Impact of heat stress, nutritional stress and combined (heat and nutritional) stresses on rumen associated fermentation characteristics, histopathology and HSP70 gene expression in goats

ABSTRACT

A study was conducted to assess the impact of heat stress, nutritional stress and combined stresses (heat and nutritional stress) on rumen fermentation characteristics, histopathology of rumen and rumen HSP70 gene expression in goats. Twenty four adult Osmanabadi bucks were divided into four groups, C (n=6; control), HS (n=6; heat stress), NS (n=6; nutritional stress) and CS (n=6; combined stress). The study was conducted for a period of 45 days. The C and HS bucks had ad libitum access to their feed while NS and CS bucks were subjected to restricted feed (30% intake of C bucks) to induce nutritional stress. The HS and CS bucks were exposed to heat stress in an outside environment. Both feed intake and body weight were significantly (p < 0.01) lower in CS and NS groups. The carboxy methyl cellulase activities - extracellular, intracellular and total activity in the rumen fluid differed significantly (p < 0.01) between the groups. The highest concentration of ammonia nitrogen (p < 0.05) was recorded in C while the lowest in the CS group. The concentration of total nitrogen and trichloroacetic acid precipitable N, propionic acid, butyric acid, and valeric acid was lower (p < 0.01) in the restricted fed (NS and CS) bucks as compared to ad libitum fed groups (C and HS). Further, the ratio of acetate to propionate (A P ratio) was also significantly (p < 0.01) higher in CS and NS groups. The higher expression of rumen heat shock protein 70 (HSP70) mRNA was observed in CS goats. The histopathological section of rumen revealed a reduction in the length of rumen villi and thickness in CS, whereas rumen keratinization was highest in the CS group. From the study it can be concluded that when two stresses occur simultaneously, they may have severe impact on rumen fermentation characteristics of bucks.