In a selection experiment, 317 Charolais young bulls, progeny of 58 sires divergently selected (2x29) on their own growth capacity and feed efficiency measured in performance testing stations, have been tested in an experimental herd. Carcass weight and composition have been measured as well as nine different biological characteristics of the Longissimus dor si muscle related to meat quality. The responses observed on the progeny show that the selection procedure applied in the performance testing stations is appropriate for improving the muscle growth capacity and does not change markedly the biological components of meat quality. These responses and the estimated genetic correlations show a tendency that higher muscle growth capacity is related to later physiological development Selecting leanner animals will certainly have favourable effects on tenderness (higher thermal solubility of the collagene and higher proportion of rapid-white type of fibers) and a reduction of intramuscular lipid content. As heritability coefficients of most of these muscle characteristics are high enough, they can eventually be used as selection criteria in breeding programmes to improve related meat qualities as long as they can be easily measured.

INTRODUCTION The interest of using double muscled bulls from beef breeds for terminal crossbreeding, due to the high beef value of their calves, was shown a long time ago (Bibé et al., 1974 ; Ménissier, 1982a). This is why in France, several selection programmes using double muscled bulls for terminal crossbreeding by artificial insemination (AI) was developed over several decades. The first programme is based on the recruitment or even the procreation in herds of young double muscled Charolais bulls that strongly express muscular hypertrophy. These bulls are then evaluated on the value of their progeny (expression of “very early muscling” at 1 month of age) crossbred with dairy cows. Two AI units are responsible for such programmes : UCEAR Midatest (CHAROLAIS EXCELLENCE Programme) and UCEF UCHAVE. The second programme is the selection of a double muscled male strain specialised in terminal crossbreeding (INRA95 ; Ménissier, 1982). This specialised strain began being created in 19671968 by INRA in partnership with an AI unit (Midatest). The selection of the herd strain and the procreation of males are done at the Carmaux experimental farm of INRA. This step as well as the production and the sale of semen are performed by Midatest. After the discovery that the different mutations of the myostatin gene are responsible for muscular hypertrophy (Grobet et al., 1998), and the development of a genotyping test for these mutations (Miranda et al., 2000 ; Miranda et al., 2002), we genotyped the calves of the INRA95 strain which were recently tested. The object of this paper was to evaluate the frequency of mutations resulting from selection and to estimate the effects of the mutations on the performance of young calves in the herd strain.

SummaryThe myostatin gene codes for a growth factor involved in muscle development, and polymorphism in this gene can have important economic consequences. Nine mutations affecting the amino‐acidic sequence have already been described, six of which are disruptive, inactivating the protein and causing bovine muscular hypertrophy. As the number of known mutations grows, it is necessary to develop a simple, routinely usable technique able to screen individuals in all populations. The oligonucleotide ligation assay (OLA) is proposed here for the rapid genotyping of the nine mutations known affecting the coding sequence in the main breeds of beef cattle. This technique showed its ability to reveal the genotype of individuals being a good tool to determine the frequency of each mutation in a population. The procedure is very flexible as new mutations can be added and removed at any time. Depending on the genotype of each individual, the technique allows breeders to make quick decisions on matings and general selection tendencies.

Data (n=1725) were collected from 613 primiparous and multiparous Charolais cows managed in an experimental herd over a 10-year period. The objectives of the study were to describe the variability in the re-establishment of postpartum reproductive activity. The duration of the postpartum anoestrus period was estimated from progesterone concentrations in weekly blood samples, and from daily detection of oestrous behaviour. Oestrous behaviour was first observed 71.9 days (±27.2 S.D.) post-calving, and a first positive progesterone concentration (≥1 ng/ml) was observed at 68.7 days (±25.5 S.D.). There were differences in the chronology of these events: a first positive progesterone test was detected before the first oestrus in 51% of the cases. The duration of the first oestrous (25.6±16.4 days) and ovarian (2.8±0.9 weeks) cycles varied according to the chronology of the events. Year and period of calving, calving difficulty and parity (interacting with suckling status) significantly affected the duration of the postpartum anoestrus period. These results also showed an important effect of individual female on the duration of postpartum anoestrus with a repeatability of 37% for the interval to the first oestrus and 60% for the interval to the first positive progesterone test.

The purpose of this work was to compare muscle fibre differentiation in two genetic types: "normal Charolais" and double-muscled (DM) "INRA 95" cattles displaying muscle hypertrophy. Six muscles with different contractile and metabolic characteristics in adult animal: Masseter, Diaphragma (Di), Biceps femoris (BF), Longissimus thoracis, Semitendinosus and Cutaneus trunci (CT) were excised from 60 to 260-day-old foetuses of both genotypes. These muscles present different degrees of hypertrophy in DM animals. Fibre types were characterised by immunohistochemistry using mon- oclonal antibodies raised against different myosin heavy chain isoforms. They were also studied by SDS-PAGE electrophoresis, immunoblotting and ELISA methods. In both genotypes, foetal muscle development involved at least two generations of fibres but their contractile differentiation was more or less delayed in double-muscled animals according to the muscle type. CT muscle, the most hyper- trophied in adults DM, showed the most important differences in the appearance of the primary and secondary fibres in DM foetuses. It showed a delay of differentiation which was made up during the last third of foetal life. Other muscles did not differ in the speed of appearance of the two gener- ations of fibres. They were originated from a higher proliferation of secondary fibres. Moreover, all DM muscles presented similar characteristics at 210 days of foetal life. These characteristics seem to be genetically determined. Just before birth, muscles of double-muscled foetuses were composed of a greater proportion of fast type II fibres than normal animals. The most important differences between genotypes were observed in BF and Di muscles. muscle / foetus / differentiation / cattle / double-muscled

