dam did not markedly affect ewe hogget fleece weight, but single and twin-reared hoggets differed, overall, by 0.4 lb. Correction factors derived for hogget live weight (420 days of age) were lower for age of dam and for birth-rearing rank than were those at weaning. The overall regression of weight on age was 0.23 lb/day,
