Lactase activity in steers fed large amounts of dried whole whey.
Large amounts of dried whey (86% of concentrate mix, 60% of total dry matter intake) were fed to four Holstein steers in place of corn and soybean meal in the control diet to evaluate the extent and site of lactose digestion in the ruminant's digestive tract. Diet dry matter was 70% as concentrate mix and 30% as corn silage fed for ad libitum consumption as a total mixed ration. Samples of rumen contents from steers fed dried whole whey contained more butyrate, less propionate, and less ammonia than from steers fed the control diet. Digestibilities of the whey diet were higher for ash and tended to be higher for energy and organic matter and digestibilities of acid detergent fiber and cellulose tended to be lower. Steers were sacrificed at the end of the feeding period, and intestinal tissue, and rumen, intestinal, and cecal contents were sampled for lactase analyses. No lactose was in rumen or small intestine, indicating virtually complete digestion. Lactase activity of intestinal tissue was greatest in the proximal third of the small intestine with little activity in the distal third of the small intestine regardless of diet. Lactase activity per gram tissue protein was similar for both treatment groups throughout the small intestine. Lactase activity of intestinal contents was similar for both treatments; it was greatest in the duodenum and lowest in the ileum and large intestine. Cattle have the capability to consume large amounts of dried whey without digestive disorders or reduced rates of gain.