Effects of Intraruminal Infusions of Mineral Salts on Volatile Fatty Acid Production in Steers Fed High-Grain and High-Roughage Diets

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Abstract
Four rumen fistulated Holstein steers were used to assess the effects of intraruminal salt infusions on various rumen characteristics including volatile fatty acid production rates. In the first experiment, the basal diet consisted of 75% concentrate and 25% corn silage (high-grain diet). The experimental design was a 4 .times. 4 Latin square in which the four treatments were: intraruminal infusion of 8 l of water (control) or 8 l of water plus 288 g sodium bicarbonate, 200 g sodium chloride or 600 g sodium chloride. In the 2nd experiment, procedures were the same except the basal diet consisted of 64% aflalfa hay and 18% each of corn silage and concentrate (high-roughage diet). When the high-grain basal diet was fed, intraruminal infusions of mineral salts increased dilution rate of rumen fluid. Total fluid flow from the rumen also was increased by salt infusions with sodium bicarbonate and the most sodium chloride (600 g/day) exerting greatest effects for both dietary regimens. Salt infusions reduced the molar percentage of rumen propionate and increased the molar percentage of acetate when the high-grain diet was fed. These same treatments were without effect on molar percentages of rumen acids when the high-roughage diet was fed. The change in the molar percentages of acetate and propionate on the high-grain ration was solely from reduction in propionate production. The lower production of propionate, from salt infusions, may have occurred because of the washout of readily fermentable materials. Dry matter disappearance from feeds placed in dacron bags and suspended in the rumen was unaffected by infusion of mineral salts.

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