CHRONOLOGIE DE L'APPORT AZOTÉ PENDANT LE CYCLE DE REPRODUCTION CHEZ LA TRUIE

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Abstract
This experiment was made during 2 reproductive cycles on 76 nulliparous Large White sows distributed into 3 groups only differing by the chronology of crude protein supply during the reproductive cycle. Group 1 (control) fed a diet with a low protein level during gestation (10%) and a high level during lactation (16%) was compared with group 3 recieving a diet with a constant protein level (13%) during the whole reproductive cycle and with group 2 given supplementary protein during late gestation (first 10%) and then 13% from day 75 of gestation) followed by a reduction of the lactation level (13%). During each stage of the cycle, daily feed intake levels were identical for the 3 groups, i.e., 2 kg during gestation 4.17 (1st cycle) and 4.84 (2nd cycle) during lactation, 2.5 kg between weaning and mating. The diet contained 3220 kcal digestible energy per kg and crude protein in the form of wheat replaced partially by soybean meal. During gestation, a 30% increase in the intake of crude protein significantly enhanced the weight gain of the sows during the 2 cycles studied. Increase of gestation net gain (group 3 relatively to group 1) was 32% (1st cycle) or 66% (2nd cycle). The growing consumption of crude protein during the last-3rd of gestation (group 2) also increased the net weight gain of the animals: 36.5 kg vs. 30.4 in group 1 (1st cycle), 24.1 vs. 19.6 in group 1 (2nd cycle). Around day 82 of gestation, a study made on almost half of the animals from each group kept during 2 cycles in metabolism crates also showed an increase of the N balance at the higest dietary protein level. N retention (g per day) in group 1, 2 and 3 was 8.3, 15.5 and 12.5, respectively, during the 1st cycle and 3.7, 10.8 and 11.7 during the 2nd cycle. The protein supply during gestation did not affect either the litter size or the mean weight of the piglets at parturition The mean number of piglets (14.2) weaned by the sows having realized 2 lactations was not affected by the amount of crude protein ingested by the dams. During the 1st lactation (35 days) the growth of the suckled piglets or the litter gain were comparable for the 3 groups, but lowering the protein intake during lactation (groups 2 and 3) increased the weight loss in the dams: 17.7 kg (group 2) and 15.0 kg (group 3), vs. 4.8 kg (group 1). During the 2nd lactation, a non significant decrease in piglet weight at weaning was recorded in group 3 (7.2 kg vs. 7.5 kg in group 1) and notably in group 2 (6.9 kg). This retardation of piglet growth was mainly marked from day 21 of lactation. The litter gain was also lower in group 2 (38.8 kg) than in group 1 (49.15 kg). That of group 3 was located between the 2 other groups (45.15 kg). The milk composition of the sows was determined after 15 days of lactation. During the 2 cycles, the dry matter content was larger in group 1 (19.3% during the 1st cycle and 18.45 during the 2nd cycle) than in group 2 (18.0 and 17.9%, respectively) or group 3 (18.25 and 17.4%, respectively). Parallel to that the energy values of milk dry matter were higher in group 1 (6207 kcal during the 1st cycle, 6251 kcal during the 2nd cycle) than in group 2 (6137 and 6000 kcal, respectively) or group 3 (6161 and 6025 kcal, respectively). Reducing the protein supply during lactation for growing primiparous sows is probable if this supply is enhanced during gestation period or part of this period. In adult sows the use of gestation protein reserves was not sufficient to obtain a litter gain comparable to that recorded in animals receiving a larger supply of protein during lactation.