Influences of Feed Additives on in vitro Volatile Fatty Acid Production

This study investigated effects of the feed additives nitrate and fumarate alone or in combination on in vitro Volatile Fatty Acid (VFA) production. Rumen fluid was collected from Holstein-Friesian cattle averaging 650 kg in BW (body weight) offered 11.4 kg d^-1 per animal of concentrate diet containing equal amounts of soybean meal, whole cottonseed and ground corn once a day with free access to grass hay. The feed additives used were nitrate, fumarate and a nitrate-fumarate combination. Concentrations of VFAs were measured using Gas Chromatography. The results of the study revealed that nitrate decreased (p<0.05) individual VFA production compared to the control and all other feed additives. The addition of fumarate had no effect on VFA production. The addition of the nitrate-fumarate combination decreased (p<0.05) butyrate and iso-butyrate production compared to the control and had no effect on all other individual VFAs. The addition of nitrate also increased (p<0.05) the acetate to propionate ratio compared to the control, fumarate or nitrate-fumarate combination. The addition of fumarate and nitrate-fumarate had no effect on the acetate to propionate ratio compared to the control. The current study suggests that nitrate alone may have an adverse effect on microbial fermentation if VFA production is significantly decreased. Therefore, the addition of the nitrate-fumarate combination may reduce the potential negative effects of nitrate on VFA production.