1. New Zealand White (NZW) rabbits were given, between 4 and 8 weeks of age, a range of diets, based on oats and fish meal, containing from 104 to 255 g crude protein (nitrogen x 6.25; CP)/kg to establish the level of CP below which growth was retarded. 2. In three experiments each diet was fed to four animals and food intake, growth and N balance were measured over 4 weeks. Body analysis was also carried out after two of the experiments. 3. The rates of food intake and growth of animals increased with dietary CP concentration until a CP concentration of approximately 150 g/kg diet had been reached. Beyond this there was little further improvement. N balance studies showed that once this dietary concentration of CP had been reached, there was a reduced rate of N retention. 4. Good agreement was found between N retention measured by balance methods and by body analysis: body composition showed a tendency towards an increase 5. Microbial protein produced in the caecum and eaten during coprophagy, was found to supplement the dietary protein by approximately 2 g CP/d, or by only 0.1 of a normal dietary intake of CP. 6. In the second part of the study NZW rabbits were offered, between 5 and 8 weeks of age, diets based on oats containing 150 g CP/kg. The protein supplied by oats was supplemented with maize gluten, gelatin, groundnut meal, casein, soya-bean meal or fish meal. 7. Rabbits offered diets containing casein, soya-bean meal and fish meal gained 40-50 g/d similar, to animals given a well-balanced control diet, while those given diets containing maize gluten, gelatin or groundnut meal gained approximately 30 g/d. This indicated that amino acid balance in dietary protein was important to the growing rabbit. 8. In later experiments, diets based on cereals and groundnut meal supplemented with varying amounts of lysine and methionine were offered during a 3-week-post-weaning period in order to assess requirements for those limiting amino acids. 9. The addition of both lysine and methionine improved growth rates. The minimum requirements for normal growth were found to be 6.2 g methionine+cystine and 9.4 g lysine/kg diet.
New Zealand White rabbits, aged between 5 and 8 weeks, were offered diets based on oatmeal together with up to 500 g kg−1 of ground oat husk, or 500 g kg−1 of ground barley straw or 400 g of a purified cellulose. The rabbits gained about 40 g liveweight per day when fed a well‐balanced control diet (in which oatmeal, grassmeal, corn oil and fishmeal were the main constituents) and, apart from one occasion, there was no significant reduction in this rate of gain even when the diets offered contained up to 500 g kg−1 of these fibre sources. Food consumption increased from 80 g day−1 to 115 g day−1 as the acid detergent fibre concentration in the diet increased from 39 to 270 g kg−1. Digestible and metabolisable energy contents of the diets fell as the fibre concentration rose but the rabbits were able to adjust their intakes and maintain their daily metabolisable energy intakes constant at about 1100 kJ. The proportion of fat in the body dry matter fell as the fibre concentration in the diet was raised. A minimum dietary fibre content of 100 g kg−1 as measured by the acid detergent fibre or crude fibre techniques is suggested for optimum healthy growth.
Young meat rabbits of the New Zealand White breed, aged between 5 and 8 weeks, were fed semi-purified diets containing casein as the main protein source, and increasing levels of supplementary arginine to assess their requirements for dietary arginine. On all experimental diets the rabbits achieved good mean growth rates which were not significantly different from the growth rate of 42 g day-1 on a welltried control diet. The results are discussed with reference to studies by other workers and the conclusion reached that the requirement for arginine is not greater than 5.6 g kg-1 diet as fed.
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