THE INVESTIGATION OF SODIUM BICARBONATE OR BENTONITE AS SUPPLEMENTS IN SILAGES FED TO LACTATING COWS

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Abstract
Two experiments with lactating Holsteins were carried out to determine the effectiveness of sodium bicarbonate (NaHCO3) or bentonite, added to silage prior to feeding, as a means of increasing dry matter intake. In the first trials the feed, consisting of 10% grain mixture, 45% grass silage and 45% corn silage, was supplemented with 0, 0.6 or 1.2% bentonite in a 3 × 3 latin square utilizing 12 cows and 28-day test periods. Neither level of bentonite improved dry matter intake or milk yield. Milk composition, molar proportions of rumen volatile fatty acids, plasma calcium and phosphorus were not influenced by additions of bentonite. Apparent dry matter digestibility was significantly reduced (P < 0.05) by the addition of bentonite at the 0.6 and 1.2% levels compared to the cows fed the unsupplemented ration. The digestibility of acid detergent fiber was lower (P < 0.05) for cows fed the silage mixture supplemented with 1.2% bentonite than for the controls. In the second trial a silage mixture consisting of approximately 30% grass silage and 70% corn silage was supplemented with either 0.8% NaHCO3, 2.1% bentonite or neither and fed in a 3 × 3 latin square utilizing 15 cows and 28-day treatment periods. Compared to control cows, neither NaHCO3 nor bentonite had any significant (P > 0.05) influence on dry matter intake, milk yield or rumen fermentation. However, the addition of NaHCO3 to the silage improved milk yield and feed conversion (P < 0.05) when compared to cows fed the silage supplemented with bentonite. It was concluded from these trials that bentonite should not be used as a supplement to silage diets fed to lactating cows. The results suggested that NaHCO3 supplementation had little if any beneficial effect when grass silage made up approximately 30% of the total diet. Key words: NaHCO3, bentonite, lactating cows, silage intake, digestibility