M. Baselga

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.

Selection response of growth rate in rabbits for meat production.

Genetic and environmental trends in 2 lines of rabbit (B and R) selected on individual weight gain (WG) from weaning (4 wk) to slaughter (11 wk) were estimated using mixed model methodology. Line B was derived from the California breed and line R was a synthetic of stock of different origin. The data were collected from a single herd and comprised 7 718 individuals in line B and 9 391 in line R, the lines having 12 and 9 generations of selection respectively. Realized responses in the 2 lines were 2.7% and 2.2% of the initial mean per year respectively and showed that selection on WG was effective but was less than expected. Selection on slaughter weight (SW) and effects of selection on other economic traits are discussed. It is concluded that selection on either WG or SW is a simple method for improving growth rate in rabbit sire line stocks.

Estimation of genetic response to selection in litter size of rabbits using a cryopreserved control population

Abstract An analysis of the response to selection in a line of rabbits selected on litter size at weaning for 21 generations was carried out. The selection method was based on a BLUP procedure under a repeatability animal model. Embryos of generation 15 were vitrified in order to estimate the response to selection after thawing and transferring these embryos six generations later so that reproductive traits of females of generation 15 and 21 could be recorded at the same time. The direct response to selection between both generations was 0.51±0.25 rabbits weaned/litter (0.085 per generation), and there were correlated responses in total litter size at birth (0.62±0.28) and number of young rabbits born alive (0.57±0.28). Laparascopies were carried out at 12 days of the 2nd and 3rd pregnancy to record litter size components between ovulation and birth. There was a significant response in ovulation rate (1.08±0.62) that may be a main cause of the success in the selection process. Also, the genetic trends have been estimated using mixed model methodology, with all the information of the selection process (12 651 parities across 21 generations of selection), and the results agreed with the previous ones. Thus, the estimated genetic trend for litter size at weaning per generation was 0.09±0.003.

Effects of pig sire type and sex on carcass traits, meat quality and sensory quality of dry-cured ham

Five different sire types, Danish Duroc (DU), Dutch Large White (LWD), English Large White (LWE), Belgian Landrace × Landrace (BL × LR) and Belgian Landrace (BL), were mated with LR × LW crossbred sows. Their offspring were compared on carcass traits, meat quality measurements and sensory characteristics of dry-cured ham. An animal mixed model was used to analyse these traits. BL-sired pigs had the worst score for meat quality but the highest killing out proportion and the best carcass conformation, with a higher percentage of ham and shoulder. On the other hand, DU-sired pigs had a good score on meat quality measurements as well as low subcutaneous fat and a good carcass conformation. Sensory analysis of dry-cured ham revealed that the BL-sired pigs showed a high ‘rancid’ aroma, although this sire type presented a low ‘marbling’ appearance. Dry-cured ham from BL × LR-sired pigs was characterised by a high ‘fat complex’ aroma and a low level of ‘tyrosine crystals’, and from DU-sired pigs by high ‘marbling’ and ‘tyrosine crystals’ and a low aroma content. The females produced a higher percentage of ham and dry-cured ham with a higher ‘overall quality’ than the males. It can be concluded that the appropriate genetic type for dry-cured ham processing is the DU sire because of its high desirable ‘marbling’ descriptor. © 1999 Society of Chemical Industry

Effects of the terminal sire type and sex on pork muscle cathepsins (B, B+L and H), cysteine proteinase inhibitors and lipolytic enzyme activities

Pork muscle cathepsins (B, B+L, and H), cysteine proteinase inhibitors and lipolytic enzyme activities were measured in the offspring of five different genetic sire types: Danish Duroc (DU), Dutch Large White (LW(D)), English Large White (LW(E)), Belgian Landrace × Landrace (BL×LR) and Belgian Landrace (BL). Cathepsin B and B+L activities were higher for LW(E) and LW(D) sires than for BL×LR and BL. Cathepsin H activity showed an opposite evolution, being higher for BL and BL×LR sires than for DU, LW(D) and LW(E). Cysteine proteinase inhibitor activity was higher for LW(E) sires than for DU and BL. In lipolytic enzymes, BL sires had a lower acid lipase activity than DU and LW(E) sires and also a lower neutral esterase activity than LW(E) and LW(D) sires. Significant differences between sexes were found for cathepsin H activity only, being higher for females.

Comparison of growth and feed efficiency among rabbit lines selected for different objectives

Abstract An experiment has been carried out to evaluate correlated responses in feed efficiency in lines selected for postweaning daily gain and litter size, respectively. One sire line, selected for growth rate for 19 generations, and two dam lines, selected for litter size at weaning for 14 and 18 generations, have been compared for weaning weight (28 d), daily gain (28–63 d), feed intake and feed conversion. Large differences between the sire line and the dam lines are expected for the last three traits as a result of the different methods of selection. The most important estimated differences between lines during the postweaning growth period (weaning at 28 d, and slaughter at 63 d) were: The sire line grew about 9 g/d (24%) faster than the dam lines, had a greater feed consumption of 17 g/d (14%) and a lower feed conversion rate of 0.33 (11%). Selection of the sire line for growth rate is suggested as the main cause of the differences between the lines.

