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.