Tenderness is one of the major meat quality factors that affects the intent of consumers to re-purchase beef. Both genetic and non-genetic factors affect the quantitative trait of tenderness. Among the genetic factors, polymorphisms in key genes, such as the myostatin (MSTN) and calpain 1(CAPN1), play important roles on tenderness. However, these genes do not explain all the genetic variation associated with tenderness. The aim of this study was to discover additional genes associated with tenderness to help integrate genetic information into beef cattle breeding programmes and meat quality assurance programmes, such as Meat Standards Australia, and produce high quality tender meat for consumers. Discovery of such genes should also aid in the understanding of mechanisms underlying tenderness. Backcross QTL mapping progeny based on crosses between two extreme Bos Taurus breeds (Limousin and Jersey) were used in the study. There were four new traits created for the QTL mapping and association studies. Two of the traits (wbld_adjusted and wbst_adjusted) were based on Warner-Bratzler (WB) shear force measurements from the M. longissimus dorsi (LD) and M. semitendinosus (ST) muscles and were derived from a multi-variate mixed model in which the environmental effects, myostatin F94L genotype effect, ageing day effect and the interaction effects were accounted for. The adjusted shear force traits offered a more accurate prediction for average tenderness. The other new trait was the amount of ageing per 25 days (called "ageing rate" herein) for the two muscles, calculated as the difference between natural log shear force values after 1 and 26 days ageing. Quantitative trait loci (QTL) mapping for these traits indicated there were 2 QTL (92 cM on BTA 5 and 52 cM on BTA 29) for adjusted shear force of the LD muscle, 3 QTL (96 cM on BTA 5, 36 cM on BTA 18 and 52 cM on BTA 29) for adjusted shear force of the ST muscle, 2 QTL (40 cM on BTA 4 and 0 cM on BTA 13) for ageing rate of the LD muscle and 2 QTL (48 cM on BTA 1 and 44 cM on BTA 19) for ageing rate of the ST muscle. Twelve candidate genes were selected for further study based on their physiological functions and the QTL mapping results from herein and elsewhere. Twenty DNA variants in these candidate genes were chosen for the association studies. The analyses were conducted with and without three known tenderness related gene variants (MSTN F94L, CAPN1-SNP316 and CAPN1-SNP530). Variants in the candidate genes were discovered to be significantly associated with traits related to tenderness, most of which were muscle specific effects. Of note, the effects of CAPN1-SNP316 were muscle specific. The heterozygous genotype (GC) of CAPN1-SNP316 had the opposite effect on LD and ST muscles in that the G allele was dominant for the LD but recessive for the ST. Another variant of large effect, MYO1G-SNP2 (myosin 1G), showed an effect on ageing rate of the LD muscle but not the ST muscle. Importantly, however, the interactions between gene variants frequently explained more of the genetic variation than the individual variants. For example, the interaction between the candidate gene variant SNIP1-SNP3 (Smad nuclear interacting protein 1) and the CAPN1-SNP316 explained more of the variation in the adjusted shear force of the ST muscle than CAPN1-SNP316 alone (9.5% vs. 5.2%). The studies also suggest that tenderness is not always affected by the genes that change the muscle weight or collagen content (eg. insulin-like growth factor 1). In fact, the results indicate that the effect of the myostatin gene on tenderness is not caused by the increased muscle mass or collagen changes associated with the myostatin F94L variant. Instead, most of the effect of myostatin on tenderness may be explained by a change in the muscle fibre types which affects calpain activity.

Since the time of domestication more than 10,000 years ago, cattle have played an increasingly crucial role in the development of human civilizations. Progress has been quite remarkable since the turn of the century; the sequencing of the bovine genome in 2009 launched new avenues for furthering our understanding of theoretical and practical aspects of cattle genetics. Covering a vast array of questions, this book reviews major topics from molecular and developmental genetics, disease resistance and immunogenetics to genetic improvement of dairy and beef breeds, addressing all current problems in the field. This second edition includes a new team of authors and completely new chapters on the genetics of fat production, nutrition, feed intake and efficiency, growth and body composition. Fully updated throughout, it provides a valuable resource on cattle genetics for researchers, breeders, veterinarians and postgraduate students.

Vols. for 1963- include as pt. 2 of the Jan. issue: Medical subject headings.