Ben‐Ghedalia, D., Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan, Israel
Shefet, G., Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan, Israel
Miron, J., Institute of Animal Science, Agricultural Research Organization, Volcani Center, PO Box 6, Bet Dagan, Israel

Cotton straw (CS) was treated with ozone, ammonium hydroxide and a combination of the two, and the effect of the treatments on the composition of cell wall (CW) fractions and on in vitro organic matter digestibility (OMD) was studied. The ammonium hydroxide treatment did not affect the lignin content, but a reduction of 50% in lignin and hemicellulose, and a corresponding increase in cell contents, were found in the ozone‐treated materials. The pH of CS was reduced from 6.11 to 2.28 by ozone, probably due to the formation of organic acids derived from the oxidised lignin. Plateau‐like ultraviolet (u.v.) spectra of the water extracts were obtained with all the treatments indicating that a variety of u.v. absorbing substances, including phenolic components, have been released. The extinction at 280 nm, suggested to indicate the concentration of phenolic components, was increased compared to the untreated CS by 37 and 98% with the ozone and the combined treatment, respectively; the ammonium hydroxide treatment had little effect. In vitro OMD was significantly increased by more than 100% by the ozone treatments, as a result of the partial conversion of cell walls into cell contents and the increased degradation of the CW. Ozone treatments increased the initial rate of in vitro OMD. Copyright © 1980 John Wiley & Sons, Ltd