Effects of Dietary Glycerin on Rumen Metabolism of Beef Cattle Fed 50% Dried Distillers Grains with Solubles

Abstract Text: Glycerin improves ADG, efficiency, and marbling scores in beef cattle when fed as a supplemental energy source; however, less is known about its ruminal effects. We hypothesized increasing glycerin in the diet would increase ruminal pH, ruminal propionate concentration (Pr), and in situ fiber disappearance; but decrease ruminal hydrogen sulfide gas concentrations (H₂S) in cattle fed dried distillers grains with solubles (DDGS)-based diets. Objectives of this study were to determine effects of 0, 8, and 16% dietary glycerin inclusion on ruminal metabolism of beef steers fed 50% DDGS (DM basis). Six cannulated steers (initial BW=656 ± 71 kg) were used in a replicated 3×3 Latin square design. Steers were allotted to 1 of 3 dietary treatments: (1) 0% glycerin, (2) 8% glycerin, or (3) 16% glycerin (DM basis). The remainder of the diets consisted of 50% DDGS, 20% silage, 10% supplement, and corn (DM basis). Glycerin replaced corn, on a DM basis, in the diet. Steers were fed once daily for ad-libitum intake and given 14d dietary adaptation at the start of each new feeding period. Then, rumen fluid samples were collected for pH, H₂S, and VFA on d 15 of each period. On d 16, a 24h in situ incubation was conducted. Steers fed increasing glycerin inclusions in the diet tended (linear; P = 0.06) to decrease DMI. There was no effect (P ≥ 0.38) of glycerin inclusion on 24h in situ DM or NDF disappearance. Although there was a time by glycerin inclusion interaction (P < 0.01) for ruminal pH, mean ruminal pH did not differ (P = 0.88) as steers were fed increasing glycerin (6.06, 6.08, and 6.11, respectively). There was a time by glycerin inclusion interaction (P = 0.05) for acetate concentration (Ac). At 0h post-feeding there was no effect on Ac; however, at 3 and 6h post-feeding, Ac was reduced with increasing glycerin inclusion. Mean Pr was increased (linear; P = 0.01) with increasing dietary glycerin inclusion. Due to reduced Ac and increased Pr, mean Ac to Pr ratio decreased (linear, P < 0.01) with increasing glycerin. As glycerin inclusion increased, mean H₂S decreased (linear; P = 0.05). Mean ruminal H₂S at 0, 8, and 16% glycerin inclusion were 658.06, 515.83, and 477.22 mg H₂S per L, respectively. Contrary to our hypothesis, fiber digestion was not increased in steers fed increasing glycerin; however, ruminal Pr was increased.

Keywords: beef cattle, distillers grains, glycerin