Genetics and Breeding

Genetic parameters for a range of sheep production traits have been reviewed from estimates published over the last decade. Weighted means and standard errors of estimates of direct and maternal heritability, common environmental effects and the correlation between direct and maternal effects are presented for various growth, carcass and meat, wool, reproduction, disease resistance and feed intake traits. Weighted means and confidence intervals for the genetic and phenotypic correlations between these traits are also presented. A random effects model that incorporated between and within study variance components was used to obtain the weighted means and variances. The weighted mean heritability estimates for the major wool traits (clean fleece weight, fibre diameter and staple length) and all the growth traits were based on more than 20 independent estimates, with the other wool traits based on more than 10 independent estimates. The mean heritability estimates for the carcass and meat traits were based on very few estimates except for fat (27) and muscle depth (11) in live animals. There were more than 10 independent estimates of heritability for most reproduction traits and for worm resistance, but few estimates for other sheep disease traits or feed intake. The mean genetic and phenotypic correlations were based on considerably smaller numbers of independent estimates. There were a reasonable number of estimates of genetic correlations among most of the wool and growth traits, although there were few estimates for the wool quality traits and among the reproduction traits. Estimates of genetic correlations between the groups of different production traits were very sparse. The mean genetic correlations generally had wide confidence intervals reflecting the large variation between estimates and relatively small data sets (number of sires) used. More accurate estimates of genetic parameters and in particular correlations between economically important traits are required for accurate genetic evaluation and development of breeding objectives. more »

Data from seven research resource flocks across Australia were combined to provide accurate estimates of genetic correlations among production traits in Merino sheep. The flocks represented contemporary Australian Merino fine, medium and broad wool strains over the past 30 years. Over 110,000 records were available for analysis for each of the major wool traits, and 50,000 records for reproduction and growth traits with over 2700 sires and 25,000 dams. Individual models developed from the single trait analyses were extended to the various combinations of two-trait models to obtain genetic correlations among six wool traits [clean fleece weight (CFW), greasy fleece weight, fibre diameter (FD), yield, coefficient of variation of fibre diameter and standard deviation of fibre diameter], four growth traits [birth weight, weaning weight, yearling weight (YWT), and hogget weight] and four reproduction traits [fertility, litter size, lambs born per ewe joined, lambs weaned per ewe joined (LW/EJ)]. This study has provided for the first time a comprehensive matrix of genetic correlations among these 14 wool, growth and reproduction traits. The large size of the data set has also provided estimates with very low standard errors. A moderate positive genetic correlation was observed between CFW and FD (0.29 +/- 0.02). YWT was positively correlated with CFW (0.23 +/- 0.04), FD (0.17 +/- 0.04) and LWEJ (0.58 +/- 0.06), while LW/EJ was negatively correlated with CFW (-0.26 +/- 0.05) and positively correlated with FD (0.06 +/- 0.04) and LS (0.68 +/- 0.04). These genetic correlations, together with the estimates of heritability and other parameters provide the basis for more accurate prediction of outcomes in complex sheep-breeding programmes designed to improve several traits. more »

Reproductive physiology and procreation has always fascinated human kind. Therefore, it is not surprising that scientific research in reproduction is one of the oldest and most established field in biology. Advancement in reproductive sciences has been possible because of the curiosity of scientists of various backgrounds (biologists, animal scientists, and veterinarians). At the turn of the twentieth century, advances in reproductive research were mostly driven by needs for improved animal production and prevention of venereal diseases. The body of knowledge in animal reproduction has seen an exponential growth in the last 50 years. In recent years, the field of study expanded beyond laboratory species and production animals to include wildlife conservation and management. As this field of research grew, scientists felt the importance of organizing in international societies dedicated to this area. One of the oldest of these societies is the Society for the Study of Reproduction. In the veterinary field, reproductive physiology and pathology became known as “Theriogenology” thanks to the efforts of the founding members of a veterinary specialty under the name of the American College of Theriogenologists, recognized in 1971 by the American Veterinary Medical Association as an integral part of the veterinary curriculum (1). Similar specialty colleges were also started in Europe (European College of Animal Reproduction), Australia, and New Zealand (College of Veterinary Scientists, Animal Reproduction). In addition to these specialty colleges, other international societies have emerged including Society for Theriogenology, International Embryo Transfer Society, European Society for Domestic Animal Reproduction, and European Society for Small Animal Reproduction. All these society have now well-established regular meetings to provide a forum for communication of recent research and their application to the health and welfare of animals. This paper attempts to highlight some of the major milestones and challenges in reproductive research. more »

The quality and quantity of alpaca fibre is affected by not only the body condition and nutrition of the animal but also by season and sex hormones. These factors can interact with the genetic potential of each animal to such an extent that they can mask the true genetic value of an animal. This RIRDC report provides scientific data that can be used by producers, consultants to the industry, and feed manufacturers to design more appropriate diets and feeding strategies that will allow the industry to make genetic progress because these management procedures will decrease the impact of nutritional and environmental factors on the expression of the animal’s genetic potential for fibre production. more »