PSVIII-7 - Impact of Virginiamycin on Rumen Fermentation and Methane Production in a Lactation Diet

Abstract: To further understand the mode of action of virginiamycin (VM), an in vitro rumen fermentation study was conducted to determine the effects of VM on rumen fermentation and methane production using lactation diets. VM is approved for the control of liver abscesses in the United States and in preventing or treating ruminal acidosis in other countries. Three ruminally cannulated Jersey heifers were adapted to 53:47 forage to concentrate ratio diet for two weeks before use as rumen fluid donors. The treatments were control (CON) and VM (25 ppm). Diet was dried, ground to 1mm and used as substrate. Rumen fluid was collected two hours after feeding. Substrate (0.5 g) was inoculated with 100 mL of a 3:1 McDougall’s buffer:ruminal fluid mixture for 24 h at 39°C and constant agitation. Each treatment was run in triplicate and in three runs. Data were analyzed with a mixed model including treatment as the fixed effect and experimental run as a random effect using SAS software 9.4. Statistical significance was set when P≤0.05. Maximum gas production was less (P < 0.01) in VM compared with CON (100 vs. 130 mL/g incubated DM). VM tended to reduce methane production per unit digested DM (6.71 vs. 9.88 mg/g digested DM; P=0.07) and per unit incubated DM (4.40 vs. 7.16 mg/g incubated DM; P=0.06). VM increased propionate molar % compared to CON (21.4 vs. 16.2%, P< 0.01). VM reduced acetate:propionate compared to CON (2.84 vs. 3.85, P = 0.01). VM reduced DMD (65.5 vs. 72.5%, P=0.02) without reducing total VFA concentration compared with CON. VM tended to increase pH compared with CON (6.73 vs. 6.68, P=0.07). VM reduced methane production, increased propionate proportion, and maintained rumen pH in an in vitro fermentation system using an early lactation diet.