Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects

Accurate estimates of adjustment factors for systematic environmental effects are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate genetic parameters and investigate the significance of various environmental factors for production traits in Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, with over 2700 sires and 25 000 dams. Univariate linear mixed animal models were used to analyse 6 wool, 4 growth, and 4 reproduction traits. This first paper outlines the data structure and the non-genetic effects of age of the animal, age of dam, birth-rearing type, sex, flock, bloodline, and year, which were significant with few exceptions for all production traits. Age of dam was not significant for reproduction traits and fleece yield. Generally, wool, growth, and reproduction traits need to be adjusted for age, birth-rearing type, and age of dam before the estimation of breeding values for pragmatic and operational reasons. Adjustment for animal age in wool traits needs to be applied for clean fleece weight (CFW), greasy fleece weight (GFW), and fibre diameter (FD) with inclusion of 2 age groups (2 years old and >2 years old), but for reproduction traits, inclusion of all age groups is more appropriate. For GFW, CFW, and hogget weight (HWT), adjustment for only 2 dam age groups of maiden and mature ewes seems sufficient, whereas for birth (BWT), weaning (WWT), and yearling (YWT) weights, adjustments need to be applied for all dam age groups. Adjustment for birth-rearing type (single-single, multiple-single, multiple-multiple) is appropriate for wool, growth, and reproduction traits. The implications of adjustment for non-genetic effects are discussed.

Genetic and nutritional regulation of lamb growth and muscle characteristics

Combined actions of nutrition and genetic regulation of the growth rate of lambs as well as the physical, biochemical, and eating quality characteristics of their skeletal muscle were assessed in a major field experiment. Data arising were collated and integrated to consolidate findings made at the farm, animal, tissue, cellular, and gene expression levels. At the farm level, increased nutrient availability significantly increased the growth rate of crossbred lambs and increased the growth advantage resulting from the use of sires with high estimated breeding values (EBV) for growth. In contrast, the extra depth of the M. longissimus thoracis et lumborum (EMD) arising from sires with a higher EBV for this trait was constant irrespective of nutrition. Ewe liveweight and body condition were critical in determining the pre-weaning nutrition and growth of lambs, with the LOW plane of nutrition causing stunting of forelimb bones and changes to the allometric growth coefficients for carcass lean and fat. The EBV of the sire for muscling (PEMD) influenced several non-muscling traits, and interactions with nutrition suggested that on HIGH nutrition, absorbed nutrients were partitioned away from wool and fat accretion and towards protein accretion in lambs having superior muscling genetics. Expression levels of known myogenic factors in muscle, together with a suite of peptides and proteins whose identity and levels were determined by proteomic screening, contributed to improved understanding of the mechanisms underpinning nutritional and genetic regulation of skeletal muscle development. The study revealed the need for caution in the use of indirect markers of growth or composition, with their usefulness being constrained if the localisation of the response to selection is specific to parts of the carcass where the selection had initially been concentrated. As well, the possibility that much of the variation explained by potential physiological markers can be accounted for by non-invasive measures of growth and fatness currently used by Australian farmers must be considered.