The effect of different levels of protein degradability in starter- and finishing diets on veal calf performance

[摘要] ENGLISH ABSTRACT:Veal production is a specialised form of calf rearing in which calves were traditionallyraised on all-liquid diets. The early weaning of calves onto concentrated diets providesan economically viable alternative rearing method with comparable calf performance.The emphasis in meat production has shifted to the production of lean meat, thereforethe deposition of protein instead of fat has become a priority. The optimum level ofdietary crude protein for growing calves is well established. Very little, however, isknown about the influence of protein degradability in the diet of young ruminants.Recommendations by the NRC are derived from data obtained using lactating dairycows. The aim was to obtain data on which recommendations for the level ofdegradable protein in starter and finisher diets for calves could be based.Two experiments were conducted to examine the effect of different levels of dietarycrude protein degradability in starter and finisher calf diets on veal calf performance. Inboth experiments Holstein bull calves were 3 - 10 days of age at the onset, weaned at 4weeks of age and slaughtered at 20 weeks of age for veal. In Experiment 1 calves wererandomly assigned to one of three treatments: low (LO), medium (MD) and high (HO)rumen degradable protein. Calves received a starter diet up to 11 weeks of age andfinisher diets from week 12 - 20. In Experiment 2 calves received a starter diet eitherhigh or low in rumen degradable protein up to 10 weeks of age. In the finishing period(week 11 - 20) both the low and high groups were again divided into a low and highgroup, resulting effectively in 4 treatments, viz. LL, LH, HL and HH. The diets in bothexperiments were formulated to be iso-nitrogenous and iso-caloric, differing only inrumen undegradable protein content within periods and. respective experiments. Body weight gain, feed intake and feed conversion efficiency data for the preweaning,starter, finishing and total experimental period was compared between treatments.There were no significant differences for feed intake, body weight gain or feed efficiencyin the starter period of both experiments between treatments. In the finishing period ofExperiment 1 the average daily gain for the LO treatment was significantly higher thanfor the HO treatment, with the MD treatment having an intermediate value. The feedconversion ratio (FCR) for the LO treatment was also significantly better than for theother two treatments. In Experiment 2 the FCR tended (P = 0.0984) to differ betweentreatments in the finishing period. Calves from the LL and HL treatments had a morefavourable FCR than calves from the LH treatment. The HH treatment had anintermediate FCR. According to these results crude protein degradability appears tohave an effect on the FCR in the finishing period.The lack of response to higher levels of undegradable dietary protein in calves youngerthan 10 weeks may be due to underdeveloped rumen functions and it seems possiblefor high degradable protein to escape degradation to a higher extent than at a later age.In a third experiment, Holstein bull calves and Holstein cows were used to determineand compare the dry matter and crude protein degradability of the four calf diets used inExperiment 2. Rumen VFA concentrations, pH level and NH3-N concentrations weremeasured for the cannulated Holstein calves to evaluate the level of rumen metabolicmaturity of growing calves. Five Holstein bull calves were ruminally cannulated at 6weeks of age. Dry matter and crude protein degradability were determined once weeklyfrom week 8 - 20 by means of 24 h in sacco incubations. Three ruminally cannulatedHolstein cows were used to determine the comparable values for mature ruminants.Dry matter and crude protein degradability differed significantly between the low andhigh degradable diets for both calves and cows. Dry matter and crude proteindegradability in calves increased up to 11 and 12 weeks of age respectively, and thenappeared to remain constant to week 20. Dry matter and crude protein degradabilityvalues of the starter diets were lower for the calves than for the cows, but values weresimilar for the finisher diets. Rumen VFA concentrations, pH level and NH3-Nconcentration showed some fluctuation between weeks, but were similar to literaturevalues for mature animals.

[发布机构] Stellenbosch University