Graduate Thesis Or Dissertation
 

Some techniques for determining fecal output and digestibility of range forage by cattle

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  • A Cr₂0₃, and cellulose fibre mixture was used with cattle, in three grazing and two semi-restricted experiments, to study the mode of its excretion, the possibility of using it in a once-daily dosing and grab-sample regime to estimate fecal output and in a field experiment to test a hypothesis involving the measurement of forage intake. The cattle consumed forages available in the sagebrush-bunchgrass region of Eastern Oregon, in which region the experiments were conducted. Cr₂0₃-Cellulose was fed to groups of three steers grazing immature crested wheatgrass, (Agropyron desertorum) in Experiment 1, or when it was mature along with regrowth in Experiment 2, either once a day at 8 a.m. or twice daily at 8 a.m. and 4 p.m. Twice a day grab sampling was carried out from 3-18 days after commencement of dosing with total collections from days 3-8 and 13-18. Estimated fecal outputs based on fecal grab sample concentrations at 8 a.m. alone, or the mean of 8 a.m. and 4 p.m. values were calculated in both experiments. Cr₂0₃ recoveries in Experiment 1 were low, ranging from 71.1-85.4 percent, with individual animals varying little between collection periods. Estimated fecal dry matter output was high in both groups for both collection periods and both sampling time methods, ranging from 115.7-187.3 percent. Standard errors of the mean (S.E.) were high in the 8 a.m. group in both collection periods, though not in the twice-daily group. Recoveries in Experiment 2 varied from 94.9-107.6 percent with an overall mean of 100.8 percent. The ratio of estimated fecal dry matter to that collected had high S.E.'s in the first period but gave the following results in the second period: 84.3 percent ± 4.5 percent S.E. for 8 a.m. dosing and sampling; 95.0 percent ± 1.5 percent for 8 a.m. and 4 p.m. dosing with 8 a.m. sampling; 97.1 percent ± 3.8 percent for 8 a.m. dosing and 8 a.m. and 4 p.m. sampling and 95.6 percent ± 2.0 percent for 8 a.m. and 4 p.m. dosing and sampling. The four-hourly Cr₂0₃ excretion curve of two groups of two long yearling heifers, two months pregnant, having continued access to flood meadow hay, was established by either once or twice daily dosing. The group dosed, once daily showed a relatively regular diurnal pattern, the twice-daily dosed group less so. The ratio of 8 a.m., and mean of 8 a.m. and 4 p.m. fecal Cr₂0₃ levels to daily mean four-hourly levels was established over a five-day period and showed a very close relationship to percentage estimates obtained in Experiment 2 for the 8 a.m. dosed and sampled group and to a slightly lesser extent to the other three groups. The excretion curve from a single ten gram dose of Cr₂0₃ as Cr₂0₃-Cellulose in two steers showed appreciable Cr₂0₃ in the feces within ten hours, a peak from approximately 18-26 hours in the better steer and levels near the limit of analytical accuracy from three to five days. The hypothesis, that poorer growth observed from forced feeding of common salt late in the grazing season was due to depressed forage intake, was rejected, using Lancaster's fecal nitrogen method for determining digestibility and once-daily Cr₂0₃ dosing and sampling with corrections obtained from Experiment 2 for fecal output to measure forage intake. Grab sample Cr₂0₃ concentration was significantly higher in the morning sample than the afternoon in all experiments. Coefficients of variation were higher in the morning for once daily dosing and higher in the afternoon in twice daily dosing. A series of 12 animal experiments and two simplified laboratory experiments were used to determine whether small nylon or cellulose acetate bags placed in the rumen could be passed through the alimentary tract and used as a possible method of measuring over-all forage digestibility. Bags tied to the fistula bung by nylon line were recovered intact at ten days. Rumen evacuation in cattle showed that nearly all bags placed free in the rumen had disappeared by three days with evidence of regurgitation on three occasions and only two free, intact bags. Sheep experiments by dosing and direct surgical placement in the rumen confirmed that regurgitation occurred. In a final slaughter experiment colored polyethylene and glass beads showed most, if not all, bags had been broken before reaching the reticulo-omasal orifice. All experimental observations on the fate of the bags are consistent with the following explanation. The bags in the rumen are subject to regurgitation; they cannot leave the rumen until this happens, following which the fragments are swallowed and are of a specific gravity and size that ensures their passage through the reticulo-omasal orifice. However, they are then dissolved in the acid environment of the lower stomachs. Although the problems of using the bag technique appear insurmountable, the manner of bag movements is believed to be fully understood.
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Déclaration de droits
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