Effect of increasing levels of physically effective neutral detergent fibre on growth performance, feeding behaviour, and carcasses and gut characteristics of feedlot lambs fed ground corn

The present study evaluated the effect of increasing levels of forage physically effective neutral detergent fiber ( pef NDF) on performance of feedlot lambs fed ground corn-based diets. The experimental design was a randomized complete block (grouping 6 treatments into 10 blocks), defined by initial BW and age at the beginning of the experiment. The experimental treatments were defined by the inclusion of forage pef NDF at 0 (0 pef NDF); 26 (26 pef NDF); 52 (52 pef NDF); 78 (78 pef NDF); 104 (104 pef NDF) and 130 (130 pef NDF) g/kg DM of a flint corn-based diet. The source of the forage was coast cross ( Cynodon sp. ) hay. There was a quadratic effect for dry matter intake [DMI (kg/d; P = 0.03)] and average daily gain [ADG (P < 0.01)], peaking at 78 pef NDF. However, the feed efficiency (FE) decreased linearly (P = 0.03) with increasing pef NDF levels. Intake time increased linearly (P < 0.001), but rumination (P < 0.0001) and chewing times (min/d) (P < 0.001) showed a quadratic effect, with the greatest values observed at 78 pef NDF when expressed in min/g DM. The slaughter body weight (SBW) showed a quadratic effect (P < 0.01), with the greatest values observed for 78 pef NDF. However, the greatest (P < 0.01) hot carcass weight (HCW) and hot carcass yield (HCY) were observed for lambs fed a diet 52 pef NDF. Diets containing ground flint corn as the main energy source for feedlot lambs can be formulated with smaller pef NDF levels than found in the literature, from 52 to 78 g/kg DM of pef NDF, depending on the objective. • Intake and daily gain peaked at 78 g/kg of effective forage fiber in the diet of lambs. • Feed efficiency decreased linearly as the effective forage fiber level increased. • Rumination and chewing times were greatest at 78 g/kg of effective forage fiber. • Carcass weight and yield were maximized at 52 g/kg of effective forage fiber. • Optimal forage fiber is 52-78 g/kg to balance animal gain and carcass yield.