The effects of zinc amino acid complex on biomarkers of gut integrity, inflammation, and metabolism in heat-stressed ruminants

摘要

Study objectives were to evaluate the effects of replacing40 mg/kg of dietary Zn from Zn sulfate (ZS)with Zn amino acid complex (ZA; Zinpro Corporation,Eden Prairie, MN) on inflammation and intestinal integrityin heat-stressed and pair-fed (PF) ruminants.Forty Holstein steers (173.6 ± 4.9 kg) were randomlyassigned to 1 of 5 dietary-environmental treatments:(1) thermoneutral (TN) ad libitum with 75 mg/kg ofdry matter (DM) ZS (ZSCON); (2) TN pair-fed with75 mg/kg DM ZS (ZSPF); (3) TN pair-fed with 40 mg/kg DM ZA and 35 mg/kg DM ZS (ZAPF); (4) heatstress (HS) ad libitum with 75 mg/kg DM ZS (ZSHS);and (5) HS ad libitum 40 mg/kg DM ZA and 35 mg/kg DM ZS (ZAHS). Before study initiation, calveswere fed their respective diets for 21 d. Following thepre-feeding phase, steers were transferred into environmentalchambers and were subjected to 2 successiveexperimental periods. During period 1 (5 d), all steerswere fed their respective diets ad libitum and housedin TN conditions (20.2 ± 1.4°C, 30.4 ± 4.3% relativehumidity). During period 2 (6 d), ZSHS and ZAHSsteers were exposed to cyclical HS conditions (27.1 ±1.5°C to 35.0 ± 2.9°C, 19.3 ± 3.5% relative humidity),whereas the ZSCON, ZSPF, and ZAPF steers remainedin TN conditions and were fed ad libitum or pair-fedrelative to their ZSHS and ZAHS counterparts. Overall,steers exposed to HS had markedly increased rectaltemperature (0.83°C), respiration rate (26 breaths permin), and skin temperature (8.00°C) relative to TNtreatments. Rectal temperature from ZAHS steers wasdecreased (0.24°C) on d 4 to 6 of HS relative to ZSHSsteers. Regardless of diet, HS decreased DMI (18%)relative to ZSCON steers. Circulating glucose fromHS and PF steers decreased (16%) relative to ZSCONsteers. Heat stress and nutrient restriction increasedcirculating nonesterified fatty acids 2- and 3-fold, respectively,compared with ZSCON steers. Serum amyloidA increased ~2-fold in PF relative to ZSCON andHS steers. We detected no treatment effect on bloodpH; however, ZAHS steers had increased HCO_3 relativeto ZSHS. Relative to ZSHS, ZAHS steers had increasedjejunum villi height (25%), a tendency for increasedileum villi height (9%), and decreased duodenal villiwidth (16%). In summary, ZA supplementation hassome beneficial effects on thermal indices, intestinalarchitecture characteristics, and biomarkers of leakygut in heat-stressed steers, indicative of an amelioratedheat load, and thus may be a nutritional strategy tominimize negative consequences of HS.