Effects of soybean meal treated with tannins extracted from pistachio hulls on performance, ruminal fermentation, blood metabolites and nutrient digestion of Holstein bulls

•We evaluated treated soybean meal with tannins extracted from pistachio hulls.•Tannins decreased ruminal NH3-N concentration and protozoa population of Holstein bulls.•Treated soybean meal could improve growth performance of young bulls.

This experiment was conducted to study the effects of soybean meal (SBM) treated with various amounts of tannins extracted from pistachio hulls on performance, ruminal fermentation, nutrient digestibility, and blood metabolites in Holstein bulls. Twenty-eight Holstein bull calves (256 ± 63 kg body weight) were randomly assigned to one of four dietary treatments for 14 weeks. Each treatment group received one of four SBM treatments included in a total mixed ration (TMR) at a constant rate of 105 g/kg DM. Soybean meal was treated with pistachio extract concentrate (PEC), which contained 111.4 g/kg total phenol and 71.3 g/kg total tannin per dry matter of extract, at four experimental treatment rates of 0 (SBM-0), 5 (SBM-5), 10 (SBM-10), and 15 (SBM-15) kg PEC per 100 kg SBM on a dry matter basis. Blood samples were collected monthly and ruminal fluid samples were collected on d 83 and d 85 of treatment. Treatment of SBM with PEC did not affect final body weight or dry matter intake (DMI), but adding PEC linearly increased average daily gain (L, P=0.001) and feed efficiency (L, P=0.001). Inclusion of PEC linearly decreased ruminal ammonia nitrogen (L, P=0.02) and total protozoal population (L, P=0.002), but did not affect concentrations of total volatile fatty acids (VFA), individual VFA or pH in the rumen. Total tract nutrient digestibility and blood metabolites were unaffected by SBM treatment with PEC, except for concentrations of albumin and total protein in plasma, which increased linearly (L, P=0.004 and P=0.001, respectively) with increasing PEC treatment. These results suggest that PEC supplementation decreases ruminal ammonia nitrogen concentration and total protozoa population and improves growth performance of Holstein bulls.