SULFUR METABOLISM AND NUTRITIONAL CHANGES IN LACTATING COWS ASSOCIATED WITH SUPPLEMENTAL SULFATE AND METHIONINE HYDROXY ANALOG

Abstract

A split-plot 4 × 4 latin square experiment using four Holstein cows was designed to determine the effects of adding either the calcium salt of 2-hydroxy-4-(methylthio)-butyric acid, or a mixture of potassium and magnesium sulfates, or a combination of both sulfur supplements, to a basal diet containing corn silage and grain concentrate mixture. Methionine hydroxy analog (MHA) was consumed at the level of approximately 25 g per day. Sulfates were added to the concentrate in amounts sufficient to elevate the sulfur concentration of the total diet to 0.20%. The addition of 25 g of MHA to the basal diet did not affect dry matter (DM) intake, milk production, sulfur balance, and nitrogen balance. When compared to the basal diet, the addition of sulfates increased the DM digestibility from 67.0 to 69.4%, the sulfur retention from 1.0 to 5.4 g per day, and the apparent sulfur digestibility from 47.7 to 66.6%. The substitution of 4 g of sulfur per day from sulfates with an equivalent amount of sulfur from MHA decreased DM intake from 19.4 to 17.6 kg per day, but increased fat level in milk from 3.4 to 3.7%. Fat corrected milk yield was the same for all treatments. In a comparative study involving 40 lactating cows and 121 balance trials, DM digestibility became maximal at about 0.15% sulfur in the total diet when sodium sulfate, calcium sulfate, magnesium sulfate, and potassium sulfate were used as supplements, and about 0.18% sulfur when MHA was used. Raising the sulfur concentration from 0.05 to 0.12% in the total diet brought lactating cows into slightly positive sulfur balance when they were depositing 4–9 g per day of sulfur in the milk. It was concluded that supplemental inorganic sulfur from sodium, calcium, potassium, and magnesium sulfates sustained optimum utilization of sulfur when fed in the diet at 0.20% sulfur (53 mg per kg body weight per day) to cows producing as much as 35 kg of milk per day. Higher concentrations of sulfur intake did not have any effect on nitrogen, sulfur and DM digestibility, but concentrations of 0.35% sulfur and above in the ration (70–90 mg per kg body weight per day) were associated with diminished DM intakes.