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Browsing by Author "Mousel, Michelle R."

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    Effects of rearing triplet lambs on ewe productivity, lamb survival and performance, and future ewe performance
    Notter, David R.; Mousel, Michelle R.; Leeds, Timothy D.; Lewis, Gregory S.; Taylor, J. Bret (2018-12)
    Increasing prolificacy has been proposed to be the most effective way to increase the biological efficiency and profitability of sheep production. However, use of prolific breeds and genes with major effects on ovulation rate can increase prolificacy to levels that may not be desirable or sustainable in extensive rangeland production systems. This study thus evaluated effects of triplet births on ewe productivity and ewe and lamb performance. An initial study used 666 purebred Polypay litters to compare ewes with triplet litters that were required to raise all the lambs (Treatment A) with those whose triplet litters were reduced to 2 lambs (Treatment R). Adult Polypay ewes had an average litter size of 2.35 lambs per litter. The frequency of litters of 3 or more lambs was 43.2%; 56.0% of lambs were born in litters of 3 or more lambs. Ewes that had singles weaned fewer lambs and less body weight (BW) of lambs (P < 0.001; 0.94 lambs and 40.4 kg, respectively) than ewes that had twins or triplets. Ewes with triplet litters in Treatment A weaned more lambs (P < 0.01) and more BW of lambs (P < 0.05) than ewes that had triplets in Treatment R (2.13 lambs and 62.9 kg, respectively, vs. 1.79 lambs and 55.0 kg, respectively), and weaned more lambs than ewes that had twins (1.77 lambs; P < 0.01). However, neither group of triplet-bearing ewes weaned more BW of lambs than ewes that had twins (58.9 kg; P >= 0.34). In 2 sets of data involving 442 purebred Polypay litters and 987 litters from Polypay or Romanov-White Dorper x Rambouillet ewes mated to terminal sires, ewes were required to raise all triplet-born lambs. Death losses for triplets in these studies (39.6 and 31.6%, respectively) were higher than those in Treatment A of the initial study (26.2%), resulting in greater numbers of lambs weaned for triplet, compared to twin, litters (1.79 vs. 1.68, respectively; P = 0.02) but no greater weight of lambs weaned (54.3 vs. 55.4 kg, respectively; P = 0.17). Based on these 3 sets of data, ewes that were required to rear triplet lambs weaned 0.20 more lambs per litter than ewes that had twins but also had 0.75 additional dead lambs per litter, and thus a lamb mortality overhead of 3.75 additional dead lambs for each additional weaned lamb. We conclude that there is an intermediate optimum prolificacy level for extensive rangeland production systems. If optimum prolificacy is exceeded, removal and artificial rearing of surplus lambs are necessary to avoid increased lamb death losses.
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    Evaluation of Rambouillet, Polypay, and Romanov-White Dorper x Rambouillet ewes mated to terminal sires in an extensive rangeland production system: bode weight and wool characteristics
    Murphy, Thomas W.; Stewart, Whitney C.; Notter, David R.; Mousel, Michelle R.; Lewis, Gregory S.; Taylor, J. Bret (2019-04)
    Though lamb sales account for the majority of annual receipts on U.S. sheep operations, wool is an important income source for many Western flocks. Crossing fine-wool sheep with prolific or composite hair sheep breeds can increase lamb production, but fleece quality and marketability may be reduced by a greater content of nonwool fibers (e.g., med and kemp). The objectives of this study were to compare BW and wool characteristics of Rambouillet, Polypay, and Romanov-White Dorper x Rambouillet (RW-RA) ewes under extensive rangeland management conditions. Ewe BW was collected before mating (fall) and 30 d postlambing (spring) each year from 1 yr up to 4 yr of age. In spring and fall, Rambouillet and Polypay ewes were similar in BW (P >= 0.94). Spring BW did not differ (P = 0.13) between RW-RA and Polypay, but Rambouillet ewes were heavier than RW-RA in the spring (P = 0.02). Both Rambouillet and Polypay ewes were heavier Rambouillet, intermediate in Polypay, and greatest in RW-RA (P < 0.01). Wool from RW-RA ewes had greater %M, %K, and %T (P < 0.001) than wool from Rambouillet and Polypay ewes, which were not different (P > 0.99). Results indicated superior wool production for Rambouillet compared (P < 0.07) than RW-RA in the fall. Greasy fleece weight and mid-side wool samples were collected from ewes at 1 and 4 yr of age. Clean fleece weights (CFW) were estimated from average laboratory scoured yield of mid-side wool samples composited within-breed. Average fiber diameter (AFD), SD of fiber diameter (SD-FD), and percentage med (%M), kemp (%K), and total medullated fibers (%T) were quantified on individual mid-side wool samples. There was no difference in 1-yr-old CFW among breed types (P >= 0.96). Four-yr-old Rambouillet ewes had heavier CFW (2.29 kg; P < 0.001) than 4-yr-old Polypay (1.83 kg) and RW-RA ewes (1.86 kg), which were not different (P > 0.99). Within 1- and 4-yr-olds, AFD differed among breed type (P < 0.001) and was the finest for Rambouillet (20.1 and 21.9 mu m, respectively), intermediate for RW-RA (22.8 and 24.8 mu m), and coarsest for Polypay (24.2 and 26.7 mu m). Also within 1-and 4-yr olds, SD-FD was lowest in with the coarser, more variable wool produced by Polypay and RW-RA. Still, past research reported greater lamb production in Polypay and RW-RA ewes which, under recent market conditions, would be associated with greater annual gross revenue for these breed types than for Rambouillet.
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    Evaluation of Rambouillet, Polypay, and Romanov-White Dorper x Rambouillet ewes mated to terminal sires in an extensive rangeland production system: Lamb production
    Notter, David R.; Mousel, Michelle R.; Lewis, Gregory S.; Leymaster, K. A.; Taylor, J. Bret (2017-09)
    Ewe productivity (i. e., total number or weight of lambs weaned per breeding ewe) is a key indicator of lamb production efficiency. This study compared various measures of ewe productivity and ewe and lamb performance among ewes of 3 breed types mated to rams of 4 terminal-sire breed types in an extensive rangeland production system. Purebred Rambouillet (n = 212), purebred Polypay (n = 236), and crossbred Romanov-White Dorper x Rambouillet (RW-RA; n = 231) ewes were produced from locally adapted Polypay and Rambouillet ewes and then annually mated to Columbia, Suffolk, Columbia x Suffolk, or Suffolk x Columbia sires for up to 4 yr, beginning at 1 yr of age. The cumulative number and weight of lambs weaned through 4 yr were greater for RW-RA (5.9 lambs and 153 kg, respectively) and Polypay ewes (4.9 lambs and 123 kg, respectively) than for Rambouillet ewes (2.9 lambs and 99 kg, respectively) and also were greater for RW-RA ewes than for Polypay ewes (all P < 0.001). Greater productivity of RW-RA and Polypay ewes, compared with Rambouillet ewes, was driven by greater lambing rates (ewes lambing per ewe exposed) as ewe lambs (87 and 77 vs. 31%, respectively; P < 0.001) and greater (P < 0.001) litter sizes as ewe lambs (1.3, 1.3, and 1.0, respectively) and adult ewes (2.1, 2.0, and 1.6, respectively). The RW-RA ewes also had greater longevity (P < 0.01) and cumulative lambing rates (P < 0.001) than Polypay and Rambouillet ewes. Lamb BW at birth and weaning in adult ewes favored less-prolific Rambouillet ewes (P < 0.001), but after adjustment for type of birth and rearing and weaning age, differences in weaning BW among ewe breed types were small and not significant (P = 0.08). Effects of sire breed type on measures of cumulative ewe productivity were not significant (P > 0.74), but Suffolk-sired lambs had the heaviest adjusted birth weights (P = 0.01) and Columbia-sired lambs tended to have the lightest adjusted weaning weights (P = 0.12). Combined effects of heterosis and additive breed effects were associated with greater lambing rates in ewe lambs, larger litters at all ages, and substantially greater number and weight of lambs weaned for Polypay and RW-RA ewes than for Rambouillet ewes.
