An exceptional muscle development commonly referred to as 'double-muscled' (Fig. 1) has been seen in several cattle breeds and has attracted considerable attention from beef producers. Double-muscled animals are characterized by an increase in muscle mass of about 20%, due to general skeletal-muscle hyperplasia-that is, an increase in the number of muscle fibers rather than in their individual diameter. Although the hereditary nature of the double-muscled condition was recognized early on, the precise mode of inheritance has remained controversial; monogenic (domainant and recessive), oligogenic and polygenic models have been proposed. In the Belgian Blue cattle breed (BBCB), segregation analysis performed both in experimental crosses and in the outbred population suggested an autosomal recessive inheritance. This was confirmed when the muscular hypertrophy (mh) locus was mapped 3.1 cM from microsatellite TGLA44 on the centromeric end of bovine chromosome 2 (ref. 5). We used a positional candidate approach to demonstrate that a mutation in bovine MSTN, which encodes myostatin, a member of the TGF beta superfamily, is responsible for the double-muscled phenotype. We report an 11-bp deletion in the coding sequence for the bioactive carboxy-terminal domain of the protein causing the muscular hypertrophy observed in Belgian Blue cattle.

We have determined the entire myostatin coding sequence for 32 double-muscled cattle sampled from ten European cattle breeds. Seven DNA sequence polymorphisms were identified, of which five would be predicted to disrupt the function of the protein, one is a conservative amino acid substitution, and one a silent DNA sequence variant. Four additional DNA sequence polymorphisms were identified in myostatin intronic sequences. In all but two breeds, all double-muscled animals were either homozygous or compound heterozygotes for one of the five loss-of-function mutations. The absence of obvious loss-of-function mutations in the coding sequence of the two remaining breeds points either towards additional mutations in unexplored segments of the gene, or towards locus heterogeneity of double-muscling.

No abstract

Docility tests were performed over 3 trait with four classes. Tests were performed by seven yr on 906 Limousin heifers sired by 34 males. The different handlers. The effects of handler, year, birth heifers were tested individually when they were 10 t o period, dam parity, birth region, husbandry system, 11 mo old in a pen with a handler who had 2 min to and sire were estimated. Handlers, birth period, lead the animal to a corner, keep it there for 30 husbandry system, and sire had significant effects. In consecutive seconds, and then to stroke it. Behaviors particular, animals that were managed indoors were of the animals were recorded and scores calculated. more docile than those reared out-of-doors at least The first score (docility score) was a continuous part of the time. Heritability estimates of the docility variable combining the greatest possible information. score ( .2 2) and docility criterion ( .l 8 ) seem sufficientThe second score (docility criterion) was a categorical to select for docility traits.