Effects of Zinc Amino Acid Complex on Biomarkers of Gut Integrity and Metabolism during Heat Stress and a Following Recovery Period in Growing Pigs

Study objectives were to determine the effects of zinc amino acid complex (ZnAA, Zinpro Corporation, Eden Prairie, MN) on metabolism, biomarkers of leaky gut and inflammation in heat-stressed and nutrient-restricted pigs. Crossbred gilts (n=50; 50 ± 2 kg BW) were blocked by initial BW and randomly assigned to one of five treatments: 1) thermoneutral (TN) ad-libitum control diet (TNCtl), 2) TN pair-fed control diet (PFCtl), 3) TN pair-fed zinc diet (PFZn), 4) heat stress (HS) ad-libitum control diet (HSCtl) and 5) HS ad-libitum zinc diet (HSZn). The study consisted of three experimental periods (P): during P1 (7d), all pigs were fed their respective diets ad-libitum and housed in TN conditions (20.84 ± 0.03˚C, 47.11 ± 0.42% RH). During P2 (7d), HSCtl and HSZn pigs were exposed to progressive cyclical heat stress conditions (27 to 30˚C, 41.9 ± 0.5% RH), while the TNCtl, PFCtl and PFZn pigs remained in TN conditions and were fed ad-libitum or pair-fed to their HSCtl and HSZn counterparts. During P3 (7d), all pigs were kept in TN conditions and fed ad-libitum. Pigs exposed to HS had an overall increased rectal temperature, skin temperature and respiration rate (0.33°C, 3.76°C and 27 bpm, respectively; P<0.01). HS decreased ADFI and ADG relative to TN controls (1.79 vs. 2.48 kg/d and 0.60 vs. 0.92 kg, respectively, P<0.05) but these variables were unaffected by dietary treatment. Circulating insulin levels were decreased in the PF relative to TN and HS pigs (P=0.03), and plasma NEFA levels were increased in Zn relative to Ctl-fed pigs (P=0.03). During recovery, no differences were observed in rectal temperature or respiration rate across treatments, but HSZn pigs had decreased skin temperature relative to TN, PF and HSCtl pigs (P<0.01). During P3, no effects of ZnAA were observed in production parameters, however, PF pigs had increased ADFI and ADG relative to TN and HS treatments (P<0.01). During P3, circulating insulin levels were increased in pigs that were in HS relative to TN and PF pigs (75%, P<0.05); furthermore, blood glucose tended to be increased in Zn relative to Ctl-fed pigs (P=0.07). Interestingly, plasma TNFα levels tended to be decreased during P1 (P=0.08) and were decreased during P3 (P=0.04) in Zn relative to Ctl-fed pigs. Circulating lipopolysaccharide binding protein was not different among periods (P>0.10). In summary, ZnAA appeared to reduce TNFα (regardless of HS) and the stimulatory effect of HS on insulin secretion is amplified during HS recovery.