Effects of floor type, stocking density, slaughter age and gender on productive and qualitative traits of rabbits reared in collective pens.

At 34 days of age, 376 crossbred rabbits of both sexes were housed in 16 open-top collective pens (1.68 m2) according to a 2×2×2 factorial arrangement with two types of pen floor (plastic v. wooden slatted), two stocking densities (12 v. 16 animals/m2) and two slaughter ages (76 v. 83 days). The rabbits were examined for growth performance, slaughter results and meat quality. The effect of gender was also examined. The percentage of rabbits with wounds due to aggression varied with stocking density (8.2% v. 26.2% for 12 v. 16 animals/m2; P⩽0.001), slaughter age (15.0% v. 22.0% at 76 v. 83 days; P⩽0.10) and gender (11.3% v. 25.8% for females v. males; P⩽0.001). Rearing rabbits on a plastic rather than a wooden slatted floor promoted slaughter weight (2795 v. 2567 g; P⩽0.001), dressing percentage (61.4% v. 60.9%; P⩽0.01), dissectible fat (2.4% v. 2.0%; P⩽0.01) and hind leg muscle-to-bone ratio (5.81 v. 5.35; P⩽0.001). Increased stocking density impaired daily growth (38.5 v. 35.9 g/day; P⩽0.05) and feed intake (140 v. 134 g/day; P⩽0.01) during the second period (55 days to slaughter) and decreased slaughter weight (2725 v. 2637 g; P⩽0.01). At the older slaughter age, the feed conversion ratio was impaired (2.98 v. 3.18; P⩽0.001); the slaughter weight (2574 g v. 2788 g; P⩽0.001), dissectible fat (2.0% v. 2.4%; P⩽0.01) and hind leg muscle-to-bone ratio (5.41 v. 5.75; P⩽0.01) increased; meat thawing losses, cooking losses and shear force decreased (P⩽0.05). The main differences between the females and males were found in the slaughter for transport losses (2.6% v. 2.2%; P⩽0.01) and longissimus lumborum proportions (13.0% v. 12.4%; P⩽0.01). In conclusion, the growth performance of pen-housed rabbits was largely determined by the type of floor and less affected by stocking density. The meat quality depended on ontogenetic factors, such as slaughter age and gender, and not on housing conditions. The differences in the percentages of wounded animals owing to experimental factors deserve further investigation from the perspective of animal welfare issues.

Housing of growing rabbits in individual, bicellular and collective cages: growth performance, carcass traits and meat quality.

During growth (from 27 to 75 days of age), 384 rabbits were kept in different types of wire-net cages: 72 individual cages (72 rabbits; 10 animals/m2), 48 bicellular cages (96 rabbits; 2 rabbits/cage; 18 animals/m2) and 24 collective cages (216 rabbits; 9 rabbits/cage; 18 animals/m2). The rabbits housed in individual cages showed higher daily weight gain both during the fattening period (from 52 to 75 days of age) and during the whole period of growth (43.0 v. 41.8 and 41.5 g/day; P < 0.05), and they had a higher final live weight at 75 days of age (2678 v. 2619 and 2602 g; P < 0.05) compared with the rabbits in the bicellular and collective cages, respectively. Rabbits in individual cages ingested more feed (133 v. 127 and 126 g/day; P < 0.01), but the feed conversion did not differ significantly among rabbits housed in the three types of cages. At slaughter, the carcass traits and meat quality were weakly affected by the housing system. The transport losses were higher in rabbits kept in individual and bicellular cages compared with those reared in collective cages (3.1% and 2.9% v. 2.2%; P < 0.01). In rabbits kept in individual cages, the hind leg muscle to bone ratio was higher (6.35 v. 6.19 and 5.91; P < 0.05) compared with the bicellular and collective cages, respectively. The pH and colour of the longissimus lumborum did not change with the housing system, while the b* index of the biceps femoris was lower (3.04 and 3.32 v. 4.26; P < 0.001) in the rabbits kept in individual and bicellular cages, respectively, than in those kept in collective cages. In conclusion, the rabbits housed in individual cages showed higher daily growth than rabbits kept in bicellular or collective cages, but they had a similar feed conversion and carcass quality. Differently, neither in vivo performance nor slaughter results differed among the rabbits kept in bicellular cages or in collective cages. The meat colour may be affected by the housing system, but to an extent that is hardly perceivable by the final consumer.

Housing of growing rabbits in individual, bicellular and collective cages: fear level and behavioural patterns.

