Abstracts Earth and Environmental Sciences

Effect of some major and trace element interactions upon in vitro rumen cellulose digestion

by Andres Martinez

A series of factorial experiments (4 x 4 and 4 x 4 x 4) was designed to investigate the effects of selected combinations of some major and trace elements upon in vitro rumen cellulose digestion. Inocula, varying in ratios of clarified rumen fluid (strained through No. 50 cheesecloth and centrifuged at 365 x g for 2 minutes) to basal mineral medium to phosphate buffer, were incubated at 39 degrees C with purified cellulose and the corresponding treatments of test elements. After a 24-hr incubation period, cellulose digestion was calculated. In addition, the mineral composition of rumen fluid and rumen bacteria was studied in relation to the mineral composition of the diet of a fistulated steer. Mineral analysis for 6 major and 15 trace elements clearly indicated that, when compared to the diet, concentrations of these elements in the clarified rumen fluid were several times lower, whereas concentrations in rumen bacteria were several times higher. In general, rumen bacteria appeared to concentrate trace elements to a greater extent than major elements with approximately the following overall distribution: elements concentrated in excess of 20 times included Co; 10 to 20 times- -Se; 5 to 10 times- -Na, P, Al, Fe, Mo; 1 to 5 times- -Ca, K, Mg, S, B, Ba, Cd, Cu, F, Mn, Ni, Sr, and Zn. Chromium was the only element found to be in lesser concentrations in rumen bacteria than in the diet. Significant interactions (P< .05) affecting in vitro rumen cellulose digestion were found amongst the following combinations of elements: Mn-Zn, Ca-Zn, Mg-Ca, Mn-Fe, S-Mg-Ni, P-Mg-Ni, Mg-Co, P-Mg-Co, Mg-Co-Ni, and Cu-Mo-S. Additions of non-toxic levels of Mn partially but significantly reversed the inhibition in cellulose digestion caused by additions of excessive Zn. This protective effect remained significant when ratios of clarified rumen fluid to basal mineral medium to phosphate buffer were altered. Similarly, additions of Ca to the incubation medium significantly (P<.05) protected against the toxicity of excessive Zn. The significant (P <.05) depression caused by excessive Ca, on the other hand, was partially but significantly reversed by additions of Mg. Added Fe (only at levels of 10 [mu]g/m1) had some protection against the depression in cellulose digestion caused by excessive Mn. Additions of 0.1 percent NaCl were effective in counteracting the depression in cellulose digestion caused by excesses of KCl, however, additions of larger quantities of NaCl in the presence of 1.0 percent KCl resulted in total suppression of cellulose digestion. Significant interactions (P<.05) were found between S, Mg and Ni. Additions of non-toxic levels of Mg partially reversed the severe depression in digestion caused by excessive Ni with additions of S or P significantly enhancing this protection. Non-toxic levels of Mg were also successful in alleviating the depressing effects of excessive Co. Additions of S or P, however, were ineffective in augmenting the protection offered by Mg. When Mg, Co and Ni…