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A study was conducted to assess the combined effect of heat stress and nutritional
restriction on rumen fermentation characteristics and metabolic activities in Osmanabadi
Bucks. Twenty four adult Osmanabadi bucks (average body weight (BW) 16.0 kg) were used
in the present study. The bucks were divided into four groups viz., 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. C and HS bucks had ad libitum access to their feed while
NS and CS bucks were under restricted feed (30% intake of C bucks) to induce nutritional
stress. The HS and CS bucks were exposed to solar radiation for six hours a day between
10:00 h and 16:00 h to induce heat stress. The data were analyzed using repeated measures
analysis of variance. The carboxy methyl cellulase (CMCase) Extracellular activity (EC),
CMCase Intracellular activity (IC) and CMCase total activity (TA) of rumen liquor 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 CS group. There were significantly (P<0.01)
higher levels of trichloroacetic acid (TCA) in ad libitum (C and HS) fed groups as compared
to restricted fed (NS and CS) groups. There were significantly (P<0.01) higher levels of total
nitrogen in ad libitum (C and HS) fed groups as compared to restricted fed (NS and CS)
groups. There were significantly (P<0.01) higher levels of propionic acid, butyric acid, and
valeric acid in ad libitum (C and HS) fed groups as compared to restricted fed (NS and CS)
groups. Further, the acetate and propionate ratio was significantly (P<0.01) higher in CS and
NS groups as compared to C and HS groups. There were significantly (P<0.01) higher levels
of plasma alkaline phosphatise (ALP) in ad libitum (C and HS) fed groups as compared to
restricted fed (NS and CS) groups. However, plasma Aspartate amino transferase (AST) and
alanine amino transferase (ALT) showed reverse trend (P<0.05) to plasma ALP. The highest
(P<0.01) plasma Triiodothyronine(T3) and Thyroxine(T4) was recorded in C group as
compared to stress groups (HS, NS and CS). Further, the highest leptin concentration was
recorded in C group while the lowest level in CS group. The higher expression of rumen heat
shock protein 70(HSP70) messenger Ribonucleic acid(mRNA) was reported in CS goats.
Further, the higher expression of intestinal HSP70 mRNA was reported in HS goats. The
thyroid alveoli showed significantly lower thyroglobulin activity in HS group. The length of
rumen villi and thickness was reduced more in CS, whereas rumen keratinization was
observed highest in CS group. It can be concluded from this study that when two stressors
occur simultaneously, they may have severe impact on rumen fermentation characteristics
and metabolic activities of bucks as compared to that would occur individually. Further, the
study established the adaptive capability of Osmanabadi bucks to the detrimental effects of
environmental stresses to alter their fermentation and metabolic activities. This is evident
from the significant influences of interaction between treatment and experimental days on
majority of the parameters studied.