The effect of age on in sacco estimates of rumen dry matter and crude protein degradability in veal calves

This study was conducted to determine whether rumen dry matter and crude protein degradability in calves aged 8-10 weeks differs from that in mature cows. Five Holstein bull calves were rumen-fistulated at six weeks of age and were used in consecutive weekly 24 h trials from 8-20 weeks of age. Dry matter and crude protein degradability of two starter and two finisher veal calf diets of high or low rumen degradable protein content were estimated from 24 h in sacco incubation. Rumen pH and concentrations of volatile fatty acids and ammonia-nitrogen were determined on a weekly basis. Three rumen-fistulated Holstein cows were also used to evaluate dry matter and crude protein degradabilities of the diets. Estimates of dry matter degradability obtained from calves differed between the low and high degradability diets within weeks. Dry matter degradability differed between the starter and finisher diets (weeks 10 and 11) and remained fairly constant from week 11 to week 20. Crude protein degradability in calves also differed between the low and high degradability diets within weeks. Crude protein degradability increased up to week 12 and then remained constant until week 20. Dry matter and crude protein degradability estimates for the starter diets were both lower than the corresponding values obtained with cows, while estimates for finisher diets were similar. There were no clear trends over time for rumen pH, volatile fatty acid concentrations and ratios, or for rumen ammonia-nitrogen concentrations ion calves. These values showed a degree of variation between weeks and were similar to literature values for mature ruminants. (South African Journal of Animal Science, 2000, 30(3): 212-219)