The effect of infusion of putrescine and gamma amino butyric acid on the intake of steers offered grass silage containing three levels of lactic acid

An experiment was carried out to assess the role of putrescine (P) and gamma amino butyric acid (GABA) on the intake of grass silage containing three levels of lactic acid. The experimental design involved a nine period, 3 × 3 factorial changeover design experiment, with each period of 14 days duration. Putrescine and GABA were applied at a rate of 6 g kg−1 dry matter (DM), dissolved in 4 I water and intraruminally infused using a peristaltic pump with the amount infused varied throughout the day by means of an electronic time-switch attached to the infusion pump. (This was an attempt to match the amount infused with the amount the animal would have consumed if the treatment had been added to the diet.) The basal diet consisted of a well fermented grass silage with 116 g lactic acid kg−1 DM. Lactic acid was added to the basal diet at levels of 0, 50 and 100 g kg−1 DM to give final lactic acid concentrations of 116 (L1), 160 (L2) and 188 (L3) g kg−1 DM, respectively. No significant interactions between infusion treatment and level of lactic acid were observed on intake, eating behaviour, rumen fermentation parameters or dry matter, nitrogen, modified acid detergent fibre (MADF) or acid detergent fibre (ADF) degradability characteristics of silage. Main treatment effects only are presented. Putrescine and GABA did not significantly (P > 0.05) affect dry matter intake or feeding behaviour. L2 significantly increased total time spent eating per day (P < 0.05), reduced daily eating rate (P < 0.001) and reduced mean eating rate during the secondary meals (P < 0.001). Infusion of P increased rumen fluid pH (P < 0.05). GABA infusion reduced the molar proportion of propionic acid (P < 0.05) and increased total i-butyric acid concentration (P < 0.05). L3 increased total concentration of n-butyric acid (P < 0.05); L2 and L3 increased the molar proportion of n-butyric acid (P < 0.05). Lactic acid treatment had no significant effect (P > 0.05) on DM, N or MADF degradability characteristics. However, L3 reduced NDF degradability (P < 0.05). Infusion treatment had no significant effect (P > 0.05) on DM, MADF or NDF degradability characteristics. However, P reduced nitrogen degradability (P < 0.01).