Ghrelin, produced mainly in abomasum of ruminants, is a peptide with roles in the regulation of feeding. The present study assessed the alterations of plasma ghrelin in sheep fed with all forage or high-grain rations and the probable effects of altered ghrelin secretion on feed intake in animals with acidic rumen. Eight Karakul male lambs were divided into the control (n = 4) and experiment groups (n = 4) and fed individually for 20 days. The control group was fed an all forage ration for the whole study period. For the experiment group, 40% of the ration was substituted with ground barley for 10 days. For the rest of the study, 62.5% of the ration was substituted with ground barley. Signs of negative alteration of digestive functions (e.g., reduced feed intake, loose manure with reduced dry matter) were observed in the experiment group after day 10 of the experiment when ground barley was increased to 62.5% of the ration. On days 8 and 10 of each step, blood samples were collected for measuring plasma ghrelin level from jugular vein 1 hour before, and 1 and 3 hours after feeding. In the control group, plasma ghrelin increased 1 hour post-feeding (p < 0.05 in step 1) and decreased 3 hours post-feeding. In the experiment group, however, non-significant decreases were noticed in plasma ghrelin concentration 1 hour after feeding, followed by a sharp and significant rise 3 hours post-feeding (p < 0.05). Comparing the control and the experiment groups, we found that plasma ghrelin concentration was lower in the experiment group 1 hour post-feeding with significant difference (P = 0.002) in the second step. At 3 hours post-feeding, plasma ghrelin was higher in the experiment group with significant difference (P = 0.050) in the second step. In conclusion, ration composition may affect ghrelin secretion in sheep. High-grain rations and acidic condition of the rumen may increase ghrelin secretion within a few hours of feeding. This increase in ghrelin secretion, however, may not result in increased feed intake.
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