4.2. Switching to a diet richer in starch and fat at late growing period
This switch to a more concentrated diet at late fattening, when the incidence of digestive disorders is usually lower, was proposed to alleviate the detriment on carcass yield when using high NDSF diet. According to our results, this strategy was effective. Although animals apparently showed similar growth performance (feed intake, LW gain and FCR) with both diets, carcass weight was higher when animals were shifted to a more concentrated diet resulting in a higher dressing out percentage. The nutrient change to starch and fat instead of highly fermentable fibre explains the promotion of small intestine development and the reduction of caecum content which is the main factor responsible for full gastrointestinal tract development decrease. Ledin (1982) found that growing rabbits fed with a more concentrated diet had a longer small intestine.
However, the delay of maturity observed with the high NSDF diet was not alleviated when switching to a concentrated diet at late fattening, as deduced from a persisting high head proportion and low meat to bone ratio. In addition, improvement on chilled carcass weight observed was mainly due to the promotion of the liver development and fat deposition, both dissectible (Pla and Cervera, 1997 and Fernandez and Fraga, 1996) and meat fats (Christ et al., 1996), when an energy enriched diet was introduced. The increase in fat percentage in carcass and meat could be considered negative from the point of view of consumer health. However, rabbit carcass and meat can be considered low in fat (Ouhayoun, 1989 and Pla et al., 2004) compared to other species, and an increase of fat percentage in meat could have a positive effect on meat quality because juiciness is improved (AMSA, 1978).