Weight increase of cotton fiber in an 18% NaOH solution, termed “alkali-centrifuge” or “AC” value, was measured after incubation of either 1 g or 100 mg of the fiber in ruminal fluid. The AC response was a sensitive measure of cellulolytic activity. Thus, fiber incubated at 21 and 51°C exhibited major AC increases even when direct weight losses of the unswollen fiber were less than 2%. Similarly, progressive additions of acetic acid to ruminal fluid progressively depressed both AC response and direct weight loss, but the former was still easily measurable when the latter was not. In tightly closed, completely filled vials with high ratio of ruminal fluid to sample, AC increased greatly and rapidly, i.e., in 6 h. This time could be further reduced to 2 h by overnight “preincubation” of the ruminal fluid with cotton fiber before starting the test incubation. Certain surfactants used to aid wetting of the fiber had a low but measurable potency in inhibiting cellulose digestion, but other surfactants were non-inhibitory. The AC response was maintained when ruminal fluid was diluted with an equal amount of McDougall's “artificial saliva” solution.

Monensin, a polyether antibiotic, was blended with a forage diet at levels of 0, 11, 22 and 33 ppm and fed to steers to determine its effect on cotton fiber, dietary carbohydrate and nitrogen digestibility, on numbers of ruminal microbes, and on concentration of ruminal volatile fatty acids. No differences (P>.10) in cellulose digestibility from cotton were observed in response to monensin level when cotton fiber samples were incubated in vitro in ruminal fluid from these steers. Neither were differences in loss of dry matter detectable (P>.10) when cotton fabric strips were placed within the rumens of steers for 72 hours. In vivo digestion of dry matter, crude protein, hemicellulose and cellulose of the forage diet was not different (P>.05) among treatments. Total ruminal volatile fatty acid concentration was not affected by feeding monensin, but the molar proportion of acetic acid decreased (P<.01) from 66.7 to 61.3% and that of propionic acid increased (P<.01) from 20.1 to 26.1%. No other volatile fatty acids were affected. Neither the numbers of protozoa, total bacteria nor cellulolytic bacteria in ruminal fluid were affected by feeding up to 33 ppm dietary monensin.

Most of the.commercial cotton fiber produced in the United States is subjected to a period of from one to many weeks of exposure to the weather before it is harvested from the plant. Such weathering has been shown in prior work to be a cause of changes in the wax on the fiber [19], in the fiber's swelling behavior in alkali [22]. and, under humid conditions, in the pH of water extracts of the fiber [21]. Subsequent investigation now has revealed that a number of other fiber properties also may undergo change during preharvest weathering. These properties include moisture regain at constant relative humidity, dye absorption, content of water-soluble reducing substances, browning tendency, rate of wetting in a water-alcohol mixture, length, strength, and susceptibility to enzymatic decomposition. As might have been expected, the X-ray angle, as defined by Berkley and co-workers [4], showed little if any alteration. Several of the fiber properties which change during weathering have been measured on commercial fiber samples and the results found to show a relationship to the grade of the fiber. Further work is in progress to analyze the nature of the above fiber property changes and to detect other changes which may occur. A rapid and practical test for measuring the water-soluble copper-reducing constituents in raw cotton fiber is described.

A quantitative technique has been developed in which a weighed sample of cotton fiber is swollen in sodium hydroxide, centrifuged to remove liquid from between the fibers, and re weighed to determine its percentage increase in weight, the latter quantity being designated here as the fiber's "alkali-centrifuge value." The results obtained have been found to be related to two types of causal factors—namely, (1) the prior action of deteriorative agencies on the fiber, apparently especially on the outer wall of the fiber, and (2) the wall thickness of the fiber (as reflected in arealometer air-flow measurements). The fiber-deteriorative agencies which have been shown to bring about changes in the alkali-centrifuge value of cotton fiber include micro-organisms, certain enzymatically active filtrates from microbial growth media, sodium hypochlorite, hydrochloric acid, heat, and weathering. The microbial and enzymatic effects have been studied in more detail than the others. The new test is simple, rapid, inexpensive, quite highly reproducible, involves only standard laboratory equipment, and is essentially free from safety hazards to the operator. Several aspects of the methodology of the test are reported.