Effect of alkali pretreatment of wheat straw on the efficacy of exogenous fibrolytic enzymes.

The effects of pretreating wheat straw with alkali on the efficacy of exogenous fibrolytic enzymes for improving straw digestibility were studied in vitro, in situ, and in vivo. In Exp. 1, untreated straw (US); alkali-treated (5% NaOH, wt/wt) straw (AS); and autoclaved, alkali-treated straw (AAS) were sprayed with 0 or 1.5 mg/g DM of enzyme mix (xylanase, beta-glucanase, carboxymethylcellulase, and amylase) and incubated for 30 h in buffered ruminal fluid (3 x 2 factorial arrangement). Enzymes increased (P < 0.001) gas production and the incorporation of 15N into microbial N at 4 h, more so with AS or AAS than with US (P < 0.001 for gas; P < 0.05 for 15N). In Exp. 2, US and AS were sprayed with enzymes at 0, 0.15, or 1.5 mg/g DM (2 x 3 factorial) and incubated ruminally in nylon bags for up to 80 h to determine the in situ DM disappearance (ISDMD). Interactive effects (P < 0.05) of pretreatment and enzymes were observed on all ruminal degradation parameters. Alkali increased the rate (P < 0.01) and extent (P < 0.001) of ISDMD irrespective of enzymes. Enzymes applied to US did not affect the extent of ISDMD, but they increased (P < 0.01) the extent of ISDMD when applied to AS. Substrates from Exp. 1 and 2 were incubated in acetate buffer for 24 h to measure the hydrolytic loss of DM and release of reducing sugars and phenolic compounds. Alkali pretreatment and enzymes each increased (P < 0.001) DM loss and the release of reducing sugars and, in combination, exerted synergistic effects (P < 0.001). Enzymes did not affect the release of phenolic compounds from the straw. In Exp. 3, total-tract digestibility of untreated and enzyme-treated (100 mL/kg DM) ammoniated straw was assessed using 32 beef cows in eight pens. Wrapped straw bales were injected with NH3 (3% [wt/wt], DM basis) 4 mo before the study; enzymes were applied immediately before feeding. Applying enzyme to ammoniated straw increased (P < 0.05) digestibilities of DM, OM, and total N but did not affect the intake of DM or digestibility of ADF. Pretreatment of straw with alkali enhanced the efficacy of exogenous enzymes, presumably by breaking esterified bonds and releasing phenolic compounds and/or by swelling the crystalline cellulose and enhancing enzyme penetration. Including enzymes that mimic alkali hydrolysis (e.g., esterases) in commercial feed additives could substantially improve the value of these products for ruminants.

Internal parasites of Washington cattle.

The occurrence of internal parasites in Washinton cattle was estimated. During the survey period in 1972 and 1973, more than 3,700 fecal samples from 29 herds and 4 feedlots, and viscera from 55 cattle were examined. The percentage of fecal samples with parasite eggs or oocysts from herds was as follows: oocysts, 77%; "strongyline" eggs, 44%; Nematodirus eggs, 3%; Moniezia eggs, 3%; Fasciola eggs, 2%; Trichuris eggs, 2%; and Dictyocaulus larvae, 1%. The fecal samples from feedlots contained principally strongyline eggs which varied markedly in numbers among groups of cattle in the lots. The predominant parasite in viscera was Ostertagia spp, which was recovered from all of the cattle examined. Other parasites identified in the survey were found less frequently in these examinations. Cattle in dairy and beef operations utilizing irrigated pastures were particularly prone to Fasciola infections, and more strongyline eggs were observed there than in fecal samples from other management systems. Seasonal fluctuations in numbers of strongyline and Fasciola eggs were pronounced.