by Rick Grant
The author is president of William H. Miner Agricultural Research Institute, Chazy, N.Y.
We know that dairy cows and rumen microbes do not have an actual starch requirement. Rather, rumen microbes require adequate fermentable carbohydrates (starch, sugars, soluble fiber and digestible fiber) to provide energy for microbial protein synthesis.
Over 5 pounds of microbial protein are synthesized every day to help the cow satisfy her protein needs. Additionally, the volatile fatty acids produced by the microbes during fermentation provide up to 80 percent of the cow's energy needs. The rations we feed to lactating cows must provide sufficient rumen-fermentable carbohydrates from grain and forage so that microbial fermentation and milk production are not restricted.
Lower starch diets work
Research conducted during the past five years at Miner Institute has shown that performance is similar for high-producing, midlactation cows fed rations with starch contents ranging from 18 to 25 percent of dry matter. As corn meal is removed from the diet, a key to success appears to be maintaining sufficient rumen-fermentable carbohydrates. This is achieved with either by-product feeds or high-quality forages such as brown midrib corn silage.
It will be challenging to maintain milk production with higher forage diets unless highly digestible forages are used, and even then it may be difficult to drop ration starch below 20 percent.
Lower starch diets can be successfully fed to dry cows, fresh cows and early-lactation cows without compromising any aspect of performance. In fact, fresh cows fed a diet with 18 or 21 percent starch had superior dry matter intake and milk yield during the first 90 days in milk than cows fed a 25 percent starch diet.
These diets were formulated by partially replacing corn meal with wheat mids and beet pulp. Whether starch content is reduced by using fibrous by-products or by feeding a higher forage-to-concentrate ratio will depend on the relative price of feed ingredients.
Era of higher corn price
Until recently, corn grain was relatively inexpensive, so there was little incentive in the U.S. to formulate diets lower in starch and higher in alternative fermentable carbohydrates. However, since 2007 the price of corn grain in the U.S. has been higher than any time during the previous 30 years (with the exception of 1996). Most forecasts are for the corn price to remain between $4 and $7 per bushel in the future, and this year's drought and shrunken corn crop will likely push prices higher still.
Although corn and other feed prices may continue to fluctuate, rations are now being formulated in a new era of substantially higher prices. And, higher corn prices appear to be driving a trend toward lower starch content of dairy rations.
Trends in starch content
In the past few months I have informally polled university and industry nutritionists across the country as to what they were observing for trends in dietary starch content.
Across the Upper Midwest, it appears that, over the past five years, ration starch concentrations have fallen from 25 to 30 percent down to a more modest 23 to 25 percent. In the western Corn Belt region where ethanol plants produce large amounts of distillers grains, the dietary starch content has trended from 26 to 28 percent down to less than 25 percent and as low as 20 percent over the past several years.
About five years ago, Larry Chase from Cornell University published results of a field survey showing that high-producing dairy herds in the Northeast and Upper Midwest fed rations that ranged between 21 and 30 percent starch. Clearly, high milk production can be obtained with either lower or higher dietary starch as long as the ration is properly formulated.
Another trend is feeding lower crude protein (CP) diets in an effort to enhance nitrogen efficiency for milk production and limit excretion of nitrogen into the environment. Cornell University researchers have monitored 14 high-producing herds from Wisconsin, Pennsylvania, Michigan and New York that fed low-protein diets (14.3 to 16.5 percent CP). The ration starch content averaged 28.2 percent with a range of 24 to 31.6 percent. With low-CP diets, the trend has been to feed higher starch levels presumably in an effort to avoid any reduction in rumen microbial protein production. Whether or not lower-starch, lower-CP diets can be fed successfully to high-producing cows remains an important unanswered question.
This article appears on page 611 of the September 25, 2012 issue of Hoard's Dairyman.