Note sur la valeur azotée de fourrages pauvres traités par l'urée ou l'ammoniac

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Abstract
Late maturing natural-meadow hay and wheat straw were treated (under sheet) with ammonia (3 p. 100) or urea (5 p. 100). Untreated and treated forages were offered to normal or rumen-fistulated sheep. Animals receiving untreated wheat straw were also given 100 g soyabean oil-meal per day. Ammoniation resulted in a marked rise in forage crude protein content (+85 and +60 g/kg DM), feed intake (+26 and +9 p. 100) and organic matter digestibility (+7.9 and +7.7 points). Urea treatment was not efficient. The forage crude protein content increased (+111 and +48 g/kg DM), but the straw intake decreased by 17 p. 100 and the organic matter digestibility remained unchanged. This was due to a poor transformation of urea into ammonia (on an average only 19 p. 100 for the two forages). Treatments, especially with ammonia reduced the cellulolytic activity in the rumen in the case of hay, but the opposite was observed with straw; the digestion rate of straw increased, but not that of hay. Treatments also led to a higher ammonia concentration in the rumen. Ammonia treatment led to a lower nitrogen retention in the animals. Thus, it seems that the nitrogen nutritive value of ammonia treated forages is rather low despite a large nitrogen supply. However, the cellulolytic activity is perhaps not reduced by the treatment in all cases. Urea treatments are developing and give positive results; they should be adapted to our forage and treatment conditions.