Dietary Polyethylene Glycol Mitigates Tannin-Related Constraints and Enhances Performance in Growing Balkhi Sheep Fed Oak Leaf-Based Diets.

In hilly regions of Pakistan, particularly South Waziristan, oak (Quercus baloot) leaves are a potential locally available feed source, but their tannins may reduce intake and nutrient digestion. Because polyethylene glycol (PEG) binds dietary tannins and can reduce tannin-protein and tannin-enzyme interactions, potentially improving nutrient availability, we evaluated PEG as a practical dietary additive in tannin-rich oak diets. Using practical, non-purified diets, we conducted a 60-day study with thirty-two male Balkhi sheep (3 months old; initial body weight 21.20 ± 0.29 kg). Sheep were stratified by weight and allocated to four diets in a 2 × 2 factorial design: 0% oak + 0% PEG, 45% oak + 0% PEG, 0% oak + 2% PEG, and 45% oak + 2% PEG. We evaluated dry matter and nutrient intake, apparent digestibility, body weight gain, hematology, and blood biochemistry. The 45% oak + 2% PEG diet produced the highest nutrient intake, digestibility, final body weight, and average daily gain, and the lowest Feed conversion ratio. Compared with the 45% oak + 0% PEG diet, average daily gain increased from 77.3 to 181.8 g/day, and dry matter digestibility increased from 41.9% to 57.2%. Endpoint hematology showed no treatment-related abnormalities, while blood urea nitrogen and alanine aminotransferase were significantly lower in sheep receiving 45% oak + 2% PEG than in those receiving the other three diets. Because the diets were practical formulations rather than nutrient-matched mechanistic diets, these findings support the tested oak + PEG diet under local study conditions but do not isolate tannin binding as the sole mechanism.