EFFECT OF DIETARY CRUDE PROTEIN LEVEL ON PROTEIN AND ENERGY BALANCES IN GROWING PIGS - COMPARISON OF 2 MEASUREMENT METHODS

The effect of dietary crude protein level (17.7: L or 24.3%: H), on ni trogen (N) and energy utilization between 20 and 50 kg body weight, wa s studied in six groups of two littermate pigs fed close to their ad l ib. level. Nitrogen (collection of excreta) and energy (indirect calor imetry) retentions were estimated by continuous balance; results were compared to those obtained on the same pigs by the comparative slaught er technique. Initial body composition of each group of experimental p igs was estimated from other two littermates slaughtered at the beginn ing of the experiment. Gaseous N, methane losses and N and energy in d igesta were also measured. The L pigs retained more energy as fat (7.9 6 vs 4.94 MJ/d), and less energy as protein (3.19 vs 4.02 MJ/d) than H pigs. The balance technique overestimated the energy retention (+4.4% ) and nitrogen retention (+2.5%) as estimated by the comparative slaug hter technique. The discrepancy for N doubles when evaporation N losse s were not taken into account. The higher discrepancy in energy retent ion measurement could be related to the accuracy in estimation of the initial body energy content, or with the underestimation of heat produ ction by the equation of Brouwer (1965).