Utilisation des tourteaux traités au formol par les vaches laitières. I. — Aspects digestifs

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Abstract
The effects on digestion of treating oil-meals with formaldehyde were studied in rumen or duodenum fistulated cattle. Soybean and rapeseed meals were treated separately with formaldehyde at the rate of 0.3 and 0.4% dry matter (DM), respectively. The whole experiment lasted 2 yr. Proportion of degradable N in the oil-meals was calculated from net ammonia production during in vitro incubation with a large amount of rumen content and juice for 6 h. For normal and treated oil-meals, degradation was 43 and 1% respectively, for soybean (1st year), 25 and 3% for rapeseed (1st year), and 42 and 5% for a mixture 50/50 of soybean-rapeseed (2nd yr). Rumen fistulated cows (8) in two 4 .times. 4 latin square trials, were given a limited amount of maize silage with meals (accounting for 50% of total N intake). In trial 1, soybean and rapeseed meals were given separately, either normal or treated. In trial 2, they were mixed and given either normal or treated, with or without urea. Treatment of oil-meals slightly decreased N digestibility in trial 2; the digestability of other diet components was unaffected. N balance was improved mainly in trial 1, and rumen ammonia level was decreased mainly in trial 2. Rumen volatile fatty acids [VFA] were not affected excepted a decrease in branched VFA. Two young duodenal fistulated animals were given a limited amount of maize silage with either normal or treated soybean meal in 2 reverse periods. Site (rumen or intestine) of disappearance of non N components was not affected. With treated soybean, duodenal contents (but not feces) contained more N in DM, with a greater proportion of amino N. Flow of amino acids was increased by 20% without modification of their intestinal digestibility. Increase was greatest for arginine, phenylalanine and histidine and lowest for methionine, threonine and lysine. AA extra-flow associated with treatment of 1 kg DM of soybean meal was near 100 g and the AA composition of this supplement was quite the same as that of the untreated soybean meal.