Akt expression and lactose synthesis during heat exposure in Saanen goat

Abstract

In tropical countries, high ambient temperature (HTa) is a fundamental factor that cause a decline in the mammary gland function in dairy animals. Dairy animals fed under HTa decreased milk yield (MY) as well as milk compositions. The current study focuses on the effect of HTa to decrease milk synthesis from natural and in vitro HTa condition. The first experiment was performed to investigate the effect of HTa from the natural condition in early lactating Saanen goat, 2-4 weeks of postpartum (2 PP-4 PP). Five animals were investigated during the winter season as control ambient condition. Six animals as the natural HTa group was conducted during summer. The environmental conditions, rectal temperature (Tr), respiratory rate (RR), dry matter intake (DMI) and MY were measured everyday throughout the experiment. At the end of 2 PP and 3 PP, blood and milk samples were collected to measure blood glucose, oxidative stress status, and milk composition. In addition, the milk cells were isolated from milk sample to evaluate gene expression. The second experiment was performed using mammary epithelial cells (MECs) culture isolated from goat milk to investigate the effect of HTa on lactose synthesis and oxidative stress status of MECs culture. The cells were allocated into two temperature groups that were 37 ºC as the control and 39 ºC as the HTa group. After 1- and 48-hour incubation the culture medium was collected for measured lactose concentration and MECs were harvested to determine gene expression, respectively. In the first experiment, the average ambient temperature (Ta), relative humidity (RH), temperature humidity index (THI), and RR were significantly increased in summer when compared with the winter season. In both seasons Tr in the afternoon and evening was significantly higher than that in the morning. However, Tr from summer was not significantly different from winter. Whereas, DMI and MY during the winter group showed significantly higher than that from the summer group. In the present study, during summer, plasma glutathione peroxidase (GPx) activity in the afternoon were significantly higher than that in winter. Whereas, plasma cortisol in the afternoon was significantly higher than that in the morning in both seasons. Moreover, the relative gene expressions of α-lactalbumin (α-LA) and heat shock protein 70 (HSP70) gene were higher in summer when compared with the winter season. However, there were no differences between the season on the relative expression of β-1,4-galactosyltransferase (β-GALT1) and Akt genes. The results suggested that the natural ambient condition from the present experiment showed high temperature and humidity index especially during the afternoon in both winter and summer months. The effect of HTa on milk synthesis might be related to an increase in antioxidative capacity of the goats and expression of HSP70 gene but this effect is not related to Akt expression. In the second experiment, the results of the relative gene expression of HSP70 increased significantly after 1 hour HTa incubation when compared with the control. At 1 or 48 hours incubation, HTa condition could not affect β-GALT1 and α-LA genes expression as well as Akt. In addition, there was no difference in lactose concentration between control and HTa group. These results showed that HTa did not influence lactose synthesis gene expression of MECs. In conclusion, the effect of HTa on MY and MECs culture apparently related with increasing expression of HSP70 from both natural and in vitro study. However, HTa did not affect the expression of β-GALT1, α-LA and Akt genes.