Nutritive value and in situ digestibility of pearl millet hay as affected by moisture concentration and bale sampling depth

Seven hectares (ha) of pearl millet [Pennisetum glaucum (L.) R. Br.] were divided into 3 blocks with 3 whole plots each to evaluate the effects of moisture (165, 187, and 274 g/kg of DM) and sampling depth (0.2, 0.4, and 0.6 m) in round bales on chemical composition and in situ disappearance. Plots were assigned randomly to moisture treatments. Round bales (n = 3 per plot; 1.2 × 1.5 m, 568 kg) were obtained and sampled at 3 different depths within each bale (n = 81) before and after 71 d of storage. Duplicate in situ bags (10 × 20 cm) were incubated in 6 ruminally cannulated cows (BW = 585 ± 37.8 kg) up to 120 h. Residual DM for each sampling time was fit to a nonlinear model using PROC NLIN of SAS to determine DM degradation kinetics. Data were analyzed as a split-plot design using Proc Mixed procedures of SAS and tested for moisture, depth, and their interactions. Bale temperature and concentrations of ADL were greater (P < 0.05), whereas hemicellulose concentrations and the rate of DM disappearance (Kd) were reduced (P < 0.05) in pearl millet baled at 274 g/kg of DM. Sampling depth did not affect (P > 0.10) any of the digestion variables, but the water-soluble fraction, potentially degradable fraction, and effective ruminal disappearance as well as concentrations of OM, NDF, and acid-detergent insoluble nitrogen were affected (P < 0.05) by the moisture × sampling depth interaction. Therefore, a greater range in sampling depth should be used to accurately assess heat damage in large round bales.