Relationships among Puberty,Muscle and Fat,and Liveweight Gain during Mating in Young Female Sheep |
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| Authors: | CA Rosales Nieto MB Ferguson H Thompson JR Briegel CA Macleay GB Martin AN Thompson |
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| Affiliation: | 1. CRC for Sheep Industry Innovation and the University of New England, Armidale, NSW, Australia;2. Department of Agriculture and Food of Western Australia, South Perth, WA, Australia;3. UWA Institute of Agriculture and School of Animal Biology, University of Western Australia, Crawley, WA, Australia;4. School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia;5. Moojepin MPM, Nyabing Rd Katanning, WA, Australia;6. Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, UK |
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| Abstract: | Greater depths of muscle are associated with better reproductive performance in ewe lambs, but, in adult ewes, reproductive performance also seems to vary with liveweight gain during the mating period. Therefore, in a large field study with Merino ewe lambs, we tested whether the relationships among eye muscle depth (EMD), fat depth (FAT) and reproductive performance depend on liveweight gain during the mating period. We selected lambs with a wide range in phenotypic values for depths of eye muscle (EMD) and fat (FAT) and assigned them to dietary treatments designed to achieve low (LOW, n = 244) or high (HIGH, n = 237) rates of liveweight gain during a 28‐day mating period. The LOW treatment maintained live weight, whereas the HIGH treatment gained 179 ± 3.8 g/day (p < 0.001). From those ewe lambs that attained puberty, first oestrus was detected at live weight 37.8 ± 0.2 kg and age 232 days. The proportion of ewes that attained puberty increased with EMD (p < 0.01). Ewes from the HIGH treatment were more fertile (pregnant ewes per 100 ewes exposed to rams) and had a higher reproductive rate (foetuses in utero per 100 ewes exposed to rams; p < 0.001) than those from the LOW treatment. Fertility and reproductive rate were positively correlated with weight gain during mating as well as live weight at the start of mating, FAT and EMD (p < 0.05 to <0.001). We conclude that faster growth, due to either extra nutrition during mating or higher phenotypic potential for fat and muscle, will increase reproductive performance in ewe lambs mated at 8 months of age. |
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