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In this study we resequenced 1729 bp of the rabbit melanocortin 4 receptor (MC4 R) gene in 31 rabbits from different breeds/lines and identified ten polymorphisms: one was an indel and 9 were single nucleotide polymorphisms (SNPs). The indel and 5 SNPs were in the 5'-flanking region, 3 were synonymous SNPs and one was a missense mutation (c.101G>A; p.G34D), located in a conserved position of the extracellular tail of the MC4 R protein. The missense mutation was analyzed in a panel of 74 rabbits of different breeds and in 516 performance tested rabbits of a commercial paternal line under selection for growth efficiency. Association analysis indicated that rabbits with the less frequent genotype in this population (DD) had a lighter weight at 70 postnatal days than animals with genotype GD (P < 0.10) and animals with genotype GG (P < 0.05). This is the third study on candidate genes, after those on GH1 and IGF2 that reported a marker associated with finishing weight. Therefore, it seems that a candidate gene approach in rabbit based on previous information accumulated in other livestock species could be useful to identify genes explaining a fraction of variability of performance traits with potential application on rabbit breeding and selection.

In rabbits' reproductive performance, litter size, birth weight, growth, and mortality rate are among the most important indicators to define the productive potential and they are associated with parity order. Birth weight and little size are valuable parameters as related to mortality and weaning weight. Thus, it is important to study individual newborn and intra-litter homogeneity parameters. This trial aimed to consider the litter homogeneity weight at birth, both within each litter and in the whole population, in order to suggest new proper within-litter homogenisation parameters. In this study, the 1st and 6th parity order had, respectively, the lowest and highest values in litter size (8.96 vs 12.39, n), born-alive (8.36 vs 12.22, n), litter weight (456.4 g vs 719.8, g), born-alive weight, and quartiles' homogeneity. These parameters decreased in greater parity orders. No significant effects on stillborn numbers and mortality rates were evidenced. All these litter homogeneity evaluation parameters appeared interesting in describing differences between parity orders. The results confirmed that does parity order influences litter size and born-alive weight, but also the intra-and inter-litter homogenisation. Litter homogenisation is crucial to ensure a proportionate share of milk, more equal growth, and better productive performances. Based on these results, we suggest for the commercial genetic centres to equalise the litters according to the birth weight, by dividing the population into quartiles and rearing kits with light birth weight in smaller litters and those with heavier birth weight in larger litters. HIGHLIGHTS Does parity order influences litter size and born-alive weight Kit's quartiles distribution is a useful tool for equalisation practice

Runs of homozygosity (ROH) are defined as long stretches of DNA homozygous at each polymorphic position. The proportion of genome covered by ROH and their length are indicators of the level and origin of inbreeding. In this study, we analysed SNP chip datasets (obtained using the Axiom OrcunSNP Array) of a total of 702 rabbits from 12 fancy breeds and four meat breeds to identify ROH with different approaches and calculate several genomic inbreeding parameters.The highest average number of ROH per animal was detected in Belgian Hare (~150) and the lowest in Italian Silver (~106). The average length of ROH ranged from 4.001 ± 0.556 Mb in Italian White to 6.268 ± 1.355 Mb in Ermine. The same two breeds had the lowest (427.9 ± 86.4 Mb, Italian White) and the highest (921.3 ± 179.8 Mb, Ermine) average values of the sum of all ROH segments. More fancy breeds had a higher level of genomic inbreeding (as defined by ROH) than meat breeds. Several ROH islands contain genes involved in body size, body length, pigmentation processes, carcass traits, growth, and reproduction traits (e.