Evaluation of wood chips and rice hulls as alternative fiber sources in rations self-fed to early-weaned calves

Two experiments were conducted to evaluate the merit of wood chips (WCH, Exp. 1) or rice hulls (RH, Exp. 2) as the sole fiber source in a high-concentrate diet fed to early-weaned calves as well as their method of delivery (hand-feeding versus self-feeder). Rations were formulated to contain similar concentrations of N, energy and NDF and were offered ad libitum. In Exp. 1, 36 Hereford calves (84.4 kg SE 4.5) were randomly allocated to nine pens and one of three dietary treatments: (1) 160 g/kg of sorghum silage (SS) and 800 g/kg of concentrate hand-fed, 2) 80 g/kg of WCH and 920 g/kg concentrate hand-fed, and (3) same ration as in (2) but self-fed. In Exp. 2, 36 early-weaned Hereford calves (97.4 kg SE 1.7) blocked by BW were randomly allocated to nine pens and one of three dietary treatments: (1) 200 g/kg of alfalfa hay (AH) plus 800 g/kg of concentrate hand-fed, (2) 80 g/kg of RH plus 920 g/kg of concentrate hand-fed, and (3) same ration as in 2) but self-fed. In both experiments animals were weighed (BW) every 14 days, dry matter intake (DMI) was measured weekly, and daytime animal behavior was observed. Gain-to-feed ratio (GF), NEg and a sorting index to characterize the selective consumption of specific fractions, were calculated. Data were analyzed according to a randomized complete plot (Exp. 1) or block (Exp. 2) design, with repeated measures. Fiber source and delivery method effects were tested through orthogonal contrasts. In Exp. 1, replacing SS with WCH did not affect body BW gain, DMI, GF, or NEg. No differences were observed either in feed sorting or eating activity (EA). Using a self-feeder to deliver the WCH ration reduced EA (P < 0.05), without affect GF. In Exp. 2, replacing AH with RH did not affect BW gain or DMI but it improved GF (P < 0.05). Higher sorting against large particles (>8 mm) and ADF were observed for AH compared to RH (P < 0.05). Using a self-feeder to deliver the RH ration reduced DMI and EA (P < 0.05) without affecting BW gain and improving GF (P = 0.01) compared to hand-feeding. Also, it increased selective refusal of ADF (P < 0.05) but not of NDF, without affecting rumination. Treatments did not affect peNDF supply. Results from both experiments show the viability of the use of WCH and RH as a source of fiber in high-concentrate rations for early-weaned calves, as well as their suitability for delivery in self-feeders.