Dietary supplementation with tannin and soybean oil on intake, digestibility, feeding behavior, ruminal protozoa and methane emission in sheep

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Tannins and soybean oil are supplements used in diets that depending on concentration may promote beneficial or negative effects on animal productivity. This study aimed to evaluate the effect of supplementation with tannins extract or soybean oil, as well as their combination, on intake, digestibility, methane production, feeding behavior and rumen parameters in Santa Inês crossbred uncastrated male sheep. Eight sheep were assigned to a double 4 × 4 Latin square (4 treatments and 4 periods), and 4 sheep to a simple 4 × 4 Latin square (for ruminal fluid collection) and fed a basal diet of 60% elephant grass and 40% concentrate (dry matter (DM) basis). The treatments were: control (no tannins or soybean oil); tannins (30 g/kg DM); soybean oil (50 g/kg DM); and tannins plus soybean oil (30 g/kg DM of tannin and 50 g/kg DM of soybean oil). Intake did not differ between treatments. Tannins supplementation increased eating time (ET) (P < 0.01) and decreased DM intake rate (DMIR) (P = 0.02) and rumen fluid pH (P = 0.04), but did not affect digestibility. Supplementation with soybean oil decreased acid detergent fibre (P = 0.04) and neutral detergent fibre (NDF) (P = 0.02) digestibility, and increased number (P < 0.05) and time (P = 0.04) of chewing per ruminal bolus. The combination of tannins and soybean oil decreased digestibility of organic matter (DOM) (P = 0.04) and NDF (P = 0.01), increased ET (P < 0.01) and decreased DMIR (P < 0.01) and NDF intake rate (P = 0.02). The inclusion of tannins did not decrease methane production. However, the inclusion of soybean oil or soybean oil plus tannins reduced methane production (absolute value and per unit of ingested DM and digestible organic matter) (P < 0.01). The number of rumen protozoa decreased in the treatments with tannins, soybean oil and soybean oil plus tannins compared to control treatment (P < 0.01), and a greater proportion of reduction was obtained using only soybean oil. The inclusion of soybean oil alone is sufficient to reduce methane production, without affecting DM intake and DOM, although reducing fibre digestion.