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Selection for superior growth advances the onset of puberty and increases reproductive performance in ewe lambs

Published online by Cambridge University Press:  08 February 2013

C. A. Rosales Nieto ,
M. B. Ferguson ,
C. A. Macleay ,
J. R. Briegel ,
G. B. Martin  and
A. N. Thompson
C. A. Rosales Nieto
Affiliation:
CRC for Sheep Industry Innovation and the University of New England, Armidale, NSW 2351, Australia Department of Agriculture and Food of Western Australia, 3 Baron Hay Court, South Perth, Western Australia 6151, Australia Institute of Agriculture, University of Western Australia, Crawley, Western Australia 6009, Australia
M. B. Ferguson
Affiliation:
CRC for Sheep Industry Innovation and the University of New England, Armidale, NSW 2351, Australia Department of Agriculture and Food of Western Australia, 3 Baron Hay Court, South Perth, Western Australia 6151, Australia School of Veterinary and Biomedical Sciences, Murdoch University, 90 South Street, Murdoch, Western Australia 6150, Australia
C. A. Macleay
Affiliation:
Department of Agriculture and Food of Western Australia, 3 Baron Hay Court, South Perth, Western Australia 6151, Australia
J. R. Briegel
Affiliation:
Department of Agriculture and Food of Western Australia, 3 Baron Hay Court, South Perth, Western Australia 6151, Australia
G. B. Martin
Affiliation:
Institute of Agriculture, University of Western Australia, Crawley, Western Australia 6009, Australia
A. N. Thompson*
Affiliation:
CRC for Sheep Industry Innovation and the University of New England, Armidale, NSW 2351, Australia Department of Agriculture and Food of Western Australia, 3 Baron Hay Court, South Perth, Western Australia 6151, Australia School of Veterinary and Biomedical Sciences, Murdoch University, 90 South Street, Murdoch, Western Australia 6150, Australia
*
†E-mail: [email protected]
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Abstract

The reproductive efficiency of the entire sheep flock could be improved if ewe lambs go through puberty early and produce their first lamb at 1 year of age. The onset of puberty is linked to the attainment of critical body mass, and therefore we tested whether it would be influenced by genetic selection for growth rate or for rate of accumulation of muscle or fat. We studied 136 Merino ewe lambs with phenotypic values for depth of eye muscle (EMD) and fat (FAT) and Australian Sheep Breeding Values at post-weaning age (200 days) for live weight (PWT), eye muscle depth (PEMD) and fat depth (PFAT). First oestrus was detected with testosterone-treated wethers and then entire rams as the ewes progressed from 6 to 10 months of age. Blood concentrations of leptin and IGF-I were measured to test whether they were related to production traits and reproductive performance (puberty, fertility and reproductive rate). In total, 97% of the lambs reached first oestrus at average weight 39.4 ± 0.4 kg (mean ± s.e.m.) and age 219 days (range 163 to 301). Age at first oestrus decreased with increases in values for PWT (P < 0.001), and concentrations of IGF-I (P < 0.05) and leptin (P < 0.01). The proportion of ewe lambs that achieved puberty was positively related with increases in values for EMD (P < 0.01), FAT (P < 0.05) or PWT (P < 0.01), and 75% of the ewe lambs were pregnant at average weight 44.7 ± 0.5 kg and age 263 days (range 219 to 307). Ewe lambs that were heavier at the start of mating were more fertile (P < 0.001) and had a higher reproductive rate (P < 0.001). Fertility and reproductive rate were positively correlated with increases in values for EMD (P < 0.01), FAT (P < 0.05), PWT (P < 0.01) and leptin concentration (P < 0.01). Fertility, but not reproductive rate, increased as values for PFAT increased (P < 0.05). Leptin concentration increased with increases in values for EMD (P < 0.001), FAT (P < 0.001), PWT (P < 0.001), PEMD (P < 0.05) and PFAT (P < 0.05). Many of these relationships became non-significant when PWT or live weight was added to the statistical model. We conclude that selection for genetic potential for growth can accelerate the onset of puberty and increase fertility and reproductive rate of Merino ewe lambs. The metabolic hormones, IGF-I and leptin, might act as a physiological link between the growing tissues and the reproductive axis.

Keywords

ewe lambsphenotypic selectionASBVreproductive efficiency
Type
Physiology and functional biology of systems
Information
animal , Volume 7 , Issue 6 , June 2013 , pp. 990 - 997
Copyright
Copyright © The Animal Consortium 2013

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