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    Model definition for genetic evaluation of purebred and crossbred lambs including heterosis
    Jurado, Napoleon Vargas; Notter, David R.; Taylor, Joshua B.; Brown, Daniel J.; Mousel, Michelle R.; Lewis, Ronald M. (Oxford University Press, 2022-06)
    Both direct and maternal heterosis increase birth and post-natal weights in crossbred lambs. Estimates of these heterotic effects can be used as adjustment factors in multi-breed genetic evaluations. Crossbreeding is a common practice among commercial sheep producers to improve animal performance. However, genetic evaluation of U.S. sheep is performed within breed type (terminal sire, semi-prolific, and western range). While incorporating crossbred records may improve assessment of purebreds, it requires accounting for heterotic and breed effects in the evaluation. The objectives of this study were to: 1) describe the development of a paternal composite (PC) line, 2) determine the effect of direct and maternal heterosis on growth traits of crossbred lambs, 3) estimate (co)variance components for direct and maternal additive, and uncorrelated maternal environmental, effects, and 4) provide an interpretation of the estimates of random effects of genetic groups, and to use those solutions to compare the genetic merit of founding breed subpopulations. Data included purebred and crossbred records on birth weight (BN; n = 14,536), pre-weaning weight measured at 39 or 84 d (WN; n = 9,362) depending on year, weaning weight measured at 123 d (WW; n = 9,297), and post-weaning weight measured at 252 d (PW; n = 1,614). Mean (SD) body weights were 5.3 (1.1), 16.8 (3.9) and 28.0 (7.6), 39.1 (7.2), and 54.2 (8.7) kg for BN, WN (at the two ages), WW, and PW, respectively. In designed experiments, the Siremax, Suffolk, Texel, Polypay, Columbia, Rambouillet, and Targhee breeds were compared within the same environment. Estimates of heterotic effects and covariance components were obtained using a multiple trait animal model. Genetic effects based on founders' breeds were significant and included in the model. Percent estimates of direct heterosis were 2.89 +/- 0.61, 2.60 +/- 0.65, 4.24 +/- 0.56, and 6.09 +/- 0.86, and estimates of maternal heterosis were 1.92 +/- 0.87, 4.64 +/- 0.80, 3.95 +/- 0.66, and 4.04 +/- 0.91, for BN, WN, WW, and PW, respectively. Correspondingly, direct heritability estimates were 0.17 +/- 0.02, 0.13 +/- 0.02, 0.17 +/- 0.02, and 0.46 +/- 0.04 for BN, WN, WW, and PW. Additive maternal effects accounted for trivial variation in PW. For BN, WN, and WW, respectively, maternal heritability estimates were 0.16 +/- 0.02, 0.10 +/- 0.02, and 0.07 +/- 0.01. Uncorrelated maternal environmental effects accounted for little variation in any trait. Direct and maternal heterosis had considerable impact on growth traits, emphasizing the value of crossbreeding and the need to account for heterosis, in addition to breed effects, if crossbred lamb information is included in genetic evaluation. Lay Summary Crossbreeding is common in commercial sheep enterprises. It allows breeds with different attributes to be combined to generate crossbred progeny tailored to production environments and customer preferences. Additionally, crossbreds often benefit from heterosis, performing at levels above the average of their parental breeds. Over two decades, body weights were collected at birth and at pre-weaning, weaning, and post-weaning ages on purebred and crossbred lambs from semi-prolific (Polypay), western range (Columbia, Rambouillet, Targhee), and terminal sire (Siremax, Suffolk, Texel) breeds at the U.S. Sheep Experiment Station. When combined, the value of direct heterosis-that due to a lamb being crossbred-and maternal heterosis-that due to the lamb's dam being crossbred-increased birth (5%) and post-natal (up to 10%) weights in crossbred lambs. This highlights the value of crossbreeding to the U.S. sheep industry, especially in western range production systems. Genetic variation between and within breeds also was detected for the purebred parental breeds. Such heterotic and breed effects must be accounted for if crossbred performance is to be incorporated in genetic evaluation of purebreds. Therefore, these results provide the foundation for utilizing crossbred information in the evaluation and selection of purebred sheep in the United States.