In vitro first order dry matter disappearance kinetics of chemically and physically treated cottonseed hulls

Abstract

Introduction Limited supplies and or high costs of conventional roughages and concentrates dictate that alternate sources of feeds should be used in ruminant rations (Brown et al., 1976). Cottonseed hulls (CH) are a by-product of cotton processing, containing a large proportion of neutral detergent fibre (NDF) and associated lignin, and have been considered as a useful non-forage fibre source in ruminant rations (Hall and Akinyode, 2000). However, low dry matter (DM) digestibility of CH is an inhibitory factor to include this feedstuff in the high performance dairy cow diets (Brown et al, 1976). Results of previous in vitro studies have revealed that sodium hydroxide treatment of fibrous feedstuffs can improve DM or NDF digestibility of them. The objective of this study was to determine the effect of chemical, using sodium hydroxide, or physical treatment, using microwave irradiation, on in vitro DM disappearance kinetics of CH.Material and methods For chemical treatment, CH were treated with NaOH as 20 g/kg DM [a 20% solution of NaOH was sprayed on CH and kept for 0.5 h (CH2S0.5) or 48 h (CH2S48)] or 40 g/kg DM [a 40% solution of NaOH was sprayed on CH and kept for 0.5 h (CH4S0.5) or 48 h (CH4S48) at room temperature]. Physical processing was done using microwave irradiation (900 W) for 4, 6 and 8 min (CHm4, CHm6, CHm8, respectively). Samples were incubated in a medium prepared as described by Arroquy et al. (2005). Forty-five ml of medium was supplied into a 100 ml bottle containing 0.45 g DM of each sample (Four replicates per each sample were run). Then, each bottle was inoculated under carbon dioxide with 5 ml of mixed rumen microbes. Rumen fluid was obtained from three sheep (49.5±2.5 kg body weight) fitted by rumen fistulae, before the morning feeding, and immediately strained through four layers of cheesecloth. The animals fed 1 kg/d of DM lucerne hay and 0.3 kg/d DM concentrate (165 g CP/kg DM). The bottles were incubated for 24, 48, 72 and 96 h at 38.6º C. After each time of incubation, bottle contents were filtered through a 42 µm filter, and DM of unfiltered medium was determined. Non-linear first order model was used to estimate the digestion kinetic parameters of DM. The model was D (t) = D (i) .e -kd.t + I ; where, D (t) is residual DM at any time, D (i) is potentially degradable fraction, k d is fractional rate constant of digestion (h -1 ) and I is indigestible fraction.Results Non-linear first order parameters of in vitro DM disappearance of the samples are presented in Table 1. Physical or chemical treatment had no significant effect on DM disappearance parameters of CH. Table1 Non-linear first order parameters of in vitro DM disappearance of non treated or chemically and physically treated cottonseed hulls Treatments Parameters CH CH2S0.5 CH2S48 CH4S0.5 CH4S48 CHm4 CHm6 CHm8 s.e.m P D i 0.310 0.310 0.260 0.340 0.350 0.300 0.26 0.290 0.088 P> 0.05 K d 0.007 0.016 0.011 0.006 0.009 0.008 0.011 0.010 0.005 P> 0.05 I 0.140 0.140 0.190 0.110 0.110 0.150 0.190 0.160 0.091 P> 0.05 R 2 0.97 0.93 0.98 ...