Effect of molasses, sodium bentonite and zeolite on urea toxicity

Abstract

Molasses, sodium bentonite (montmorillonite clay) and zeolite (crushed clinoptilolite rock) were examined as supplement ingredients to improve the safety margin of urea supplementation in a series of seven experiments. These experiments were designed to provide an understanding of the relationship between urea intake and the influence of the above ingredients on rumen pH and total ammonia concentrations. Rumen fistulated Merino ewes of 35-40 kg liveweight were administered various amounts of urea with and without supplement mixes. Rumen parameters were measured at 0, 0.5, 1-0, 1.5, 2.5, 5.0 and 24 h after treatment administration. Acetic acid and sucrose were also tested together with molasses for comparative effects on rumen parameters. In the last experiment, blood pH and total plasma ammonia were also determined. Free ammonia values of rumen liquor were calculated for experiments 2 to 7. In four experiments, molasses at 50, 100 and/or 150 g mixed with urea significantly reduced the normal rapid rise in ruminal pH, total and free ammonia values compared with urea (10 g) only treatments. In two experiments, associated presence or absence of clinical toxicity at various quantities of urea (8 to 25 g) with and without active ingredients confirmed the postive effect of molasses in preventing toxicity at <0.44 g urea/ kg liveweight. The addition of molasses reduced the increase in ruminal pH by up to 0-5 pH units and absolute values were consistently below pH 7-0. Sucrose (100 g) and acetic acid (800 mL of 1 M ) had the same and greater effect, respectively, compared with molasses (150 g) when added with urea (10 g) on ruminal pH and total and free ammonia changes over five hours post treatment. The partly hydrated urea / bentonite mix (approx 1 : 1 bentonite : water ratio) was associated with a delay in the increases in ruminal pH and free ammonia concentrations. Bentonite mixes, in either fully hydrated or fully dehydrated states, and zeolite mixes resulted in no significant effects. With reference to previous reports, the results support the positive role of a stable acid pH in the rumen for ensuring safe urea supplementation.