LAUSR

Abstract This study compared the effects of supplementation of postnatal Holstein dairy calves with low doses of zinc-methionine (Zn-Met) or zinc oxide (ZnO) on growth performance, diarrhea incidence, and the integrity of the small intestinal epithelial barrier. Twenty-four male newborn Holstein dairy calves with similar body weight (42.0 ± 1.2 kg) received raw milk and starter containing zinc at 4.05 mg/kg and 176 mg/kg dry matter, respectively. All animals were randomly allocated to one of three groups (n = 8 per group): a control group (CON, without extra zinc supplementation), a Zn-Met group (receiving 455 mg of Zn-Met per day, equivalent to 80 mg of zinc per day), or a ZnO group (receiving 103 mg of ZnO per day, equivalent to 80 mg of zinc per day). The experiment lasted for 14 days. Zn-Met and ZnO were mixed with milk and fed to the calves. Body weight, height, length, and heart girth were measured on the morning of days 1, 7, and 15. Feed intake and fecal scores were recorded daily during the experimental period. Blood samples were collected on day 15 before morning feeding. Thereafter, the animals were euthanized and their small intestines were collected for examination of intestinal morphology and the expression levels of mRNAs encoding jejunal mucosal tight junction (TJ) proteins. The two different sources of zinc did not influence growth performance or diarrhea incidence in dairy calves during days 1–7 or 1–14 after birth. However, Zn-Met supplementation reduced the diarrhea incidence (35.7 % [Zn-Met] vs. 58.9 % [CON]) and improved the average daily gain (ADG) (500 g/d [Zn-Met] vs. 422 g/d [CON]) and feed efficiency (feed-to-gain ratio: 2.05 [Zn-Met] vs. 2.47 [CON]) significantly during the second week after birth (P