Effets comparés des traitements à l'ammoniac et à la soude sur la valeur alimentaire de fourrages pauvres

Open Access
Publisher Website
Google Scholar
Abstract
In 3 trials with poor-roughages (a late harvested grass hay, a wheat straw and a rice straw) the effects of NaOH treatment were compared to those of a NH3 treatment. Ammonia-treatment was made with 40 g of NH3 per kg using the Norwegian method in Aug. Soda treatment was performed 48 h before feed distribution using a semi-wet process (2.5 l of a solution containing 16 g NaOH/kg forage). Roughages were given a to normal sheep in the following conditions: untreated forage, ad lib; NH3-treated forage, ad lib; NaOH-treated forage, ad lib; NH3-treated forage, restricted to the same level as untreated; NaOH-treated forage, restricted but only for rice straw. Wheat straw was given to rumen fistulated sheep, in the above conditions. Wheat and rice straws were supplemented with concentrates. The influences of 2 types of concentrates (maize and beet pulp) were also compared with the rice straw. The chemical composition of roughages and concentrate are given. Ammonia treatment increased the crude protein content of the 3 roughages especially for hay (+87 g/kg DM [dry matter]). For wheat straw, the crude protein level only reached a low value (85 g/kg DM). Both treatments greatly increased the voluntary feed intake of the roughages studied in the same way for hay and wheat straw (+37/100 on an average). NaOH-treatment was more efficient on rice straw (+62/100, vs. +31/100 for NH3 treatment). Both treatments increased organic matter digestibility (+8.9 with NH3 and +13.5 with NaOH), especially for the straws, in which soda was more efficient than ammonia. Replacing maize concentrate by pulp concentrate had only a limited effect on the digestibilities of the rice straw whether or not it was treated by NH3. Ammonia-treatment strongly increased the indigestible crude protein content of the forages (+22 g/kg DM). This level was higher with maize concentrate, compared to pulp concentrate. Nitrogen retention was higher in animals given NaOH-treated wheat straw. For this diet based on wheat straw the volatile fatty acids concentration in the rumen juice was higher with the NaOH-treatment than with the NH3-treatment (88 against 78 mmol/l. The NH3 concentration in the rumen juice was higher in the NH3-treated straw (25 mg/100 ml) and was harmless for the animals. It was lower for the NaOH treated straw (12 mg/100 ml). The straw treatments, especially with ammonia, decreased the cellulolytic activity of rumen microflora. In spite of a slightly lower feed efficiency when compared to NaOH-treatment, NH3-treatment increased the value of poor roughages. The problem of the nitrogen value significance of NH3-treated forages remains to be solved, as that of the low cellulolytic activity due to their consumption.