Lamb Production and Its Components in Pure Breeds and Composite Lines. II. Breed Effects and Heterosis

Abstract

Ewe performance was compared for five pure breeds of sheep (Finnsheep, F; Rambouillet, R; Dorset, D; Targhee, T; Suffolk, S) and the crosses in development of two maternal composite lines (C1 = 1/2F1/4R1/4D and C2 = 1/2F1/4T1/4S). The data involved 10,959 breeding season records of 4,219 ewes by 412 sires. Ewe production and the components (fertility, litter size, neonatal and preweaning lamb survival and mean lamb weaning weight) were adjusted for age and standardized across season of lambing and years. The D and F ewes produced more weight of lamb/ewe exposed than R, S and T ewes because of higher D and F fertility, higher D lamb survival and larger F litters. First cross and inter se generations of C1 and C2 ewes averaged 17 to 27% higher fertility than the parental mean. Litter size averaged about one lamb higher for F than for other pure breeds, but only slightly higher for C1 and C2 than for the mean of F and other breeds. Lower neonatal survival for F than for other breeds and crosses was associated with the larger F litters and with 2 to 8% positive heterosis in the crosses. Preweaning survival of suckled and nursery lambs was low for F and S and positive heterosis ranged from 9 to 19% in crosses. Mean lamb weaning weights were highest for S, lowest for F, with little heterosis in crosses. Crossbred ewes reared .3 to .4 more lambs than mean for parental pure breeds. Heterosis in C1 and C2 ranged from 11 to 28% for lambs born, 27 to 43% for lambs weaned and 29 to 44% for weight of lamb weaned/ewe exposed. Decline in heterosis with inter se mating of crosses was no greater than expected from the reduction in predicted heterozygosity.

Comparison of the longevity and lifetime performance of Scottish Blackface ewes and their crosses within hill sheep flocks

“…Retaining crossbred ewes sired by lowland-type breeds, which have been selected under less harsh conditions, may result in reduced hardiness and longevity when compared with the traditional hill breed types (Hohenboken and Clarke, 1981). On the other hand, heterosis for survival and 'fitness' traits may be expressed in crossbred ewes (Fogarty et al, 1984;Simm et al, 1994) which could benefit their longevity and lifetime performance.…”

Genetic parameters of reproductive traits in sheep

“…Variability of some composite traits, such as NLWEE and TLWWEE, is strongly influenced by other basic or composite traits, such as CR, NLAW and NLB (Fogarty et al, 1985). Variability due to CR, NLB and NLAW may have a large influence on other traits when they are expressed in poor management.…”

“…Selection for LMWLW will result in heavier lambs at weaning, but the total productivity of the ewe is the total kilogram of lamb produced at weaning. Litter mean weight per lamb born can be used for selection to have lambs that will survive to weaning, because there is a high phenotypic correlation between weight at birth and survival (Fogarty et al, 1984b).…”

Effects of breed and age on the performance of crossbred hill ewes sourced from Scottish Blackface dams

“…Cheviot (CH)) is one method that can be used to manipulate flock genetics, but this strategy can be costly to implement (Simm et al, 1994) and may have limited performance benefits (Carson et al, 2001). An alternative method is through crossbreeding, which provides opportunities to introduce complementary traits for prolificacy and lamb growth, and also to exploit heterosis for reproduction, survival and 'fitness' traits (Fogarty et al, 1984;Simm et al, 1994). In recent years, considerable research has been undertaken to quantify the benefits of using crossbred females within the lowland sector Carson, 2002a and2002b;Dawson et al, 2002;Carson et al, 2004).…”