Effect of crude fat and crude protein on reproduction and weaning growth in four strains of inbred mice.

Diets made from natural ingredients were fed to four inbred strains of mice (BALB/cAnN, C3H/HeN, C57BL/6N and DBA/2N) to study the effects of different concentrations of dietary crude protein, 18% and 24% with crude fat concentrations of 4%, 8%, and 12% on reproduction and weanling growth. The parameters measured included the number of litters and pups born, the number of litters and pups weaned, weanling mortality and weanling weight. Neither crude protein nor crude fat concentrations had significant effects on any of the reproductive parameters tested. However, a significant fat x protein interaction was observed for reproduction. These results indicate that the absolute concentrations of crude protein and crude fat in diets for inbred mouse production are not as important as the ratio of these two nutrients. There was also a differential response in reproduction among the strains due to the level of fat which indicates different dietary requirements for fat among these four inbred strains for maximum reproduction. In contrast to the results for reproduction, crude protein and crude fat independently had significant effects on weanling weight, but there was no effect due to the ratio of the nutrients. There was a significant increase in the weanling growth rate for all four strains as the dietary fat level increased, but a decrease in growth rate as the protein level increased. The reduced growth rate due to the increased protein was not of the same magnitude for all four strains which indicates specific protein requirements among the strains for weanling growth.