Regulating effects and mechanisms of Chinese medicine decoction on growth and gut hormone expression in heat stressed pigs

Exposure to high temperatures during the summer renders pigs susceptible to severe heat stress. Our previous studies found that pig small intestine epithelial tissue became significantly damaged following exposure to heat stress, negatively affecting body weight gain. The deleterious effects of heat stress could be ameliorated using a traditional Chinese medicine decoction (CMD), sustaining normal growth while under heat stress. In the current study, we hypothesized the mechanism of CMD activity to be via regulation of gut hormones (NPY, MLN, SCT and GCG) secretion from endocrine cells, which are responsible for nutrient digestion and absorption. To test this, 36 Chinese experimental mini-pigs (2 months of age) were screened according to weight and litter origin, and divided into three treatment groups: control (23 °C for 24 h + standard feed), heat stress (HS; 26 °C for 19 h, 40 °C for 5 h + standard feed) and CMD (26 °C for 19 h, 40 °C for 5 h + standard feed supplemented with CMD); n = 12 per group. Feed intake and body weight gain were measured daily. Pigs were euthanized at days 1 and 6 after initial treatment with blood and sections of small intestine epithelial tissue collected. Serum cortisol (Cor) concentrations were determined using RIA. Endocrine cell number and structural analysis were performed using silver staining, and gut hormone secretion examined by microarray. Dietary supplementation with CMD significantly improved porcine growth performance (P < 0.05), decreased the Cor levels (P < 0.01), increased endocrine cell number as well as up-regulating neuropeptide Y (NPY), motilin (MLN) and secretin (SCT) and down-regulating glucagon (GCG) expression in pig jejunum on day 6 when compared with the HS group. Taken together, our results indicate CMD supplementation can significantly reduce the negative effects of heat stress on pig jejunum, maintaining growth performance similar to non-heat stressed animals. CMD's activity appears to be via adjusting gut hormone secretion to regulate metabolism and improve animal growth.