Effect of solid feed on energy and protein utilization in milk-fed veal calves

Little knowledge on the digestive and metabolic utilization of solid feed in veal calves is available. The objectives of the study were to determine the effects of 2 solid feeds offered at 2 feeding levels (FL90 and FL105) in addition to a milk replacer on heat production (HP) and protein and fat deposition in veal calves. Sixteen calves (148.0 +/- 3.7 kg) received milk replacer (75% of a reference DE allowance) and solid feeds that consisted of corn grain and pelleted hydrolyzed wheat gluten without (CO) or with (CS) chopped wheat straw. The solid feed supply provided 15 or 30% of the reference DE allowance to achieve FL90 or FL105, resulting in 4 treatments: CO90, CS90, CO105, and CS105. A fifth treatment consisted of using the milk replacer alone at FL90 (treatment M90) and was measured in 4 other calves. All calves were kept individually for 7 d in a respiration chamber to estimate energy and N balances and fasting HP. The digestibility coefficients of DM, OM, GE, and major nutrients were at least 94% for M90 and decreased when solid feed was added (P < 0.05). Methane production was negligible in M90 calves and increased when solid feed was given (ranging 8 to 23 L/d between CO90 and CS105, P < 0.01), indicative of ruminal fermentation. The provision of increasing amounts of solid feed decreased urinary energy in connection with a tendency (P = 0.09) for a reduction of urinary glucose excretion. The metabolizability of DE was greater with the milk replacer (95.6%) and decreased when straw was added (P < 0.01). Neither CO90 or CS90 affected HP and total energy retention (P > 0.05). Dietary treatment had no effect (P > 0.05) on activity HP (53 kJ/kg of BW(0.85) daily) but did affect thermic effect of feeding; efficiency of utilizing ME for maintenance and growth was greatest for the M90 calves (84.5%, P = 0.02). Fasting HP tended (P = 0.09) to increase at the greatest FL (308 vs. 298 kJ/kg of BW(0.85) daily). Maintenance ME requirement increased (P = 0.04) from 364 to 382 kJ/kg of BW(0.85) daily when feeding level increased (P = 0.04) but was not affected by ingestion of solid feed. The provision of solid feed to veal calves was associated with a reduced efficiency of N retention (P = 0.04), and energy retained as protein tended to decrease (P = 0.08), probably as a result of an imbalanced AA supply of the solid feeds. The data were used to calculate the energy contents of solid feed. The utilization of energy from solid feed differed from that of milk replacer.