Whole corn grain-based diet and levels of physically effective neutral detergent fiber from forage (pefNDF) for feedlot lambs: Digestibility, ruminal fermentation, nitrogen balance and ruminal pH

The present study evaluates the increasing levels of physically effective neutral detergent fiber of forage (ₚₑfNDF) in a whole corn grain-based diet on DMI, the apparent digestibility of nutrients, the nitrogen balance, and ruminal fermentation. Thirty ruminally cannulated Dorper × Santa Inês ram lambs, castrated, with 30.14 ± 3.01 kg of initial BW and approximately 3-month-old were used. The experimental design was in a randomized complete block (5 treatments and 6 blocks), defined by BW and age at the beginning of the experiment. The experimental diets were: CONT (positive control) – ground corn-based diet with 72 g/kg of ₚₑfNDF; 0ₚₑfNDF – whole corn grain-based diet without forage; 36ₚₑfNDF – whole corn grain-based diet with 36 g/kg of ₚₑfNDF; 72ₚₑfNDF – whole corn grain-based diet with 72 g/kg of ₚₑfNDF; 108ₚₑfNDF – whole corn grain-based diet with 108 g/kg of ₚₑfNDF (DM basis). The experimental diets were formulated to be isonitrogenous. The treatments did not affect the DMI. The increasing levels of ₚₑfNDF decreased the digestibility of DM, OM (P = 0.03) and TDN (P < 0.001). Whole corn grain-based diets associated or not with ₚₑfNDF showed higher digestibility of DM and OM (P < 0.01) than CONT. On the other hand, 0ₚₑfNDF showed higher digestibility of TDN (P < 0.01) than CONT. Ruminal propionate concentration of lambs fed CONT was lower than 0ₚₑfNDF (P = 0.04), while the isobutyrate concentration was higher (P = 0.01) for lambs on the CONT compared to lambs that received the other diets. The CONT had a lower ruminal pH (hour 9, P = 0.04; hour 12, P < 0.01) and ruminal pH area under the curve (hour 9, P = 0.03; hour 12, P < 0.02) when compared to the 0ₚₑfNDF. Additionally, at hours 9 (P < 0.02), 12 (P < 0.001) and 16 (P = 0.001) the lambs of the CONT had lower ruminal pH and pH area under the curve compared to lambs fed diets with whole corn with ₚₑfNDF. At hour 24, there was a linear increase in ruminal pH (P = 0.02) and ruminal pH area under the curve (P < 0.01) according to the increase in ₚₑfNDF levels in the diets. In diets with whole corn, the addition of ₚₑfNDF is not recommended, considering that no benefits were observed for nutrient digestibility, ruminal fermentation or nitrogen balance. The diet consisting of whole corn proved to be suitable for finishing lambs, as it enhanced DM and OM digestibility without clinical evidence of ruminal acidosis.