LAUSR

Abstract This study was to evaluate impacts of zinc sulfate (ZS) and coated ZS (CZS) supplementation on milk performance, nutrient digestibility and rumen fermentation. Forty-five Holstein dairy cows were assigned in a randomized block design to one of five treatments: control, ZS supplementation (30 mg Zn/kg dry matter [DM] as ZS) or CZS supplementation (10, 20 and 30 mg Zn/kg DM as CZS for LCZS, MCZS and HCZS, respectively). The experiment lasted for 110 days with 20 days for adaptation and 90 days for data collection. When comparing Zn source at same supplemental level (30 mg Zn/kg DM), milk yield and total-tract digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) tended to be higher and ruminal activities of xylanase, cellobiase, pectinase and protease and serum alkaline phosphatase (ALP) were higher for HCZS than for ZS. Increasing CZS addition linearly increased DM intake and yields of milk, milk fat and milk protein but did not affect milk lactose yield, milk composition content and feed efficiency. Digestibility of DM, organic matter, crude protein, NDF and ADF, ruminal total volatile fatty acids content and acetate to propionate ratio linearly increased but ammonia N content linearly decreased with increasing CZS addition. Quadratic responses were observed for proportions of acetate and propionate. Activities of cellulase and protease and populations of total bacteria, fungi, protozoa, dominant cellulolytic and amylolytic (proteolytic) bacteria responded linearly and positively with increasing CZS addition. Increasing CZS addition linearly increased liver Zn and blood total protein, albumin, ALP and Zn. Results indicated that CZS could be used as a Zn supplement in cows, and supplementing 20 or 30 mg/kg DM of Zn from CZS stimulated performance, nutrients digestion and ruminal fermentation and improved Zn status in cows fed diets containing 31.2 mg Zn/kg DM.