The rumen allows cattle to make highly nutritious beef out of things that humans can’t even digest. Rumen microbes have digestive enzymes that mammals don’t. This allows rumen microbes to break down complex feeds into very simple molecules, and reassemble those molecules into volatile fatty acids that the animal can absorb and use as an energy source. These microbes can also take some simple nitrogen-based compounds like ammonia and urea, turn them into amino acids, and assemble those amino acids into microbial proteins that the animal can digest and absorb. But the rumen can be wasteful as well. Some rumen microbes assemble carbon (C) and hydrogen (H) molecules together into methane (CH4) instead of volatile fatty acids. The animal can’t absorb or use methane, so methane gets belched out. This can waste significant feed energy — methane is the main ingredient in natural gas, after all. If we can find a way to reduce methane production in the rumen, we may be able to further improve feed efficiency and shrink beef’s environmental footprint at the same time.
A team of scientists led by Karen Beauchemin at Agriculture and Agri-Food Canada’s Lethbridge Research Centre has been studying whether feeding nitrate can reduce methane production without risking nitrate poisoning (Journal of Animal Science 95:3700-3711 and 95:3712-3726). The theory is that the hydrogen (H) molecules in the rumen will attach to the nitrogen (N) molecule from the nitrate instead of carbon (C), thus producing ammonia (NH3) instead of methane (CH4). Then the rumen microbes can convert the NH3 into amino acids and microbial protein. This could reduce methane production while improving feed efficiency.
What they did: This team fed three different diets to 132 crossbred steers averaging 645 pounds in a backgrounding and finishing study. All three diets contained the same amount of crude protein, but the crude protein sources differed slightly. The control diet contained urea but no nitrate. Another diet replaced some of the urea with 1.25 per cent nitrate. The third diet contained 2.5 per cent nitrate. The nitrate was encapsulated for gradual release to give the rumen microbes a better chance of using it over time, rather than letting the nitrate be absorbed directly into the animal’s bloodstream. The urea and nitrate supplements were mixed in with the grain and silage rather than top-dressed. The cattle were backgrounded (65 per cent corn silage, 25 per cent barley grain) for 91 days then finished (10 per cent corn silage, 80 per cent barley grain) for 150 days. A sample of 20 steers were used for methane measurements during both the backgrounding and finishing periods. Animal intake and weights, feed and blood samples, and carcass measurements were also collected.
What they learned: In measuring performance, dry matter intake, growth rate and feed:gain were similar for all three groups during the backgrounding period. In the finishing period, the 2.5 per cent group ate slightly less than the other two groups but gained just as fast, meaning that the 2.5 per cent group converted slightly more efficiently than either the 1.25 per cent or control groups.
Methane production was highest for the control, intermediate for the 1.25 per cent and lowest for the 2.5 per cent nitrate group during the backgrounding period, but these differences were not statistically significant. No differences were seen during the finishing period either.
Health: Blood samples showed no evidence of nitrate poisoning, and no animals exhibited signs of nitrate poisoning during either the backgrounding or finishing periods.
Carcass traits and liver abscess scores were similar among groups. Nitrate levels in meat and organs were virtually undetectable, and far below the levels allowed when nitrate is used to cure meat products.
Feed sorting appeared to differ among the three groups. The urea and nitrate particles were small but similarly sized, so the percentage of large (e.g. silage), medium (e.g. rolled grain) and small (e.g. nitrate and urea) particles were similar in all three total mixed rations. But when weekly samples of uneaten backgrounding ration were collected from the bunk and analyzed, the 2.5 per cent diet contained a lower proportion of large and medium particles, and a greater proportion of small particles than the control and 1.25 per cent diets. In the finishing diets, the 2.5 per cent and 1.25 per cent diets contained a lower proportion of large and medium particles, and a greater proportion of small particles than the control diet. It looked as though the cattle may have been trying to avoid the nitrate, especially in the finishing diet.
What it means: Feeding nitrate didn’t reduce methane production, but it may have improved feed efficiency with no adverse health effects. The apparent undesirable flavour of nitrate tastes may even be useful. An earlier study monitored feeding behaviour in individually fed cattle. Compared to cattle receiving no nitrate, cattle fed nitrate ate just as much, but they ate smaller meals, more often, and had more stable rumen pH. If further research demonstrates similar effects in group-fed cattle, perhaps nitrate can help manipulate feeding behavior, modulate rumen pH, reduce acidosis and help maintain liver health in feedlot cattle.
The Beef Research Cluster is funded by the Canadian Beef Cattle Check-Off and Agriculture and Agri-Food Canada with additional contributions from provincial beef industry groups and governments to advance research and technology transfer supporting the Canadian beef industry’s vision to be recognized as a preferred supplier of healthy, high-quality beef, cattle and genetics.