EFFECTS ON NUTRIENT DIGESTION OF WHEAT PROCESSING AND METHOD OF TALLOW ADDITION TO THE DIETS OF LACTATING DAIRY-COWS

Five multiparous Holstein cows in midlactation that were fitted with r uminal and duodenal cannulas were used in a 3 x 5 incomplete Latin squ are. The objective of this study was to examine the effects on nutrien t digestion of wheat processing and method of tallow addition to the d iets of lactating dairy cows. Diets consisted of 45% forage and 55% co ncentrate, and each diet contained 20% wheat and 2% tallow (as-fed bas is). Treatments were dry-rolled wheat with tallow added to the concent rate, steam-rolled wheat with tallow added to the concentrate, and ste am-rolled wheat with tallow added first to the wheat. The dry matter i ntake; digestion of starch, fiber, and fatty acids; ammonia N concentr ation; and molar proportions of volatile fatty acids in ruminal fluid were not affected by treatments. The apparent digestibility in the tot al tract of organic matter and nitrogenous compounds was significantly higher for the steam-rolled treatment with tallow added first to the wheat. Mean ruminal fluid pH was similar across treatments; however, c ows fed the diet containing steam-rolled wheat with tallow added first to the wheat had the smallest pH change from 0 to 2 h postfeeding. Mi lk yield did not differ, regardless of cow diet. Method of tallow addi tion had marked effects on the apparent digestibility of organic matte r and N in the total tract of lactating dairy cows.