A. Blasco

Mixed model methodology for the estimation of genetic response to selection in litter size of rabbits

Abstract Mixed model methodology was applied to estimate genetic trend of three rabbit strains (A, V and B) since there was no control line available. Strains A and V were selected on litter size at weaning by a selection index combining records on the doe, her mother, full sibs and half sibs. Strain B was selected on individual growth rate between 28 and 77 days. All strains were reared under the same conditions. Predictors of genetic values of litter size were obtained by using a repeatability model which included year-season of parity and reproductive state of the female (primiparous; lactating; non primiparous non lactating) as fixed effects. Variance components used to predict genetic value were estimated by using a large amount of data before selection. All relatives were considered when computing the relationship matrix. Genetic trend was estimated by regression of generation average of genetic predictors on generation number. Genetic trends were 0.05 ± 0.01 and 0.03 ± 0.02 weaned rabbits per generation for Strains A (7 generations) and B (6 generations) respectively. Genetic gain in Strain V was 0.16 weaned rabbits after 1 generation of selection.

A Bayesian analysis of the effect of selection for growth rate on growth curves in rabbits

Gompertz growth curves were fitted to the data of 137 rabbits from control (C) and selected (S) lines. The animals came from a synthetic rabbit line selected for an increased growth rate. The embryos from generations 3 and 4 were frozen and thawed to be contemporary of rabbits born in generation 10. Group C was the offspring of generations 3 and 4, and group S was the contemporary offspring of generation 10. The animals were weighed individually twice a week during the first four weeks of life, and once a week thereafter, until 20 weeks of age. Subsequently, the males were weighed weekly until 40 weeks of age. The random samples of the posterior distributions of the growth curve parameters were drawn by using Markov Chain Monte Carlo (MCMC) methods. As a consequence of selection, the selected animals were heavier than the C animals throughout the entire growth curve. Adult body weight, estimated as a parameter of the Gompertz curve, was 7% higher in the selected line. The other parameters of the Gompertz curve were scarcely affected by selection. When selected and control growth curves are represented in a metabolic scale, all differences disappear.

CARCASS CHARACTERISTICS AND MEAT QUALITY OF RABBIT LINES SELECTED FOR DIFFERENT OBJECTIVES : I. BETWEEN LINES COMPARISON

Abstract Rabbits from three lines (A, V, R), selected for different objectives, were slaughtered at three different liveweights (1800, 2050 and 2300 g). Lines A and V were selected for litter size at weaning, whereas line R was selected for growth rate between the 4th and 9th week of life. Fifteen animals of each of the nine combinations body weight group×line were used in the experiment. The composition of their carcasses as well as some of the characteristics of their meat were then compared. Dressing out percentage was between 51.48 of line R and 55.67 of line V. The thoracic cage was relatively more developed in lighter animals, they had less fat (0.8%) and had a smaller meat-to-bone ratio (4.16 v 4.87). The meat of the R line animals presented a higher pH, had less fat and loosed more water (40%) when cooked than the meat of line V (37.7%). We found significantly lower initial yield force (4.71) and maximum shear force (4.75) in line A in relation to the other two lines, being the line V (initial yield force=5.10 and maximum shear force=5.11) more close to line R (5.20 and 5.25, respectively). These results indicate a more tender meat in line A than in the other two lines. We can conclude that differences in tenderness in loin meat rabbit are more affected by genetic origin than by body weight. Females had more adipose tissue (4.07%) than males (3.65%). Female meat had a slightly more acid pH and retained more water.

The genetics of prenatal survival of pigs and rabbits: a review

Abstract Current knowledge on the genetic variability of prenatal survival (PS) in pigs and rabbits is reviewed. There is a large amount of variation between lines or breeds and these differences are not always negatively correlated with ovulation rate (OR); a line with a high OR can also have a high level of PS (e.g. the Meishan pig). Crossbreeding studies show that the maternal genotype is much more important in the control of line differences in PS than the the embryo/fetus, particularly the former, enhances PS, demonstrating the importance of non-additive genetic variation in the control of this trait. Only few estimates of the within breed genetic parameters of PS are available in the literature. Heritability seems to be low, with estimates ranging from 0 to 0.23. PS is negatively correlated with OR and positively correlated with number of embryos/fetuses (NE) or litter size (LS), but estimates of genetic correlations differ widely between studies. Selection for OR generally leads to an increase of NE at mid-gestation, but not at birth. Selection on a linear index combining OR and PS has not proved to be more efficient than selection on LS. New methods, such as unilateral hysterectomy/ovariectomy, which increases the emphasis on fetal survival and aims to measure uterine capacity, are currently under study and seem to be promising.

Carcass characteristics and meat quality of rabbit lines selected for different objectives

Abstract Rabbits from three lines (A, V and R) and three different weights (1800, 2050, 2300 g) were used in the experiment. Nine animals of each line and weight were used. Lines A and V were selected for litter size at weaning, whereas line R was selected for growth rate between the 4th and 9th week of life. Muscular pH of Longissimus (pHLD) at the level of the 5th lumbar vertebra and pH of Biceps femoris (pHBF) were taken 24 h post-mortem. Colour (L* lightness, C* chroma, H* hue) was measured on the carcass surface of the Longissimus muscle at the level of the 4th lumbar vertebra and at the 7th lumbar vertebra cut. Fat and moisture were estimated on fore leg muscles (including insertion and thoracic muscles), hind leg, abdominal wall and Longissimus muscle. Water holding capacity, cooking loss (CL) and texture (shear force) were estimated on Longissimus muscle. A principal component analysis was performed in order to examine the relationships between the traits measured. The four 1st PC explained a 63% of the total variation (29%, 16%, 10% and 8%, respectively). The principal component analysis showed that meat quality traits were grouped in independent sets. Fat-moisture, texture, pH and luminosity of Longissimus explained a large part of the observed variation. The differences between lines or liveweight groups in meat quality tend to be small, which implies a certain constancy in rabbit meat quality.

