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National audience; The effects of tryptophan (Trp) supplementation were investigated in growing pigs (n = 100 from 40 to 100 kg) fed ad libitum in a context of a reduction of the crude protein (CP) level. A control diet with a CP content close to the standard level (NP; 16.5%) was compared to four low CP diets (LP; 13.7%) gradually supplemented with L-Trp (0, 0.3, 0.6 and 0.9 g/kg for LP0, LP1, LP2 and LP3, respectively). All the diets were formulated to contain similar net energy (9.9 MJ/kg) and standardized ileal digestible (SID) lysine (Lys; 0.81%) contents. The actual SID Trp:Lys ratios were 22, 17, 20, 23 and 27% for NP, LP0, LP1, LP2, and LP3 diets, respectively. Growth performance decreased when pigs were fed a low CP diet without L-Trp supplementation (LP0 vs. NP, -160 g/d; P < 0.05). The average daily gain of pigs fed the LP1 diets was similar to that obtained with NP treatment (958 vs. 989 g/d; P > 0.05). Similar growth performances were measured in LP1, LP2 and LP3 groups. In our experimental conditions, the SID Trp:Lys ratio in growing pigs fed a low CP diet has to be at least 20% to optimize the growth performance.

Session : Alimentation; absent

Dans les systèmes d'élevage où l'alimentation est centrée sur l'herbe, l'éleveur recherche la maximisation du pâturage, qui peut passer par l'allongement de la saison de pâturage et la diminution des récoltes d'herbe. Cette exigence peut être en partie comblée par la mise en place de stocks d'herbe sur pied au printemps. Mais quelle est l'évolution de la qualité des stocks sur pied dans le cas du ray-grass anglais pâturé ? Dans un dispositif expérimental en pâturage tournant pour vaches laitières, 6 parcelles (3 paddocks x 2 génotypes) sont conduites en stock sur pied. Ces parcelles sont pâturées jusqu'à 3 dates différentes et des prélèvements à 21, 42, 63 et 84 jours de repousse permettent de suivre l'évolution de la qualité des couverts, évaluée par la composition biochimique et la disparition de la matière sèche in sacco dans le rumen de vaches laitières. Le facteur le plus important permettant de limiter la baisse de qualité des stocks est l'intervalle de jours entre la date de dernier pâturage et la date d'exploitation en stocks. Le deuxième facteur à prendre en compte est le positionnement de la date de dernier pâturage., In those stock-feeding systems where feeding is centred on herbage, farmers aim at maximizing grazing, which may be achieved through a lengthened grazing season and through diminished cuts. This requirement can be partly met by having foggage in spring. But how does the quality of this standing herbage change with time, in the case of grazed Perennial Ryegrass ? In a rotational grazing trial with dairy cows, 6 plots (3 paddocks x 2 genotypes) were used for foggage. These were grazed at three different ages, and samplings made at 21, 42, 63 and 84 days of regrowth indicated the changes in the quality of the herbage, estimated by its biochemical composition and by the in sacco disappearance of dry matter in the rumen of dairy cows. The main factor for the decrease in quality of the foggage is the interval in days between the last graze and the harvest of this foggage. Another factor to be taken into account is the date of the year at which the last graze does occur.