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Author: search.filters.author.Kenyon PRSubject: search.filters.subject.ovine

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    Genetic Trends for Production and Reproduction Traits in Ultrafine Merino Sheep of Uruguay
    (John Wiley and Sons Ltd, 2025-03-21) Ramos Z; Garrick DJ; Blair HT; De Barbieri I; Ciappesoni G; Montossi F; Kenyon PR
    Genetic trends were estimated for production and reproduction traits in an Uruguayan Merino genetic nucleus. Two consecutive periods with different selection objectives were studied. During the first period (1999–2010), the selection objective of this flock focused on reducing fibre diameter (FD), while allowing for a slight loss in clean fleece weight (CFW). From 2011 to 2018, the breeding objective was shifted and then focused on maintaining FD, while increasing both CFW and live weight (LW). Data from approximately 5380 yearling lambs and 2000 ewes born between 1999 and 2018 were analysed. Genetic trends were estimated for yearling and adult FD (Y_FD and A_FD, respectively), yearling and adult CFW (Y_CFW and A_CFW, respectively), yearling LW (Y_LW), 2-year-old ewe mating live weight and mating body condition score (2-yo_LWM and 2-yo_BCSM, respectively) and the number of lambs weaned per ewe joined (NLWEJ). Estimated breeding values were predicted to calculate genetic trends for the two periods of selection. From 1999 to 2010, yearling lambs showed significant reductions in FD (−0.210 μm/year, corresponding to −1.28% of the mean of the trait for that period). Before 2010, yearling lambs showed reductions of −0.013 kg/year (−0.62%) in CFW, whereas from 2011 to 2018, this trait increased by 0.052 kg/year (1.88%). The annual genetic gain for Y_LW was greater in the second period than in the first period (0.286 vs. 0.091 kg/year). The genetic trends for FD, CFW and LW were affected by period (p < 0.001), indicating that the change in the selection index applied in the genetic nucleus was effective. Over the entire study period (1999–2018), the total genetic responses for 2-yo_BCSM and NLWEJ were near zero. These results indicate that the breeding programme utilised in the genetic nucleus improved the traits under selection (FD, CFW and LW) and had a marginal impact on 2-yo_BCSM and NLWEJ. To also achieve relevant genetic gains in ewe reproductive performance, in the future, reproduction traits should be incorporated into the selection programme for Uruguayan fine-wool sheep. The results obtained in this study will be used to refine the breeding programmes for Merino sheep in Uruguay.
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    Factors Associated with Ewe Death and Casting in an Extensively Farmed Sheep Flock in New Zealand
    (MDPI (Basel, Switzerland), 2021-12) Capdevila-Ospina K; Corner-Thomas RA; Flay KJ; Kenyon PR; Ridler AL; Garcia Ispierto I
    Ewe deaths affect the productivity and profitability in sheep farming systems and have potential animal welfare and market perception implications. Internationally, there is scant data on the timing and causes of ewe deaths in extensive grazing systems. There is no published literature on the incidence and risk factors associated with casting (ewe in late gestation accidentally immobilised, often in dorsal recumbency). This study, undertaken using a cohort of 1789 ewes on a New Zealand farm, reports on the timing and risk factors associated with production parameters for ewe deaths through an almost two-year period, along with causes of death during both peripartum periods. Ewe deaths occurred throughout both years but were most frequent during the peripartum (pre-lambing to mid-lactation) period. Casting was the most commonly identified cause of death in both years, responsible for approximately a quarter to a third of potential annual mortality. Few risk factors for death or casting were identified. In conclusion, the peripartum period is a high-risk time period for ewe deaths (and, by extension, will also contribute to lamb perinatal mortality). In extensively grazed flocks where casting events occur, it is recommended that all ewes are monitored daily during the peripartum period.