Carcass Composition and Meat Characteristics of Two Rabbit Breeds of Different Degrees of Maturity

Carcass and meat characteristics of rabbits from two synthetic breeds of different size were compared. Breed R had a higher adult weight and reached slaughter weight 1 week before breed V. Sixty rabbits of each breed were slaughtered when they (approximately) reached the Spanish commercial liveweight of 2 kg in order to compare their carcasses and meat quality. The carcasses were measured and retailed according to the norms of the World Rabbit Scientific Association. Breed R had a considerably more developed liver, a less developed hind part, and a more developed thoracic cage. Dissectible fat content was 3.1% and 2.5% of the carcass weight for the breeds V and R, respectively. Meat content was higher in the V breed than in the R breed (53 and 51% with respect to the chilled carcases). The ratio meat bone was better for breed V (2.18 and 2.05, respectively). Muscular fat content, estimated in the meat of one side of the carcass, was higher for breed V. All these differences are related to the lower degree of maturity of breed R at equal weights. Muscular pH, measured on the B. femoris and on the M. Longissimus lumborum at the level of the 5th lumbar vertebra, was the same for both breeds. Colour was measured on the carcass surface and in cuts of the M. Longissimus lumborum. Some colour differences were found for the carcass surface, but not for the meat.

Comparison of five types of pig crosses. II. fresh meat quality and sensory characteristics of dry cured ham

Abstract Carcasses of 109 gilts and 119 barrows from crosses including Duroc (DU), Landrace (LR), Large White (LW) and Belgian Landrace (BL) components were used to analyze their meat quality. The crosses were DU × (LR × LW), LW × (DU × LW), LW × (LR × LW), BL × (DU × LW), and BL × (LR × LW). Muscle pH and electrical conductivity were measured in the Longissimus dorsi (LD) and Semimembranosus muscles. Colour, water holding capacity, intramuscular lipid content, total protein and water content was determined on LD muscle. A sample of 32 right hams from each cross were dry-cured. The cushion (which includes the muscles Biceps femoris, Semimembranosus and Semitendinosus) was used for panel and consumer tests. There were no differences in meat quality traits related to PSE condition between DU and LW sired pigs, but BL sired pigs showed a poorer meat quality. Intramuscular fat content was higher in the DU sired pigs. Texture of hams produced by DU sired pigs and BL × (LR × LW were judged softer and more pastier. There were no significant differences between crosses in flavour characteristics. Consumer acceptability was better in LW and DU sired pigs. The DU dam genes in the BL sired pigs improved overall acceptability of the ham with respect to BL × (LR × LW), classified as the poorest ham.

Comparison of carcass and meat characteristics of three rabbit lines selected for litter size or growth rate

Rabbits from three synthetic lines were compared. Line V and A were selected for litter size at weaning and line R was selected for growth rate between weaning and slaughter time. Forty animals of each line were slaughtered at 9week of age. Comparisons between lines were made using Bayesian statistical techniques. Line R had a higher meat/bone ratio, higher loin percentage and higher ultimate pH of M. Longissimus lumborum (LL) than A and V, but lower dressing out and lower hind part percentages. Some differences between lines in carcass and meat colour were found. No differences were found for percentage of released water of LL and for the activity of energy metabolic enzymes. At present, rabbit carcasses are not costed according to their retail cuts or meat/bone ratio, but dressing out percentage is taken into account, thus breeding companies should be concerned about lower carcass yield of lines selected by growth rate.

The use of Bayesian statistics in meat quality analyses: a review.

A Bayesian approach to meat quality analyses is discussed and compared with the classical statistical approach. Inferences from means, medians and modes of marginal posterior distributions are presented, and a variety of probability inferences and confidence intervals are presented and discussed. Classical and Bayesian theories of hypothesis testing are compared and their advantages and disadvantages are discussed. Fundamentals of Bayesian inference and Monte-Carlo Markov Chain (MCMC) techniques are presented and discussed. The great flexibility for inferences introduced by MCMC techniques is stressed. Practical examples of meat quality analyses are given, with references to available free software to analyze a large variety of models.

Relationships between meat quality measurements in rabbits fed with three diets of different fat type and content.

Two hundred and eighty-four, genetically similar (a three-way cross), young rabbits were fed ad libitum, from weaning, either a commercial diet (group C, ether extract 2.6%) or a diet containing vegetable fat (group V, ether extract, 9.9%) or animal fat (group A, ether extract 11.7%). A principal component (PC) analysis was performed with the variables: ultimate pH at 24 h post mortem measured in the longissimus dorsi (LD) and in the biceps femoris (BF) muscles, colour measured on the surface of the loin, fatty acid composition of perirenal fat, meat fat content of the hind leg, water holding capacity and cooking losses of the meat, and sensory variables determined by a trained panel test. The four first PC explained 62% of the total variation (27, 13, 11 and 11%, respectively). The first PC grouped the fatty acids, the second PC grouped the sensorial variables, and the third and fourth PCs grouped the pHs and the water holding capacity. The projection of the data in the first two PCs showed three separate groups of points. Animals fed with diet V were on the left side of the graph, where the variable C18:2 lies, whereas animals fed with diets A and C lay on the right side of the graph, where the saturated acids were grouped. These were slightly separated by the higher content of oleic acid in the animals fed with diet A. The second PC, where the sensorial variables were grouped, did not separate the animals fed with diets A, V and C. The diets used in this experiment had only a slight influence on the organoleptic characteristics of rabbit meat.