Rumen fermentation and digesta passage in ruminants fed cimaterol

Abstract

In Experiment 1, rumen fluid samples were collected from 12 Finnish Landrace crossbred wether lambs following slaughter after a 64 day experimental period during which they were offered a pelleted concentrate ration ad libitum. Cimaterol was included in the concentrate ration at 0 or 10 mg kg −1. Neither ammonia and volatile fatty acid (VFA) concentrations, nor acetate, propionate or butyrate proportions of VFA were affected by dietary cimaterol inclusion. In Experiment 2, eight ruminally fistulated Friesian steers were fed either 0 or 0.09 mg cimaterol kg −1 body weight (BW) in a ration consisting of 340 g concentrate and 660 g hay kg −1 dry matter (DM). The allowance of 15.5 g DM kg −1 BW was fed in two equal portions daily for 35 days. Rumen fluid samples were collected immediately before the first feed and 2, 4, 8, 12, 16 and 24 h thereafter on two occasions. Rumen liquid and solid turnover were measured by ruminal pulse dosing with cobalt-EDTA and ytterbium-labelled hay, respectively. Dietary inclusion of cimaterol did not affect rumen fluid pH and concentrations of ammonia or VFA in rumen fluid, but increased the acetate and propionate proportions of VFA and decreased the butyrate proportion of VFA, particularly after the second daily feed. These effects resulted in significant alterations in the acetate to propionate and non-glucogenic ( acetate + 2- butyrate propionate ) ratio. Dietary inclusion of cimaterol did not affect rumen liquid or solid digesta turnover. It was concluded that cimaterol had a small but beneficial effect for growth on the concentration of measured end-products of ruminal metabolism, but had no effect on digesta passage from the rumen.