During growth (27 to 75 days of age), a total of 384 rabbits were kept in 72 individual cages, 48 bicellular cages (2 rabbits/cage) and 24 collective cages (9 rabbits/cage). To evaluate the effects of the housing system on the fear level and behavioural patterns of rabbits at the two ages (39 to 45 days and 66 to 73 days), a tonic immobility test and an open-field test were conducted and their behaviour was video recorded. In the tonic immobility test, the number of attempts to induce immobility (1.38) was lower, and the duration of immobility (47.8 s) was higher (0.05 < P < 0.01) in the rabbits housed in individual cages than in those kept in bicellular (1.72 attempts and 25.0 s of immobility) and collective cages (1.99 attempts and 25.0 s of immobility). During the open-field test, the rabbits from individual and bicellular cages showed higher latency (38.8 and 40.3 v. 27.0 s), a lower number of total (73.3 and 81.7 v. 91.9) and central displacements (3.6 and 2.8 v. 5.4) and a shorter running time (11.8 and 13.6 s v. 17.7 s) and the time biting the pen (5.5 and 9.1 s v. 28.2 s) compared with the rabbits kept in collective cages (0.05 < P < 0.001). During the 24-h video recording, the rabbits in individual and bicellular cages spent less time allogrooming (0.34% and 0.19% v. 1.44%), moving (0.74% and 0.60% v. 1.32%) and running (0.08% and 0.03% v. 0.21%) than the rabbits in the collective cages (0.01 < P < 0.001). The lowest numbers of alerts and hops were observed in the rabbits kept in bicellular cages. With increasing age, a lower number of rabbits were sensitive to the immobility test and more rabbits entered the pen spontaneously during the open-field test (P < 0.001). In conclusion, the rabbits in individual cages exhibited the highest fear level and incomplete behavioural patterns; the rabbits housed in collective cages showed the lowest fear levels and had the possibility of expressing a wider range of behaviour; and the rabbits in bicellular cages exhibited an inconsistent pattern of fear in the tonic immobility and open-field tests. Probably, these rabbits were in a less stressful condition compared with animals in individual cages because social contacts were allowed, even if freedom of movement was more limited.

Effect of decreasing dietary protein level and replacing starch with soluble fibre on digestive physiology and performance of growing rabbits.

At weaning (33 days of age), 246 hybrid rabbits (782 ± 53 g live weight) were divided into six experimental groups and fed ad libitum six iso-ADF diets formulated according to a bifactorial arrangement with two protein levels (152 and 162 g/kg) and three soluble fibre-to-starch ratios (0.2, 0.6 and 1.5), the latter obtained by replacing starch (from 209 to 91 g/kg) with soluble fibre (from 48 to 136 g/kg). The trial lasted for 42 days until slaughter. The rabbits that were fed the diet with the highest protein level and the lowest soluble fibre-to-starch ratio showed the highest mortality rate (17.1% v. 1.7% on average; P < 0.001) and sanitary risk (mortality + morbidity: 20.0% v. 8.1%; P = 0.04) compared with the rabbits fed the other diets. With increasing dietary crude protein level, the digestibility of dry matter (DM; 0.615 to 0.626) and gross energy (0.620 to 0.630) as well as aNDF (without sodium sulphite; 0.298 to 0.323) and hemicelluloses (0.417 to 0.461) significantly (0.001 < P < 0.10) improved. Moreover, total volatile fatty acids (VFAs) in the caecal content increased (59.0 to 68.4 mmol/l; P = 0.01) and ileum crypt depth tended to reduce (P = 0.07). Neither growth performance nor slaughter results were affected by the protein level. When increasing soluble fibre-to-starch ratio, the digestibility of DM and gross energy did not change, whereas the digestibility of aNDF (0.264 to 0.352), ADF (0.167 to 0.267) and hemicelluloses (0.400 to 0.470) linearly increased (P < 0.001). At caecum, N-ammonia tended to decrease linearly (P = 0.08), total VFA concentration (56.0 to 67.3 mmol/l) and acetate proportion (80.4 to 83.3 mmol/100 mmol VFA) linearly increased (P < 0.01), whereas butyrate and valerate proportions decreased (0.01 < P < 0.05). Growth performance was similar among groups, whereas at slaughter the proportion of the gastrointestinal tract linearly increased (177 to 184 g/kg; P < 0.01) without effect on dressing percentage, however. As soluble fibre-to-starch ratio increased, meat pH linearly decreased and lightness (L*), redness (a*) and yellowness (b*) colour indexes increased (0.01 < P < 0.05).

