Abstract
Simple SummaryEwe replacements are a major cost in prime-lamb production. Many producers do not join replacements at 7 months as they believe that it has a negative effect on two-tooth performance. The effect of age at first joining on the reproductive performance of two-tooth ewes, representing three genotypes, was evaluated as well as the performance of their progeny. Whilst joining at 7 months reduced ewe body weight when joined at 19 months and immediately post joining, body weight at the subsequent lambing was increased, and ewe productivity and progeny performance were unaffected. Ewe genotype significantly influenced litter size and the number of lambs reared per ewe joined but had no effect on progeny performance. The probability of rearing at least one lamb (PR1L) is an indicator of overall efficiency. In the current study, whilst there was no relationship between ewe body weight when joined at 19 months and PR1L, there was a positive relationship between body weight at 7 months and PR1L at 2 years. It is concluded that joining replacements at 7 months does not have a negative impact on the performance of two-tooth ewes. The effects of first-joining age (7 or 19 months) and genotype on ewe performance when joined to lamb at 2 years, and the performance of their progeny, were evaluated using 424 ewes, representing 3 genotypes: Belclare (Bel), Suffolk × Belclare (Suf × Bel) and Suffolk-type (≥75% Suffolk ancestry (Suf75)). Ewes were managed in a grass-based system. Ewes first joined at 7 months were lighter (p < 0.01) at 19 months and immediately post lambing; otherwise, age at first joining had no effects (p > 0.05) on ewes or their progeny and there were no important interactions with genotype. Bel and Suf × Bel had larger litters (p < 0.001) and reared more lambs per ewe joined (p < 0.01) than Suf75. Ewe genotype had no effect (p > 0.05) on proportion failing to lamb, incidence of lambing assistance, lamb mortality, ewe survival to 31 months, or progeny performance. Increasing the body weight of ewes at 7 months of age increased the probability (p < 0.02) of rearing 1 or more lambs at 2 years and there was no interaction with genotype. It is concluded that age at first joining had no negative impact on the performance of ewes or their progeny.
Highlights
Replacement ewes represent a major cost in prime-lamb production and Keady [1] reported that the mean cost, nationally, of producing a replacement ewe, when joined for the first time at ~19 months, equated to approximately 25% of the value of her lifetime lamb-carcass output
Ewe genotype is a major determinant of prolificacy while age at first joining may affect the number of lamb crops per ewe lifetime
We have reported [2] that the productivity of replacements joined to lamb at 1 year depends on genotype: Belclare ewes reared 1.17 lambs per ewe joined compared with 0.82 for Suffolk-cross ewes of the type prevalent in lowland flocks in Ireland
Summary
Replacement ewes represent a major cost in prime-lamb production and Keady [1] reported that the mean cost, nationally, of producing a replacement ewe, when joined for the first time at ~19 months, equated to approximately 25% of the value of her lifetime lamb-carcass output. Two major determinants of the number of lambs reared per ewe lifetime are prolificacy and the number of lamb crops produced. Ewe genotype is a major determinant of prolificacy while age at first joining may affect the number of lamb crops per ewe lifetime. Most previous studies of the effect of age at first lambing on the performance at 2 years involved ewes of relatively low productivity and which lambed outdoors [4,5]. There is little information on the effects of age at first lambing on performance of two-tooth ewes representing genotypes differing widely in prolificacy and, level of productivity, and that are housed during mid and late pregnancy to facilitate higher stock carrying capacity in grass-based, prime-lamb systems
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