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University of Illinois at Urbana-Champaign,,4 Urbana 61801
Abstract
The in vitro solubility of biuret was studied and compared with in vivo solubility in the rumen of sheep. Solubility of biuret in ultra-filtered (sterile) rumen fluid, McDougall's buffer and distilled water was 2.21, 2.25 and 2.24 g per 100 ml, respectively. Biuret hydrolyzing enzyme was found to be associated with rumen microorganisms. To study in vivo solubility, 17 g amounts of feed-grade (prilled) biuret was placed in nylon bags which were suspended in the rumen. In a 24-hr. period, 15.3 g (90%) of biuret had disappeared from the nylon bags. The results of in vitro and in vivo studies of the solubility of biuret suggest that feed-grade (prilled) biuret is relatively insoluble as compared to urea.
Biuretolytic activity of sheep rumen fluid was studied in vitro as well as in vivo. To measure in vitro biuret disappearance, whole rumen fluid from biuret-adapted sheep was incubated with 98% pure biuret (3 mg/ml rumen fluid). In 24 hr. of incubation 40% of biuret had disappeared from the incubated rumen fluid. The rate of biuret disappearance in vitro was very slow, some 5 mg biuret per 100 ml of rumen fluid per hour. For the assessment of in vivo disappearance of biuret in the rumen of biuret-adapted sheep, a single dose of 8.5 g of biuret in solution, along with PEG as marker, was intraruminally infused through a rumen cannula after feeding. Samples were taken from the rumen at various time intervals for direct biuret analysis. After 6 hr. only 12% of the biuret remained in the rumen. Degradation of biuret in the rumen was calculated to be 65% with 35% of the dose passing undegraded from the rumen. Rate of biuret disappearance was about 20 mg/100 ml rumen fluid per hour. The results indicate that the rate of biuret degradation in the rumen is the major factor responsible for slow release of ammonia from biuret.
Biuret hydrolysis'by ruminal protozoa was investigated by three methods. First, rumen contents from biuret-adapted sheep were centrifuged at 25 g for 5 rain. to remove protozoa. Centrifugation did not markedly reduce the biuretolytic activity. Secondly, washed suspensions of protozoa were isolated from the biuretadapted sheep and incubated with biuret. Although protozoal activity was maintained, no degradation of biuret was evident in a 6-hr. incubation period. Finally, one biuret-adapted sheep was defaunated with dioctyl sodium sulfosuccinate and the rumen fluid from this sheep was incubated with biuret. Rumen fluid from the defaunated sheep degraded biuret at rates similar to rumen fluid from the control faunated animal. These results suggest that ruminal protozoa play no direct role in the degradation of biuret.
1 Supported in part by: Hatch Grant 20-346, trust funds from Moorman Mfg. Co., Quincy, Ill., and Dow Chemical Co., Midland, Mich.
2 Present address: Department of Urology, Medical Hospital, University of Washington, Seattle 98105.
3 The authors express their sincere appreciation to Dr. C. L. Davis, Department of Dairy Science, University of Illinois, Urbana, for his valuable advice during this study.
4 Department of Animal Science.
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