Estimation of correlated response on growth traits to selection in litter size of rabbits using a cryopreserved control population and genetic trends

Abstract An experiment is performed to contemporaneously compare young rabbits six generations apart in order to evaluate the correlated response to selection on growth traits in a line selected on litter size at weaning for 21 generations. The selection method was based on a BLUP procedure using a repeatability animal model. The contemporary comparison was possible because techniques of embryo cryopreservation and transfer were used in generation 15. The direct response to selection between both generations has been studied by Garcia and Baselga [Livest. Prod. Sci. 44 (2002) 45–53] and was 0.51±0.25 rabbits weaned/litter (0.085 per generation). In this paper, growth traits have been studied and the results show that non-significant differences between both generations were found, using as covariate total litter size at birth. Also, heritability, genetic correlations between growth traits and litter size at weaning, and genetic trends have been estimated using mixed model methodology with all the data of the selection process (12 651 parities and 93 085 growth records across 21 generations of selection). The genetic correlations were close to zero and the estimated genetic trend for weaning weight and post-weaning daily gain were positive and significant but small, less than 0.3% of the means per generation.

Late reproductive senescence in a rabbit line hyper selected for reproductive longevity, and its association with body reserves

The aim of the present study was to investigate differences in reproductive and body traits during successive parities between two genetic lines. The LP line was constituted by means of selection of animals having an extremely high number of parities (at least 25) and an average reproductive performance compared to the V line selected for litter size at weaning during 31 generations. The two lines were found to have an equal reproductive performance in the first three parities, but the LP line had higher reproductive performance from the fourth parturition onwards. The low reproductive performance after the third parity in the V line was suggested to be caused by constrained environmental conditions in the test station. A line by parity interaction was also observed for body weight, since body weight declined going from the third to the fourth parity in the LP line but not the V line. Thus, it was concluded that hyper selection for reproductive longevity and average prolificacy successfully delayed reproductive senescence, and that this newly founded line showed less environmental sensitivity, which might have been mediated by a higher body reserve.

Comparison of carcass characteristics in five strains of meat rabbit selected on different traits

Abstract Two experiments were conducted in order to compare carcass characteristics of five selected rabbit strains. Three of these lines are selected on litter size at weaning (Lines A, P and V, considered as dam lines), and the other two strains are selected on growth rate (lines C and R). Lines A, R and V were included in Experiment 1 (E1). Slaughter criterion was liveweight (around 2000 g). In Experiment 2 (E2) animals came from lines C, P, R and V, and they were processed at a fixed age (60 days). Line R reached the commercial liveweight a week before lines A and V in E1. In E2, liveweight of line R was higher than in line C (313 g), and than in lines V and P (510 and 508 g). Adjusting to a constant liveweight, in both experiments the gastrointestinal tract in line R was 11% heavier than the average of the others. As a result, dressing and dressing out percentages were lower. Dressing out percentages were over 57% in the other lines. Fat content (expressed as perirenal fat weight and adjusted to a constant reference carcass weight) of line R was the lowest in both experiments. In E1, line V (15.9 g) had the heaviest fat deposits and line A was intermediate (14.6 g). In E2, line C (23.3 g) had the highest perirenal fat weight, followed by dam lines (line V (20.5 g) and line P (19.9 g)). In E1 the lowest hind part weight (adjusted to a constant reference carcass weight) corresponded to line R and the highest to line V. In E2 this part was heavier in line V than in lines R and C. These results revealed that line R was less mature than the others at slaughter. When dam lines were compared for maturity at slaughter, only small differences were found in Experiment 1. Overall, the results showed that line R, selected on growth rate for twenty generations, showed the most important differences compared to the other lines. In E2, liveweight of line C was 10% higher than in lines V and P, and the fat content was the heaviest. Models of analyses including covariates had an excellent behaviour despite the wide range of values in E2.

Effects of sire type and sex on pork muscle exopeptidase activity, natural dipeptides and free amino acids

Five sire types, namely Danish Duroc (DU), Dutch Large White (LWD), English Large White (LWE), Belgian Landrace × Landrace (BL × LR) and Belgian Landrace (BL), were mated with LR × LW crossbred sows. Dipeptidylpeptidase and aminopeptidase activities and free amino acid and natural dipeptide contents were compared between the offspring of each sire type. Regarding the sire type effect, significant differences were detected in dipeptidylpeptidase I and IV and alanyl and pyroglutamyl aminopeptidase activities, with activity being lowest in the offspring of BL sires. Significant differences were also observed between sire types in the content of aspartic acid, glutamic acid, serine, glycine, glutamine, histidine and arginine. Taking into account the role of exopeptidases and free amino acids in taste development, the meat from BL-sired pigs may be considered as inferior in generating flavour precursors and thus not appropriate to undergo a dry-curing process. © 1999 Society of Chemical Industry