The ontogenesis of total collagen and of different collagen types was studied in four muscle types from genetically different cattle. Hydroxyproline content was 1.2-fold higher in muscles from cross-bred foetuses with normal muscle growth compared to those of the other genetic types (pure bred with different growth rates, double-muscled breed). A similar tendency was observed for type III collagen content. In all muscles of each animal studied, type XII and XIV collagens were colocated in perimysium. Immunolabelling obtained for type XII collagen was higher during foetal life than after birth, while for type XIV collagen, the opposite result was obtained. Whatever the muscle studied, but especially in semitendinosus muscle, during the foetal and the post-natal period until 15 months of age, immunolabelling with antibody anti-type XIV collagen tended to be more intense in muscles of animals from fathers selected for a low muscle growth capacity compared to those from fathers selected for a high muscle growth capacity. In conclusion, this study shows, that during foetal life, selection according to muscle growth capacity has no significant effect on the contents of total hydroxyproline or type III collagen, but minor effects on collagen localization.

The genetic variability of age at puberty estimated by the age at the first observed oestrus and the age at the first positive progesterone test was described for 351 Charolais heifers, the progeny of 60 sires, The relationship between age at puberty and growth rate of the heifers was also studied. Estimates of heritability were 0.34 for the age at the first observed oestrus and 0.27 for the age at the first positive progesterone test. The genetic correlation between these two criteria was high (r(g) = 0.94). Negative environmental relations existed between age at puberty and growth rate of the heifers until 1 year of age and with mature weight. The genetic relationship between puberty criteria and growth rate was also negative. Heifers with a high genetic potential for growth also had a high potential for an early puberty. Puberty age criteria were, however, independent of the degree of weight maturity at 1 year of age but negatively related to adult weight. Weight maturity at the first oestrus was highly correlated (r(g) = 0.70) with age at the first oestrus. ((C) Elsevier / Inra).

In an experimental Charolais herd of 351 heifers, the establishment of puberty was described through 2 monthly blood progesterone assays at 10-day intervals and daily oestrus observations between 10 and 20 months of age. At 15 months of age, 72 % of the heifers exhibited an oestrous behaviour, 56 % a positive progesterone assay and 53 % the two events. The mean age and weight at the first oestrus were 426 +/- 42 days and 406 +/- 38 kg (respectively, 445 +/- 43 days and 418 +/- 36 kg at the first positive progesterone test). Environmental factors influencing age at puberty were identified: year and period of birth, age of dam and twinning birth. Some of these factors act through an effect on the growth rate of the heifer. When data were adjusted for these factors, a moderate favourable phenotypic relationship still existed between growth rate and puberty-related traits. ((C) Elsevier / Inra).

This paper presents a procedure for the development of a breeding objective for a beef cattle breed used in a range of production systems. The five main beef cattle production systems in France were first described and then equations of income and costs as a function of the 25 biological traits to be genetically improved for breeding and production were established. Economic values for individual systems were defined as the first derivative of the herd profit with respect to these 25 traits while the economic values for the overall breeding objective were taken as the average of economic values over the five production systems. An application is presented for the Limousin breed. Sensitivity of the breeding objective to variation in the economic or demographic context was also studied. Breeding traits, especially maternal effects on weaning weight and calving success, were identified as the most economically important traits requiring improvement. Relative economic values were very robust with respect to variations in system frequencies and replacement rates. A dramatic change in the market price for beef (−50%) increased the relative weighting of carcass quality traits to the detriment of breeding traits although a smaller change in beef price (−25%) had no significant effect on the relative economic values.

In an experimental Charolais herd, the recovery of sexual activity after calving is determined by means of a weekly blood progesterone assay and by a twice daily detection of heats from the forth week post-partum. This resumption of activity is affected by several factors, the most important of which are suckling, parity and calving difficulty (caesarean section vs natural parturition). Moreover the relationship between the duration of the post-partum anoestrus period and some production traits are studied. It appears that a low weight or a poor body condition at calving or a body weight loss after calving will lengthen the duration of the post-partum acyclic period especially in primiparous cows.

This paper describes the scheme developed by the French and the British Limousin societies to increase the genetic links between the two populations. It underlines the different necessary stages to obtain a formula conversion of the estimated breeding values:the knowledge for producing an evaluation system;the knowledge and the measurements of the genetic links across the countries;the schedule to develop enough genetic links (if necessary).