Effects of Live Yeast Supplementation on Growth Performance and Biomarkers of Metabolism and Inflammation in Finishing Pigs during Heat Stress

Study objectives were to determine the effects of live yeast supplementation (ActisafHR+; 0.25g/kg; Phileo-Lesaffre, Milwaukee, WI) on growth performance and biomarkers of metabolism and inflammation in heat-stressed and nutrient-restricted pigs. Crossbred barrows (n = 96; 80 ± 1 kg BW) were blocked by initial BW and randomly assigned to one of six dietary-environmental treatments: 1) thermoneutral (TN) ad libitum control diet (TNCtl), 2) TN ad libitum yeast diet (TNYst), 3) TN pair-fed (PF) control diet (PFCtl), 4) TN PF yeast diet (PFYst), 5) heat stress (HS) ad libitum control diet (HSCtl), and 6) HS ad libitum yeast diet (HSYst). The study consisted of three experimental periods (P): during P0 (5 d), all pigs were housed in TN conditions (20.23 ± 0.01°C, 57.2 ± 0.3% RH) and fed the control diet ad libitum. During P1 (7 d), pigs were fed their respective dietary treatments and kept in TN conditions. During P2 (28 d) HSCtl and HSYst pigs were exposed to progressive cyclical HS conditions (28 to 33˚C, 37.8 ± 0.2% RH), while TNCtl, TNYst, PFCtl, and PFYst pigs remained in TN conditions and were fed ad libitum or pair-fed to their HSCtl and HSYst counterparts. Pigs exposed to HS had an overall increase in rectal temperature, skin temperature, and respiration rate (0.3˚C, 5.5˚C, and 23 bpm, respectively; P < 0.01) compared to TN pigs. ADFI decreased in HS compared to TN pigs (~1kg, 30%; P < 0.01). Similarly, ADG and final BW decreased in HS relative to TN pigs (26 and 7%, respectively; P < 0.01); however, no differences in G:F were observed between HS and TN treatments (P = 0.16). Under TN conditions, a tendency for decreased ADFI and increased G:F was observed in TNYst relative to TNCtl pigs (P < 0.10). Despite marked differences in ADFI, circulating insulin was similar between HS and TN pigs (P = 0.42). Additionally, HS pigs tended to have decreased plasma NEFA relative to their TN counterparts (~22%; P = 0.07). Circulating triiodothyronine (T₃) and thyroxine (T₄) were decreased in HS compared to TN treatments (~19 and 20%, respectively; P < 0.05). Circulating TNFα did not differ across treatments (P = 0.57); however, a tendency for decreased TNFα levels (P = 0.09) was observed in HSYst relative to HSCtl pigs. In summary, live yeast supplementation tended to improve feed efficiency under TN conditions and reduced inflammation during HS.