Abstract
BackgroundMost rabbit production farms apply feed restriction at fattening because of its protective effect against digestive diseases that affect growing rabbits. However, it leads to competitive behaviour between cage mates, which is not observed when animals are fed ad libitum. Our aim was to estimate the contribution of direct (d) and social (s) genetic effects (also known as indirect genetic effects) to total heritable variance of average daily gain ({text{ADG}}) in rabbits on different feeding regimens (FR), and the magnitude of the interaction between genotype and FR (G × FR).MethodsA total of 6264 contemporary kits were housed in cages of eight individuals and raised on full (F) or restricted (R) feeding to 75% of the ad libitum intake. A Bayesian analysis of weekly records of {text{ADG}} (from 32 to 60 days of age) in rabbits on F and R was performed with a two-trait model including d and s.ResultsThe ratio between total heritable variance and phenotypic variance (T^{2}) was low (<0.10) and did not differ significantly between FR. However, the ratio between h^{2} (i.e. variance of d relative to phenotypic variance) and T^{2} was ~0.52 and 0.86 for animals on R and F, respectively, thus s contributed more to the heritable variance of animals on R than on F. Feeding regimen also affected the sign and magnitude of the correlation between d and s, i.e. −0.5 and ~0 for animals on R and F, respectively. The posterior mean (posterior sd) of the correlation between estimated total breeding values (ETBV) of animals on R and F was 0.26 (0.20), indicating very strong G × FR interactions. The correlations between d and s in rabbits on F and R ranged from −0.47 (d on F and s on R) to 0.64.ConclusionsOur results suggest that selection of rabbits for {text{ADG}} under F may completely fail to improve {text{ADG}} in rabbits on R. Social genetic effects contribute substantially to ETBV of rabbits on R but not on F. Selection for {text{ADG}} should be performed under production conditions regarding the FR, by accounting for s if the amount of food is limited.
Highlights
Most rabbit production farms apply feed restriction at fattening because of its protective effect against digestive diseases that affect growing rabbits
They did not find any effect of feed restriction on the coefficient of variation in body weight, which could indicate that, in spite of the competition, all kits faced the same level of feed restriction [5]
Phenotypic analysis of body weight (BW) and average daily gain (ADG) In this experiment, we confirmed that feed restriction has a protective effect on the health of growing rabbits with the mortality rate being 14.6% for animals on F and 9.5% for animals on R
Summary
Most rabbit production farms apply feed restriction at fattening because of its protective effect against digestive diseases that affect growing rabbits It leads to competitive behaviour between cage mates, which is not observed when animals are fed ad libitum. Piles et al Genet Sel Evol (2017) 49:58 reported This interaction effect could be relevant when animals are bred in collective cages, which is the most common practice on commercial rabbit farms and elicits competition for feed intake between cage mates. By restricting the amount of food to 75% of the ad libitum intake and providing it once a day, Dalmau et al [4] observed that signs of antagonistic behaviour such as biting, displacement and animals jumping one on top of each other occurred during the whole growing period They did not find any effect of feed restriction on the coefficient of variation in body weight, which could indicate that, in spite of the competition, all kits faced the same level of feed restriction [5]
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