Phenotypic and genetic parameters of productivity in Galway ewes

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Abstract
SUMMARY: Records from a selection flock of Galway ewes collected over a 6-yr period (1966 to 1971) were used to obtain estimates of the phenotypic and genetic parameters of ewe productivity. The number of lambs born (NLB) and weaned (NLW), the weight of lamb weaned (WLW), ewe body weight (EBW) and greasy fleece weight (GFL) were used as measures of productivity, mean values being 1·25, 0·88, 25·6 kg, 52·8 kg and 2·8 kg, respectively. Each ewe's annual performance was adjusted to a 4-yr-old ewe equivalent and expressed as a deviation from the appropriate flock × year subgroup mean; these deviations were combined into a single index value for each ewe for NLB, NLW and WLW. Records for 975 individual ewes representing 84 sires which had three or more progeny were used in a half sib analysis of variance.Estimates of heritability were 0·18, 0·24 and 0·25 for NLB, NLW and WLW based on index record and 0·07, 0·16 and 0·30 respectively for 2-yr-old ewes. Heritability estimates of EBW and GFL were 0·73 and 0·52 respectively. The genetic correlations between EBW and NLB2, NLW2, WLW2 and GFL were 0·85, 0·42, 0·62 and 0·53 respectively; those between EBW and index records were slightly negative. Phenotypic correlations were generally lower than the corresponding genetic ones.Ewes born as multiples were more productive than singles. They were 1·8 kg lighter (P < 0·01) at 18 mo and weaned 2·5 kg more lamb (P < 0·05) at 2 yr of age. The repeatability of NLB ranged from 0 to 0·2.