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This paper reports genetic parameters for lamb survival and mortality traits on sheep farms in New Zealand. Lamb survival and mortality records were obtained from 38 flocks (103,357 lambs) from 5 yr of lambing data (2007 to 2011) and include many breeds and their crosses (predominantly Romney, Perendale, Coopworth, and Texel). A number of models were tested, all including environmental weather effects and investigating the random environmental effect of dam and litter (dam/year) as well as logit transformation for binary traits. Total heritability (direct + maternal) estimates were low for lamb viability at birth (0.01), lamb death risk to dystocia (0.01), and lamb death risk to starvation exposure (0.01) from birth to 3 d of age in an analysis accounting for direct and maternal genetic effects and the maternal environmental effects. Lamb survival heritabilities reported are very low (total heritabilities range from 0.02 to 0.06). The total heritabilities for the lamb death risk traits are lower than reported estimates of survival to 3 d of age or to weaning suggesting selection for the postmortem traits are not warranted at this time within these flocks. The total heritability for lamb birth weight was moderate (0.38) and the genetic correlations with the lamb death risk traits suggested that directional selection on lamb birth weight would have an effect on survival, although it is likely to have a nonlinear effect and therefore an optimum birth weight at which survival is maximized. This study has also shown that the total heritabilities may be overestimated when not accounting for maternal genetic and environment effects and in particular not accounting for the random environmental effect of litter (dam/year). [ABSTRACT FROM AUTHOR]

This work investigated effects of carrying 0, 1, or 2 copies of the A allele resulting from the g+ 6723C-A transition in growth differentiation factor gene (GDF8) in New Zealand Texel-cross sheep at different lamb ages and carcass weights. Two Texel-cross sires carrying 1 copy of the A allele were mated to approximately 200 ewes carrying 0, 1, or 2 copies of the A allele. A total of 187 progeny were generated and genotyped to determine whether they were carrying 0, 1, or 2 copies of the A allele. The progeny were assigned to 1 of 4 slaughter groups balanced for the 3 genotypes, sex, and sire. The 4 groups were slaughtered commercially when their average BW (across all progeny in the slaughter group) reached 33, 40, 43, and 48 kg, respectively. Measurements of BW, and carcass dimensions arid yield were made on all animals using Viascan (a commercial 2-dimensional imaging system that estimates lean content of the carcass as a percentage of total carcass weight). Additional measurements were made on the fourth slaughter group, which was computed tomography scanned at each slaughter time point to obtain 4 serial measures of lean and fat as estimated from the computed tomography images, The A allele did not have an effect on any BW traits. The A allele was associated with increased muscle and decreased fat across the variety of measures of muscling and fat, explaining between 0.2 and 1.1 of a residual SD unit. Estimates for an additive effect were significant and were positive for muscle and negative for fat traits. No dominance effect estimates (positive or negative) were significant. There was no significant interaction between A allele number and carcass weight or slaughter group for any trait. This is the first systematic study of the effect of the A allele copy number over a range of carcass weights (13 to 20 kg) and ages and results suggest the size of the effect across these endpoints is proportionately the same. Testing for the A allele therefore offers breeders the potential to improve rates of genetic gain for lean-meat yield across most production systems. [ABSTRACT FROM AUTHOR]

The objective of this study was to deter- mine whether differences in mRNA levels of key pituitary genes that regulate GH production, pituitary development, and growth were present and/or associated with divergent body composition phenotypes observed between sheep from genetically divergent lean and fat selection lines. Real-time PCR transcription profiles for pituitary specific transcription factor 1, prophet of pit 1, GH, GH receptor, GH secretagogue receptor, GHRH receptor, leptin receptor, and somatostatin receptors 1 and 2 were determined in pituitary tissue. There was a difference in the amount of both GH (P < 0.001) and GH secretagogue receptor (P < 0.001) mRNA between the selection lines (5 females and 5 males per line; 20 wk of age); the lean line had greater abundance than the fat line, irrespective of which endogenous control gene was used. The results obtained for GHRH receptor were equivocal but suggestive; there were greater GHRH receptor mRNA levels (P < 0.001) in the lean line using beta-2-microglobulin as the endogenous con- trol but not when hypoxanthine phosphoribosyltransferase and glyceraldehyde-3-phosphate dehydrogenase were used. No difference in pituitary specific transcription factor 1, prophet of pit 1, GH receptor, leptin receptor, or somatostatin receptors 1 and 2 mRNA concentration was observed between the lines. The greater abundance of GH mRNA in the pituitary somatotropes from genetically lean animals appears to be associated with increased levels of GH secretagogue receptor mRNA and possibly GHRH receptor mRNA. This suggests that the difference in GH secretion between the lines may be due to differences in the afferent signals, such as ghrelin and/or GHRH, arising from the hypothalamus, or as a result of differential pituitary sensitivity to these hormones. [ABSTRACT FROM AUTHOR]