H. de Rochambeau

Effects of divergent selection for body weight at a fixed age on histological, chemical and rheological characteristics of rabbit muscles

Abstract The aim of this study was to investigate the main carcass traits, and some of the histological, chemical and rheological characteristics of two muscles in two lines of rabbits divergently selected for body weight at 63 days of age. At slaughter, live body weight (+13%) and weights of semitendinosus (ST) and longissimus lumborum (LL) muscles (+13 and +8%, respectively) were heavier in the heavy line (HW) than in the light line (LW). At the same time, mean cross-sectional area of constituent myofibers was 6% larger in ST muscle from HW compared to LW lines; however, the number of myofibers remained steady in both lines. Shear force value was increased by 20 and 8% in ST and LL muscles, respectively, in HW compared to LW lines. Ultimate pH values in both muscles were similar for both lines. No effect of selection was denoted for intra-muscular fat content of ST muscles. This study suggests that selection for live body weight at a fixed age of slaughter affected muscle weight by myofiber hypertrophy and caused slight modifications of rheological properties of the muscles.

Factors affecting fleece traits of Angora goat in Argentina

Information collected over a fifteen-year period on an experimental flock were analyzed to evaluate the effect of year, age of dam, sex, and type of birth on the characteristics of the fleece at first shearing and the effects of year, age at shearing, and sex on the characteristics of the fleece at subsequent shearings. The variables analyzed were greasy fleece weight (GFW), average fiber diameter (AFD), percentage of medullated fibers (MF) and corrected greasy fleece weight (CGFW). At first shearing significant statistical differences were detected (P<0.05) for year, dams age, sex, and type of birth for GFW and CGFW. For AFD and MF, solely the shearing year was significant (P<0.05). Data collected from the second and following shearings showed differences (P<0.05) due to year of production, age at shearing time, and sex for the four variables analyzed. GFW increases to a maximum at 3–4 years of age, while CGFW is practically constant between 2 to 4 years of age, thus suggesting that the increase in fleece weight is due to an increase of AFD. On the other hand, MF shows a positive tendency related to age, for the analyzed interval of ages. In general, assuming comparisons are conducted within years of production, the results showed the importance of adjusting for age of dam, sex and type of birth for fleece weight, for traits collected at 12 months of age. For traits recorded at the second and later shearings adjustment for sex and age effects would be necessary for fleece weight, fiber diameter and log-transformed percent medullation. This result indicated, that to improve the estimation of breeding values in a selection scheme, it is necessary to use different models to adjust the data according to the yearly sequence of shearings.

Predicting the genetic drift in small populations

Abstract Predicting the genetic drift in small populations is considered over a short interval of time. A detailed description of the dynamic and spatial structure of the population is used, together with several measures of the change of genetic variability with time: mean inbreeding and kinship coefficients within and between groups of animals; percentages of genes contributed by the various foundation groups that made up the initial population; rate of loss of founder genes; joint distribution and random fluctuations of allelic frequencies. This approach is illustrated by means of two theoretical populations that model actual cattle breeds, and is applied to two problems: the conservation of a small population with or without freezing of semen, and the conflict between diffusion of genetic progress and random drift in a selected population conducted with or without superovulation and embryo transfer. Two main conclusions were drawn from these examples: 1. (a) Drift should not be characterized by single values (genetic effective size, or mean inbreeding coefficients), but rather by a set of criteria that have differentiated sensitivities to variations in demographic structure, mating scheme and gene diffusion. 2. (b) Quite large random variations in gene frequencies can be promoted by selection in seemingly large populations.

Angora rabbit wool production: non-genetic factors affecting quantity and quality of wool

A study was made of the wool production of 490 females and 137 males of a strain of French Angora rabbit. The female adults weighed 4107 g and produced 249 g of wool every 14 weeks. Production was low for the first harvest (35 g) which consisted mainly of short wool. It then increased rapidly (203 g for the third harvest). After the third harvest, three-quarters of long wool was also bristly. The length of bristles (102 mm) decreased by 4 mm, and that of downs (62 mm) increased by 3 mm when the harvest number went from two to four. The coefficient of correlation between wool production and live weight was lower than 0·30. Adult females born in autumn produced 16 g more than those born in summer. Wool production was at a maximum during autumn and winter harvests and at a minimum in summer. Winter fleeces had longer bristles and down than summer ones. Males produced well wool than females. When a female dropped a litter, her wool production decreases by proportionately 0·1 to 0·2. Bristly fleeces were clearly different from woolly fleeces on account of higher weight, homogeneity and compression. Objective criteria to evaluate tautness will have to found.

The inheritance of wool quantity and live weight in the French Angora rabbit

More accurate definition of Angora rabbit breeding objectives has been investigated by considering multiple expression of different traits. Data on 9672 fleece harvests produced by 1343 Angora does which had at least one wool harvest were analysed in order to study genetic variability according to age. The animals of the French breed were defleeced and weighed at 8 and 21 weeks of age for the first and second time respectively. Thereafter, does were defleeced every 14 weeks and weighed 9 weeks before defleecing. Total fleece weight and live body weight were recorded at each harvest. Direct heritability estimates of total fleece weight were similar accross ages and ranged from 0·31 to 0·42 . A significant maternal heritability was also observed at all ages of harvest. Maternal genetic estimates decreased with age from 0·44 at the first harvest to 0·10 for an adult harvest. Except for 8 weeks of age, genetic correlations between total fleece weight and live weight were generally not significantly different from zero. Genetic correlations of total fleece weight between the first and subsequent harvests were low (from 0·22 to 0·39) but genetic correlation estimates between consecutive harvests after the first were high, and ranged from 0·68 to 0·89 . The results suggest that the second harvest would be the first good predictor of breeding value for total fleece weight in the adult Angora rabbit.

Genetic description of a divergent selection experiment in Angora rabbits with overlapping generations

The chief aims of this paper were the following: (i) to describe the demography and genetic structure in two divergent selected lines for total fleece weight (TFW) of French Angora rabbits with overlapping generations; (ii) to describe the effects of inbreeding during an experiment of divergent selection. A study of longevity with the survival kit showed that there was no significant difference in the risk of death or culling between the low line (LL) and high line (HL). A significant effect of inbreeding (p < 0.05) was observed with a 30% higher risk factor in the highest class of inbreeding coefficient compared with the other classes. The means of generation interval were 562 and 601 days in LL and HL, respectively. The numbers of generations for LL and HL were 3.90 and 3.64, respectively. Generation intervals decreased significantly from 1995 to 2000 (p < 0.05). The number of daughters in HL was very variable. The number of animals per generation was higher in HL than in LL. Each buck left nearly three daughters to the next generation (2.52 in LL, 3.24 in HL). In both lines, the effective number of ancestor genomes still present in the genetic pool of the generation was around eight from the reference population of 1995 to that of 2001. Inbreeding in HL was always higher than in LL. The effect of inbreeding was also significant (p < 0.05) on TFW and live weight. The animals with the lowest inbreeding category produced a higher TFW (p < 0.05) than the others. The observed selection differentials were lower than that expected owing to the breeding animal management rules in order to control inbreeding increase.