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

by Martinez, Andres

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 were tested

simultaneously, Mg offered the already established protection against

Ni and Co individually as well as against combinations of the two elements.

However, as the concentrations of Ni and Co increased, the

depression in cellulose digestion also increased, but the protection

offered by Mg decreased.

Copper was found to be highly toxic to rumen microorganisms

(additions of 0.5 [mu]g/ml practically stopped all microbial activity).

Neither Mo nor S or both were effective in alleviating the depression

caused by excessive Cu. In lieu, the simultaneous presence of the

three elements, in concentrations in which individually were non-deleterious

to cellulose digestion, proved toxic to cellulose digestion.

Nonetheless, additions of Mo significantly (P<.05) increased digestion

in the absence of added Cu and S.

A S requirement by rumen microorganisms for optimum cellulose

digestion was established in three separate experiments. A

level of 8.4 [mu]g/ml S--present in the inoculum--did not support adequate

cellulose digestion, whereas, additions of l0 [mu]g/ml S (18.4

[mu]g/ml total S) to the inoculum resulted in maximum digestion.