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    Effect of Breeding Heavier Romney Ewe Lambs at Seven Months of Age on Lamb Production and Efficiency over Their First Three Breeding Seasons
    (MDPI (Basel, Switzerland), 2021-12-07) Haslin E; Corner-Thomas RA; Kenyon PR; Pettigrew EJ; Hickson RE; Morris ST; Blair HT
    This experiment examined the effect of breeding heavier ewe lambs on lamb production and their efficiency over their first three breeding seasons. Two groups of ewe lambs were bred at seven months of age at an average pre-breeding live weight of either 47.9 ± 0.36 kg (heavy; n = 135) or 44.9 ± 0.49 kg (control; n = 135). Ewe live weight, number of lambs born and weaned, and lamb live weight were recorded until 39 months of age, and efficiency was calculated for each ewe. Although the number and lamb weaning weight did not differ between treatments over three years, when data were pooled, heavier ewe lambs at breeding weaned a greater number of lambs over the three-year period. The total lamb weaning weight over the three-year period increased by 2% for each additional kilogram at ewe lamb breeding. Breeding heavier ewe lambs had no effect on efficiency. These results suggest that although breeding heavier ewe lambs had a positive effect on lamb production over the three-year period, it had no effect on efficiency. Before final recommendations can be made, lifetime performance and longevity to five years of age of heavier ewe lambs at breeding are required.
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    Genetics of alternative definitions of feed efficiency in grazing lactating dairy cows
    (NZSAP, 7/07/2016) Hurley, AM; Lopez-Villalobos, N; McParland, S; Lewis, E; Kennedy, E; O'Donovan, M; Burke, JL; Berry, DP
    The objective of this study was to estimate genetic parameters for measures of energy conversion efficiency (ECE), energy balance (EB), net energy intake (NEI), net energy of lactation (NEL) and body weight (BW), within lactation stages in grazing dairy cows. Individual measurements of NEI (n=7,675) from 2,445 lactations on 1,245 grazing cows were available. Residual energy intake (REI) was defined as NEI minus predicted energy requirements; residual energy production (REP) was defined as net energy of lactation (NEL) minus predicted energy requirements. Energy conversion efficiency was defined as NEL divided by NEI; EB was defined as the difference between intake and energy required for maintenance plus lactation. Lactation was divided into three stages (8-90, 91-180, and >180 days in milk [DIM]). Genetic and phenotypic (co)variances for EB, NEL and BW were estimated using univariate and bivariate animal repeatability models. The models included the fixed effects of contemporary group (treatment and test-date), parity, DIM, as well as a random additive genetic effect of animal, a within-lactation stage random permanent environmental effect and an across-lactation permanent environmental effect. Heritability across-lactation stages varied from 0.13 (8-90 DIM) to 0.28 (91-180 DIM) for NEI, from 0.16 (8-90 DIM) to 0.33 (91-180 DIM) for NEL, from 0.04 (8-90 DIM) to 0.10 (91-180 and >180 DIM) for EB, from 0.03 (8-90 DIM) to 0.11 (>180 DIM) for REI, and from 0.04 (8-90 DIM) to 0.18 (>180 DIM) for ECE. A strong genetic association between REI and EB was evident when average BW change was close to zero. These genetic parameters from Holstein-Friesian dairy cows fed predominantly grazed grass imply that genetic improvement in selected efficiency traits is achievable.