BREED AND ENVIRONMENTAL-EFFECTS ON POSTWEANING GROWTH OF RABBITS

Growth records of 4,270 weanling rabbits born between March 1985 and D ecember 1989 were studied to evaluate the effects of breed and month o f birth on postweaning growth performance of four medium-sized breeds: Californian (CAL), New Zealand White (NZW), Palomino (PAL), and White Satin (WS). Traits examined were 28-d weaning weight (WW), postweanin g gain (GAIN), attainment of 1,600-g market weight by 76 d of age (MKT ), and approximate age at 1,600 g (AGE). Least squares models included breed, month of birth, sex, and year of birth as fixed effects and li tter within breed by month and by year and the residual as random vari ables. The NZW had significantly higher GAIN and MKT and lower AGE tha n the other three breeds. White Satin had the highest WW, followed by CAL, NZW, and PAL. White Satin had higher GAIN and lower AGE than PAL or CAL but did not differ for MKT. Poorer performance was seen during the summer, but the NZW tended to be less affected by the environmenta l extremes than the other breeds. The effects on GAIN of mean monthly temperature and daylength and the interrelationships of these with est imated milk production and litter size at weaning were evaluated by re gression methods for the 2,100 NZW fryers. Temperature and daylength h ad significant effects on GAIN, with lowest GAIN in the summer, but th e individual contributions to the variance were small because of some redundancy when month, temperature, and(or) light were included in the same model. Curvilinear trends were observed that favored GAIN as est imated milk production increased but decreased GAIN as litter size at weaning increased. In the hot, humid climate of southern Louisiana imp ortant breed differences were noted. There were also indications that daylength may be an important factor in postweaning fryer performance.