Genetic heterogeneity at the bovine KIT gene in cattle breeds carrying different putative alleles at the spotting locus.

According to classical genetic studies, piebaldism in cattle is largely influenced by the allelic series at the spotting locus (S), which includes the S(H) (Hereford pattern), S(+) (non-spotted) and s (spotted) alleles. The S locus was mapped on bovine chromosome 6 in the region containing the KIT gene. We investigated the KIT gene, analysing its variability and haplotype distribution in cattle of three breeds (Angus, Hereford and Holstein) with different putative alleles (S(+), S(H) and s respectively) at the S locus. Resequencing of a whole of 0.485 Mb revealed 111 polymorphisms. The global nucleotide diversity was 0.087%. Tajima's D-values were negative for all breeds, indicating putative directional selection. Of the 28 inferred haplotypes, only five were observed in the Hereford breed, in which one was the most frequent. Coalescent simulation showed that it is highly unlikely (P < 10E-6) to obtain this low number of haplotypes conditionally on the observed number of segregating SNPs. Therefore, the neutral model could be rejected for the Hereford breed, suggesting that a selection sweep occurred at the KIT locus. Twelve haplotypes were inferred in Holstein and Angus. For these two breeds, the neutral model could not be rejected. High heterogeneity of the KIT gene was confirmed from a phylogenetic analysis. Our results suggest a role of the KIT gene in determining the S(H) allele(s) in the Hereford, but no evidence of selective sweep was obtained in Holstein, suggesting that complex mechanisms (or other genes) might be the cause of the spotted phenotype in this breed.

Investigation of candidate genes for glycolytic potential of porcine skeletal muscle: Association with meat quality and production traits in Italian Large White pigs.

The objective of this study was to investigate the association of DNA markers in candidate genes for glycolytic potential on meat quality parameters (pH(1), pH(u), glycogen and lactate content and glycolytic potential of semimembranosus muscle) and estimated breeding values (EBVs) for average daily gain, lean cuts, back fat thickness, ham weight, and feed:gain ratio in 272 Italian Large White pigs. Three mutations in the PRKAG3 gene (T30N, G52S and I199V) were investigated as well as single nucleotide polymorphisms in two other skeletal muscle genes (PGAM2 and PKM2) involved in the glycolytic pathway. Association analysis with the PRKAG3 markers showed significant results (P<0.05) only for pH(1) (I199V, with significant additive effect) and lactate content (T30N), confirming, at least in part, the effects of this gene on meat quality traits. Significant association (P<0.05) was also observed for PGAM2 and ham weight EBV with significant additive and dominance effects. PKM2 was associated with average daily gain, lean cuts (P<0.001), back fat thickness and feed:gain ratio (P<0.05), with significant additive and/or dominance effects on these traits. PKM2 encodes for a key enzyme of the muscle glycolytic pathway and maps on porcine chromosome 7 where other studies have reported important QTL for the same traits. These data might suggest an important function of this gene in the mechanisms that produce the observed effects. The results will be important to evaluate the inclusion of some of these DNA polymorphisms in marker assisted selection programs.

Mutations in the melanocortin 1 receptor (MC1R) gene are associated with coat colours in the domestic rabbit (Oryctolagus cuniculus).

We sequenced almost the complete coding region of the MC1R gene in several domestic rabbits (Oryctolagus cuniculus) and identified four alleles: two wild-type alleles differing by two synonymous single nucleotide polymorphisms (c.333A>G;c.555T>C), one allele with a 30-nucleotide in-frame deletion (c.304_333del30) and one allele with a 6-nucleotide in-frame deletion (c.280_285del6). A polymerase chain reaction-based protocol was used to distinguish the wild-type alleles from the other two alleles in 263 rabbits belonging to 37 breeds or strains. All red/fawn/yellow rabbits were homozygous for the c.304_333del30 allele. This allele represents the recessive e allele at the extension locus identified through pioneering genetic studies in this species. All Californian, Checkered, Giant White and New Zealand White rabbits were homozygous for allele c.280_285del6, which was also observed in the heterozygous condition in a few other breeds. Black coat colour is part of the standard colour in Californian and Checkered breeds, in contrast to the two albino breeds, Giant White and New Zealand White. Following the nomenclature established for the rabbit extension locus, the c.280_285del6 allele, which is dominant over c.304_333del30, may be allele E(D) or allele E(S).