Dairy cows are often accused of contributing to climate change because rumen fermentation results in some greenhouse gases (largely methane and carbon dioxide) being produced. Whether the accusations are fair or accurately ascribed to these animals is fodder for another discussion. However, efforts are being made to reduce output of these gases, with the responsibility most often placed on the farm.
Bear in mind, energy that is given up to the atmosphere represents a loss in energy that might otherwise be used by the cow. Thus, means to reduce methane output from the rumen can potentially contribute to energy being more available for milk production.
The other major source of methane is from manure, which is undigested feed. Manure in piles or slurries support the growth of methane producing bacteria. Although this can be harvested and used as a source of energy, this energy would likewise be better used if it were available to the cow.
Many research endeavors are underway to develop products to assist in reducing methane output from the rumen. Some, however, accomplish this by reducing overall rumen digestion, which only shifts methane production from the rumen to the manure pile. The best use of the recovered energy would be to support milk production and provide economic value to the farm. Fortunately, the selection of feed ingredients can make important contributions towards reducing methane production. Vegetable proteins in particular can modify methane production in the rumen.
Most of the vegetable proteins available for feeding are coproducts of the edible oil industry and as such vary in their fatty acid content and composition. Oils found in vegetable proteins are known to contain unsaturated fatty acids which in broad strokes are problematic for digestion when fed in large amounts. However, vegetable proteins differ in the number of unsaturated double bond units. Stearic acid, a saturated fatty acid, has no double bonds acid and is inert in the rumen. The most common unsaturated fatty acids found in vegetable proteins are oleic acid, linoleic acid and linolenic acid. Oleic acid has one double bond, linoleic acid has two double bonds and linolenic acid has 3 double bonds. As Table 1 shows, most vegetable proteins are rich in linoleic acid. The clear exceptions are canola meal, which is rich in oleic acid, and linseed meal (also called flax meal) which supplies linolenic acid.
Research conducted by Agriculture and Agri-Food Canada under the guidance of Dr. Karen Beauchemin clearly demonstrated that the selection of vegetable proteins can impact methane production. In an experiment published in the Journal of Dairy Science (Volume 92, pages 2118 to 2127) the effects of these fatty acids on methane production were compared. Diets were formulated to provide 3.7% added fatty acids from rumen inert fat (control), canola seed, linseed, or sunflower seed and were given to cows that were past peak in milk production.
The results show that all the oilseeds helped to reduce methane output by the rumen, when compared to the control diet. Dry matter intake was improved with the canola meal diet, when compared to the control diet. Although milk production was not affected by the diet, there were substantial differences in daily weight gain. Cows gained the most weight with the fatty acids from canola, and the least with the high linoleic acid sunflower meal.
It is important to the dairy industry to reduce methane production. However, this should not be limited to the rumen alone, and the effects of methane reducing compounds on digestibility need to be determined. Importantly, the benefit to the economic return to the farm needs to be included in the analysis. In this case, there were no significant differences in milk production. However, cows given the diet high in linoleic acid (sunflower) were unable to put back the weight that would have been lost in early lactation.
Researchers are developing methods to assist dairy farmers in addressing the greenhouse gas issue head on. Ingredients such as vegetable proteins now need to be considered in formulations not just for their amino acid profile, but also for their fatty acid contributions to the diet.
Essi Evans, Ph.D is President of E+E Technical Advisory Services. She earned her B.S. from the University of Maryland, and Masters and PhD degrees in ruminant nutrition from the University of Guelph. Her firm provides technical and managerial support for nutrition companies along with assistance with research and product development. Brittany Dyck is with the Canola Council of Canada.