Alterations in ruminal utilization of magnesium and zinc in lambs fed different ratios of concentrate: forage.

Twelve wether lambs were used to study the effects of concentrate level on ruminal utilization of Mg and Zn. Treatments consisted of concentrate: forage ratios (C:F) of 10:90, 40:60, and 70:30. Ruminal pH.hours (pH x hours area below 6.7 in 24-hour period) increased (P less than .01; linear) with increasing C:F. Bacterial intestinal Mg flow increased (P less than .01; linear) with increasing C:F and was strongly correlated with pH.hours (r = .75, P = .008). Ruminal Mg absorption was not affected (P greater than .05) by C:F, but correlated well with bacterial intestinal Mg flow (r = .66; P = .026). As with Mg, intestinal flow of bacterial Zn increased (P less than .01; linear) with increasing C:F and was highly correlated with pH.hours (r = .76, P = .006). Ruminal Zn absorption declined (P less than .05; linear) with increasing C:F and correlated well with bacterial Zn flow (r = -.82, P = .002). Data suggest that ruminal pH and (or) bacterial accumulation of Mg and Zn may compromise ruminal absorption of these minerals.