by Tamara Scully
Climate change has become a focus of the dairy industry, both because climate change will impact dairy herd performance and because dairy herds impact greenhouse gas (GHG) emissions. Not only do dairy farmers have to worry about protecting their cows from the impacts of climate change; they also have to worry about the carbon footprint of the herd.
The carbon footprint of the dairy herd is a tricky thing. According to EPA data, about eight percent of the United States’s carbon footprint originates with agriculture, with animal agriculture causing about three percent of the agricultural footprint. Of that three percent, only 0.54 percent originates from dairy. The other 1.2 percent is a by-product of all other animal agriculture.
With such a low percentage not only of the United States’s carbon footprint, but of the carbon footprint attributed directly to agriculture, coming from the dairy industry, it may seem odd that the industry has launched a campaign to reduce the emissions for fluid milk.
The industry has pledged to decrease GHG emissions associated with the production of one gallon of fluid milk by 25 percent by 2020. Most of the carbon footprint in a gallon of milk is directly related to animal agriculture.
“Seventy-two percent of the total GHG per gallon is either in milk production or feed production,” Dr. Larry Chase, Department of Animal Sciences, Cornell University, said.
Studies estimate that wild ruminants — primarily bison — contributed about 86 percent of the current livestock related GHG levels in pre-cow days here in the United States, Chase said. Wild ruminants were foragers — no one was growing grain and mixing feed for them. They were eating native prairie grasses and legumes. So adding domestic cows to the mix hasn’t caused a very drastic increase.
With dairy cows being closely managed for milk production, changes in herd management techniques potentially could impact GHG emissions. Various studies have tried to evaluate the impact of changes in dairy herd management, generating practical and wildly dangerous ways to decrease methane production in dairy herds.
One non-recommended suggestion is to decrease the pH of the rumen below 5.5, which would result in a rapid 15 percent decrease in GHG emissions.
“But you will kill cows rapidly,” Chase warns. “It really doesn’t fit practical management and cow health.”
There are, however, more common sense approaches which dairy farmers can take to reduce their herd’s level of GHG emissions. Increasing fat — up to a certain level, before it becomes problematic — can also decrease GHG emissions by five percent per fat unit increase in the ration.
Increasing forage quality, and therefore increasing the total Neutral Detergent Fiber Digestibility, can increase GHG by about five percent. Better selection of forage type will have similar effects. The best way to approach forage quality is to select the forages that make sense for your farm’s agronomic and environmental considerations, Chase said. Once that is determined, producing the highest quality of those forages is the second piece of the equation.
“I think that’s how you improve,” Chase said. Improving forage quality “is a good, normal management practice anyhow.”
Another study has shown that increasing herd productivity is even more effective than any increase in feed quality alone in reducing GHG emissions. In a study of a 2,200 cow dairy farm, with 1,096 milking cows, non-productive cows contributed roughly 30 percent of the GHG emissions. Decreasing GHG from dry cows and heifers through precision feeding, decreasing the age of first calving and decreasing the amount of replacement heifers are two strategies.
If the culling rate is decreased by five percent, meaning that there are healthier cows requiring less replacement animals, methane emissions can be reduced by about three percent. If the pregnancy rate on dairy farms is increased from the current 20 percent to the 25 percent seen in 1995, methane emissions will be reduced over 10 percent.
Studies on in-vitro additives show short-term, large decreases in methane emissions, but haven’t translated into in-vivo success, Chase said. But a new study of 3-nitrooxypropanol added to the feed of lactating cows did show a 30 percent decrease in methane emissions, and was conducted over a 12 week period.
“There’s promise here,” he said of the study. “Maybe some of these compounds have some potential long-term effects.”
For milking cows, increasing the milk productivity per cow will decrease the GHG emissions per cow. While rBST is one way to increase productivity, it is no longer accepted in many markets. Milking three times per day, increasing feed efficiency and mixing and feeding rations more accurately will all contribute to increased milk per cow, and decreased GHG emissions.
“The more the cow eats, the more methane they produce,” Chase explained, but because milk production increases, the per gallon methane emissions is reduced.
In the long term, Chase said, genomics and genetics will play a role. Selection of sires will include feed efficiency rankings. Methods of altering the rumen microbial population to reduce enteric methane and adding compounds to increase rumen fermentation will also likely be practiced.
Short term strategies for reducing methane emissions from dairy cows include: better feed efficiency through the use of fiber and starch digestibility; feed additives; increased forage quality; better selection of forage type; and a decrease in non-productive cows. Precision feeding and feed consistency — including mixing, delivery and feed bunk management — will help farmers get the most from high-quality forages.
Herd grouping to mix rations for each group’s specific needs leads to more efficiency in converting feed into milk. However, the maximum number of groups that can be managed effectively is three or four, Chase said. Additionally, while increasing feed efficiency will decrease methane, and should be profitable, the volatility of milk and feed pricing may make this less cost effective in some cases. The income/feed cost ratio is an important one.
Better herd management practices today, to increase cow comfort and health, reproductive performance and milk production, are practical and can have immediate impacts on GHG emissions from dairy cows. These adaptations make sense from many different perspectives.
“We need to keep that dairyman profitable at the same time that we impose herd management and lower methane emissions,” Chase said.
Dr. Chase presented this workshop at the July Dairy Environmental System and Climate Adaptation Conference, held at Cornell University.