The effect of intraruminal infusions of amines and gamma amino butyric acid on rumen fermentation parameters and food intake of steers offered grass silage

Abstract

An experiment was carried out to assess the role of amines and gamma amino butyric acid (GABA) in food intake control with steers offered grass silage based diets. The effect of the amines, putrescine (P) and tyramine (T), and GABA (G) on voluntary food intake were investigated at three levels of addition: 2 g kg −1 DM (1); 4 g kg −1 DM (2) and 6 g kg −1 DM (3). An additional ‘control’ treatment involved infusion of water. A ten period changeover design experiment was used, with four steers, mean liveweight 597 ± 38 kg, fitted with rumen cannulae. The basal diet consisted of an extensively fermented grass silage offered ad libitum. Each period was of one week duration. Following a 4 day preliminary period, amines, GABA or water were infused into the rumen for 3 days for 8 h per day. Daily dry matter intake was recorded in addition to intakes at various time intervals throughout the day. Rumen samples were also taken throughout a 24 h period on Day 3 of each experimental period. No significant ( P > 0.05) treatment effects on DM intake were observed with dry matter intakes (g kg −1 LW) as follows: 13.1 (C); 13.7 (P1); 13.2 (P2); 12.7 (P3); 13.7 (G1); 13.8 (G2); 13.9 (G3); 14.2 (T1); 14.1 (T2) and 13.2 (T3) SED (0.68). Tyramine infusion at 6 g kg −1 DM significantly ( P < 0.05) increased rumen fluid pH, GABA infusion at 2 g kg −1 DM significantly ( P < 0.05) reduced the proportion of propionate and tyramine infusion at 2 and 6 g kg −1 DM significantly ( P < 0.05) increased isovalerate proportion in rumen fluid. These results suggest that infusion of putrescine, tyramine and GABA into the rumen at levels up to 6 g kg −1 DM intake, do not significantly affect voluntary food intake with steers offered an extensively fermented grass silage.