Effects of Dietary Crude Protein on Protein and Fat Deposition in Milk-Fed Veal Calves

Abstract

Research on veal calf production has focused on maximizing lean tissue growth. Nevertheless, limited attention has been paid to the evolution of digestive and metabolic utilization of N and energy as calves get older, whereas age at slaughter increases. The objective of this study was to determine the effects of 4 concentrations of dietary crude protein (CP) content on protein and fat deposition and energy utilization in milk-fed calves at 3 stages of fattening using the balance technique combined with heat production measurements in a respiration chamber. At each stage, 16 Prim'Holstein male calves (mean body weight at each stage: 72, 136, and 212 kg) received 4 isocaloric diets with CP contents of 76, 88, 100, and 112% of a reference CP content fixed at 20% during the first stage and 19% during the 2 later stages. After 2 wk of adaptation to their respective diets and housing conditions, the calves were placed for 1 wk in an open-circuit respiration chamber for N and energy balance measurements (first 6 d) and measurement of the fasting heat production (last day). Measurements for a stage were performed over 2 periods of 4 successive weeks. There was no effect of dietary CP on digestibility during the 2 later stages, but the low-protein diet resulted in lower digestibility coefficients for dry matter, organic matter, gross energy, CP, and crude fat during the first stage. Endogenous fecal N was estimated as 2.5 g/kg of dry matter intake irrespective of stage, and metabolic urinary N was estimated at 0.07 g/kg of body weight(0.85) per day. Maximum N retention was 32.8, 40.5, and 44.0 g/d at stages 1, 2, and 3, respectively. The effect of protein intake on protein deposition was dependent on age of the calves, because the marginal efficiency of digestible protein utilization decreased from 64 to 18% as animals got older. Fat deposition decreased with increasing dietary CP content irrespective of stage. Total energy retention was not modified by dietary CP content. The composition of body weight gain was affected differently for each stage, because the protein content of body weight gain increased with increasing dietary CP content during the first stage, whereas it remained constant during the other 2 stages. Fat and energy content in body weight gain decreased with increasing dietary CP irrespective of stage. These results provide a basis for estimating protein requirement of veal calves according to a factorial approach.

Effect of feed intake on heat production and protein and fat deposition in milk-fed veal calves

“…Values for the first stages are in agreement with previous results (Donnelly and Hutton, 1976;Diaz et al, 2001) with calves receiving high quantities of protein in their diets and they are also close to the value used by the NRC (187 g/kg BW gain, NRC, 2001). However, the protein content of BW gain for the oldest calves is higher than that measured by Meulenbroeks et al (1986) or values measured previously in our group (Labussiè re et al, 2008b), although they are consistent with results of Vermorel et al (1974). As lipid content also increases as animals get older (Vermorel et al, 1974, Table 5), this indicates that the water content of BW gain would decrease as calves get older (Robelin, 1986).…”

“…They agree with values previously measured for similar diets (Roy et al, 1970;Ternouth et al, 1985;Gerrits et al, 1996;Labussiè re et al, 2008b). The digestibility coefficient for crude fat tended to increase with age while the crude fat content of the diets were similar.…”

“…This may indicate that a maximum PD was not reached and that PD was first limited by feed intake. Additionally, the ratios between digestible N and ME in the milk replacers (1.87 g/MJ for grower and 1.69 g/MJ for finisher diet) were close or higher to the requirements of veal calves (Labussiè re et al, 2008b). Consequently, the slopes for PD in Table 5 may not be biased by the animal potential for protein deposition or by insufficient protein allowance.…”

“…During the adaptation period, both cages were placed in the same room but separated by a curtain to avoid visual contact between the two calves. They were bucket-fed automatically without direct human contact just before drinking according to Labussiè re et al (2008b). Calves were harnessed with plastic bags 2 days before their entrance in the respiration chamber allowing for total feces collection.…”

“…Gas concentrations (CO 2 , O 2 and CH 4 ) of outgoing air and ventilation rate were continuously recorded (60 times per second) and averaged over 10-s intervals according to procedures described by van Milgen et al (1997) and Labussiè re et al (2008b). The urinary nitrogen losses in the air, recovered in condensed water and outgoing air, were collected according to the methods described by Noblet et al (1987).…”