Heritabilities and genetic correlations of body weight, testis growth and ewe lamb reproductive traits in crossbred sheep

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Abstract
Heritabilities (h2) and genetic correlations (rc) involving body weights, measures of testes size and ewe lamb reproduction were calculated using 953 spring-born lambs produced during formation of a three-breed composite population containing 0·50 Dorset, 0·25 Rambouillet and 0·25 Finnish Landrace breeding. The h2of body weight ranged from 0·2 to 0·3 between 45 and 150 days of age, but increased to 0·41 at the start of breeding of ewe lambs at about 6 months of age. Additive maternal effects were not important, perhaps because intensive housing encouraged cross-suckling. Testes size was measured as scrotal circumference (SC), SC with linear adjustment for weight (SCW) and SC divided by the one-third power of body weight (RSC). The h2of SC traits was highest at 90 days (0·52 for SC, 0·62 for RSC and 0·57 for SCW), and h2for age at maximum SC growth rate (i.e. TI, the inflexion point of a logistic SC growth curve) was 0·49. The h2of ewe lamb fertility in autumn was 0·09 but the h2for frequency of remating the following spring was 0·41. The h2for ewe lamb litter size in these data was zero. At 90 days, rcbetween alternative measures of testes size exceeded 0·86; rGwith body weight were 0·67 for SC, 0·53 for RSC and –0·74 for TI. The rGwith ewe lamb fertility for 90-day weight, SC, RSC and SCW and for TI were –0·25, 0·20, 0·25, 0·38 and –0·32, respectively. The rcfor these traits with spring remating were 0·34, 0·34, 0·26, 0·10 and –0·48, respectively.