Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Woldeghebriel, Abraham


This study investigated the effects of feed particle size and nitrate or fumarate alone or in combination on in vitro fermentation, abundances of methanogens, and methane production. Rumen fluid was collected from a Holstein-Friesian dry cow and a steer (experiment 1) and a dry cow and two steers (experiment 2) averaging 625.4 kg in body weight (BW). The cattle were offered 11.4 kg/d per animal of concentrate diet containing equal amounts of soybean meal, whole cottonseed, and ground corn once a day with grass hay at ad libitum (experiment 1) and 15.9 kg/d per animal of total mixed ration (TMR) of silage, hay, corn, corn gluten, soybean meal, and minerals (experiment 2). Feed grab samples were collected, oven-dried, coarsely pulverized in a regular kitchen blender for one minute, and separated into three particle sizes (PS: 0.85, 1.4, and 2.36 mm). The feed additives used were nitrate, fumarate, and a nitrate-fumarate mixture. The fermentation parameters measured after 48h incubation periods were methane (CH4), pH, VFA, nitrate (NO3), and ammonia (NH3). Real-time PCR was used to quantify the relative abundances of total and specific methanogens.