Feeding mulberry leaves to fattening rabbits: effects on growth, carcass characteristics and meat quality

Abstract

AbstractOne hundred and thirty-two young rabbits were divided into two groups at weaning and given ad libitum a control diet (C), or an experimental diet (M) in which lucerne hay was substituted by mulberry leaves in order to examine their effects on fattening rabbit performance, carcass characteristics and meat quality.Digestibility coefficients of dry matter (DM), crude protein and gross energy were similar in both groups but digestibility of crude fibre in the experimental diet was higher in line with a lower food intake in this group of animals, while ether extract digestibility of mulberry leaves was very low.Food conversion ratio was similar in the two groups (3.1 g DM per g gain) but rabbits given the experimental diet had lower food intake (102 v. 144 g/day) and impaired live-weight gain. The rate of mortality was similar in the two groups. The substitution of lucerne with mulberry in the diet may have induced a higher retention time of digesta, as seems to be indicated by a higher weight of digestive tract contents recorded at slaughter (proportionately 0.32 more) in mulberry group. Live weight at slaughter of animals in control group was higher (2680 v. 2211 g) and also skin weight was proportionately 0.5 higher and its carcasses were proportionately 0.41 heavier than those of animals in experimental group (dressing yield 587 v. 503 g/kg). At constant carcass weight, the carcasses of rabbits of the mulberry group were longer than the lucerne group, but lumbar circumference tended also to be higher (P = 0.09) and no differences were found in the length: circumference ratio. No differences were found in the weights of kidneys or thoracic viscera, but livers of rabbits of the lucerne group were heavier (proportionately 0.3 heavier). The more remarkable difference was that carcasses of rabbits given the experimental diet had markedly less fat in scapular (5.8 v. 10.0 g) and perirenal fat (9.0 v. 22.3 g) deposits.No differences in cooking losses or water-holding capacity of the meat were found and also the colour was similar, but the b* parameter was a little lower for meat of the M group rabbits.The proportion of protein in the meat was the same for rabbits of the two groups, but rabbits given the experimental diet which had leaner carcasses also had leaner meat (19 v. 37 g lipids per kg meat) and a little more moisture (755 v. 736 g/kg meat). Intra and intermuscular fat of hindleg meat from rabbits of group M was less saturated and more unsaturated than that of the conventional rabbits mainly due to its higher proportion of polyunsaturated fatty acids, ω6 (37·3 v. 29·1 g/100 g lipids) and ω3 (3·4 v. 2·2 g/ 100 g lipids). Polyunsaturated: saturated ratio was higher in the mulberry group than in the lucerne group (1·15 v. 0·85) indicating a more desirable value in rabbits given the experimental diet, so meat of these rabbits could be considered preferable for human nutrition from this point of view.