EFFECT OF PROTEIN AND PROTEIN-FREE ENERGY-INTAKE ON PROTEIN AND FAT DEPOSITION RATES IN PRERUMINANT CALVES OF 80 TO 240 KG LIVE WEIGHT

Two experiments were conducted to quantify the effects of protein inta ke on protein and fat deposition rates at two protein-free, energy int ake levels in 90 preruminant Holstein Friesian x Dutch Friesian calves . The two experiments were similar in design, but were performed in tw o different weight ranges: 80 to 160 kg BW and 160 to 240 kg BW in Exp . 1 and 2, respectively. In each experiment, calves were allocated to either an initial slaughter group or to one of 12 treatments (three ca lves per treatment), which consisted of six protein intake levels at e ach of two protein-free energy intake levels. Calves were slaughtered and analyzed for body composition when they had reached the target wei ght. A balance study was conducted when calves reached 120 and 200 kg BW in Exp. 1 and 2, respectively. Protein digestibility increased with increasing protein intake in both experiments (P < .001). Average dai ly gain of the empty body varied between 640 and 1,340 g/d and between 420 and 1,370 g/d in Exp. 1 and 2, respectively, and was affected by protein (P < .001) and protein-free energy intake (P < .001). The calv es responded to increased protein intake by increasing their protein ( P < .001) and fat (P < .01) deposition rates. Maximum protein depositi on was reached in the second experiment at 244 g/d. Extra protein-free energy intake resulted mainly in extra fat deposition (P < .001), but also increased the protein deposition (P < .01), even at low protein intake levels. In both experiments, the response of protein deposition rate to increased protein intakes was low: about 30% of the extra ing ested protein was deposited. These results clearly demonstrate a low p riority for partitioning dietary protein into protein gain in these ca lves.