The effect of changes in concentrations of dry matter, and of fat and protein in milk substitute diets for veal calves

Abstract

SUMMARYThe effect of a gradual increase in dry-matter concentration from 140 g/kg (LD diets) to a maximum of 215 g/kg (HD diets), and the effect of an increase in fat concentration from 225 g/kg D.M. and reduction in protein concentration from 298 g/kg D.M. (LF diets) to 254g fat and 211g protein/kg D.M. respectively (HF diets) was examined with 32 Friesian bull calves in a 2 × 2 factorial experiment. Milk substitutes were offered ad libitum in two feeds daily from 2 days of age. The dietary changes were first introduced at 7 weeks of age and differences became progressively greater as further changes were made at 9, 11 and 13 weeks. The calves were slaughtered at 16 weeks of age.Dry-matter intake for calves given the HD diets increased faster with age after 7 weeks than that for calves given the LD diets. For the period 7–16 weeks, calves given the HD diets consumed 17% more D.M. than those given the LD diets and had a 13% greater rate of live-weight gain (1·57 v. 1·39 kg/day), although most of the increase in weight gain occurred between 9 and 13 weeks of age.There was no significant effect on D.M. intake or on live-weight gain of altering the fat and protein concentrations in the milk substitute, although feed conversion ratio (kg D.M. intake/kg weight gain) was higher for the HF than for the LF diets. Apparent digestibility of D.M., crude protein and fat were reduced with the HF diets, but the efficiency of retention of the digested nitrogen was improved. During the second and third weeks of life, D.M. intake reached a peak at approximately 67 g/kg0·75 and subsequently declined to stabilize at about 56 g/kg0·75. However, a gradual increase in concentration of the milk substitute from 140 to 215 g D.M./kg increased intake to about 62 g D.M./kg0·75. The results clearly indicate that, at a dietary concentration of 140 g D.M./kg, maximum D.M. intake cannot be achieved because the volume of fluid that needs to be ingested exceeds the capacity of the digestive system. In contrast, at reconstitution rates increasing from 140 to 215 g D.M./kg, distension of the stomach becomes less important and physiological and metabolic factors seem to assume a greater role in the control of feed intake.