Response of growing rabbits in growth performance and carcass composition to balanced dietary protein.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.

The broad objective of the study was to measure growth performance and carcass composition of growing rabbits as influenced by the dietary protein levels. A 56-day feeding trial was conducted to measure the response of two rabbit breeds in growth performance and carcass composition to balanced dietary protein. A total of 72 sexed rabbits at the weaning age of 5-6 weeks were weighed upon arrival at the farm and randomly distributed singly to 72 grower cages of 61 x 60 x 58 cm. The breeds used were New Zealand White (NZW) and Californian (CAL) rabbits with equal numbers of males and females per breed. A representative sample of 8 New Zealand White rabbits was slaughtered before the beginning of the feeding experiment to estimate the initial carcass composition of the remaining NZW rabbits used in the response experiment. All the remaining rabbits were subjected to the experimental dietary protein treatments that were a result of blending low and high protein basal diets to produce four additional intermediate diets that resulted in a total of six experimental diets (126, 143, 161, 178, 196, 213g/kg). The trial was divided into two periods, from 1-28d and from 29-56d, respectively. Feed intake, body weight gain, and carcass composition were measured. At the end of the feeding trial, 48 rabbits (24 from each breed with equal numbers of males and females within each breed) were sampled for carcass analysis. These were analysed for moisture, ash, lipid, and protein content. Standard methods were used to determine the chemical composition of the rabbit carcasses. Appropriate regression models, including exponential, quadratic, and linear, were fitted to the data where relevant. The model with the best statistical fit was selected. Daily feed intake and final body weights were significantly influenced by the dietary protein levels (P < 0.05). Dietary protein did not influence feed conversion efficiency (FCE), (P > 0.05). The highest feed intakes, body weight gain, and consequently FCE’s were observed in the NZW breed. The NZW male rabbits exhibited highest feed intake and body weight gain while NZW female rabbits had the highest FCE. Significant interactions were detected in feed intake and body weight of the two breeds (P < 0.05). Female rabbits of the two breeds showed a significant interaction in feed intake and final body weight to the dietary protein levels. Moisture, ash, lipid, and protein in the carcass were not affected by the dietary protein content (P > 0.05). No significant (breed x sex) or (protein x breed x sex) interactions were observed in the carcass composition parameters. CAL rabbits had higher ash, lipid and protein and lower moisture contents than the NZW rabbits. Fat content was increased as the dietary protein content was reduced (P > 0.05). As a result, both males and females of the NZW breed had highest lipid contents on the lowest dietary protein level. CAL females and males had higher protein contents than NZW female and male rabbits, respectively. Carcass and pelt weights exhibited a significant response to the dietary protein levels (P < 0.05). Significant interactions in carcass and pelt weights were observed (P < 0.05). Considerable variation within treatments in all responses measured in this study meant that the responses to dietary protein could not be accurately described. Solutions to this problem would be to use more rabbits per treatment, to sample more rabbits per treatment, and to check on the accuracy of the laboratory analyses. Widening the range of dietary protein levels may result in a greater difference in the response of the rabbits to protein, thereby describing this response more accurately.