Grass hay as a supplement for grazing cattle. II. Ruminal digesta kinetics.

Abstract

This study evaluated the effects of supplementing a diet of range hay (5.7% crude protein, 68% NDF) with grass hay from subirrigated meadows (16.5% crude protein, 53.5% NDF), or with a 70% soybean meal:30% wheat grain supplement (40% crude protein) on intake and ruminal digesta kinetics. Twelve ruminally fistulated steers were assigned to 3 treatments (4 steers/treatment) at 2 levels of intake. Treatments were: control, range hay; range hay supplemented with meadow hay (meadow hay was 20% of intake); and range hay supplemented with soybean meal:wheat supplement (supplement was 8% of intake). Intake levels were: ad libitum and equal intake (1.5% of body weight). Range hay was Yb-labeled, and meadow hay and soybean meal:wheat supplements were Er-labeled to measure passage. Intake and digestibility of range hay was not affected by supplementation (P > 0.05). During ad libitum intake, total intake (range hay + supplement) was greater (P > 0.05) for supplement treatments than for the control. No supplement treatment X level of intake interactions were detected (P > 0.05). Total digestibility (range hay + supplement) was greater (P < 0.01) for the soybean meal:wheat treatment than for the control or meadow hay treatments. Total digestibility was similar (P > 0.05) for control and meadow hay treatments. Ruminal passage rate (% hour-1), total tract mean retention time, and intestinal transit time of range hay did not differ among treatments (P > 0.05), but ruminal passage rate, total tract mean retention time, and intestinal transit time were greater (P < 0.01) with ad libitum than equal intake. We conclude that a meadow hay supplement produced similar effects on ruminal kinetics and intake of range hay as a soybean meal:wheat supplement.