The dietary starch content recommendation for lactating dairy cows is between 23 percent and 26 percent. However, diets for some of the most productive herds in the U.S. contain between 15 percent and 30 percent starch.
The possibility of $8 corn has increased interest in feeding lower-starch diets to cattle. In a previous article, I stressed exploring alternatives but purposely ignored specific examples to provide an overview of management considerations not limited to feed alone.
Corn is king and often the preferred energy source for many good reasons until supply and cost become limiting. Corn grain can be reduced and perhaps replaced with a variety of byproduct feeds high in digestible fiber in lactating dairy cow diets, resulting in a low-starch diet without adversely affecting lactational performance and ruminal fermentation.
Many nonforage fiber sources, such as soybean hulls, beet pulp, corn gluten feed and dried distillers grains with solubles, are characterized by a low starch content, high fiber digestibility and variable content of soluble fiber and sugar. They are ideal for replacing corn starch with nonforage fiber sources.
And don’t overlook the replacement of corn starch with sugar sources. Molasses or other liquid products also are available locally. Replacing corn with starch from potatoes or sugar from beet sources in high-forage (60-to-40 forage-to-concentrate ratio) diets containing alfalfa silage and corn silage is a viable strategy for reducing dietary starch content while maintaining milk yield.
While my dairy research has not included feeding these products, I am a proponent of beet pulp, probably the “queen” of all byproducts. It fits so well in dairy cow diets, especially during the transition period.
Furthermore, NDSU beef researchers have conducted experiments that support the benefits of feeding sugar and balancing ruminal carbohydrates. This research can be applied to dairy diets. North Dakota is awash in byproducts. The use of nonforage fiber sources is a practical way to reduce the dietary starch content while maintaining lactational performance.
Another feasible strategy to reduce the dietary starch content is to replace corn with high-quality forage. Researchers at the U.S. Dairy Forage Research Center, Madison, Wis., varied the forage-to-concentrate ratio from 35-to-65 to 80-to-20 and the starch content from 38.3 to 12.3 percent of diets for lactating cows by substituting alfalfa silage for high-moisture ear corn and soybean meal. They noted that reducing the dietary starch content to less than 20.7 percent (65-to-35 forage-to-concentrate ratio) should be avoided when substituting alfalfa silage for high corn starch.
Researchers at the Miner Institute, Chazy, N.Y., working with corn grain, corn silage and byproducts observed no effect on feed intake, milk component production, ruminal metabolism or microbial protein yield when dietary starch was varied between 18 and 25 percent.
What is important to note is that, as dietary starch decreased, the digestibility of that starch increased simultaneously. When predicting the potential impact of starch content of the diet on animal response, nutritionists and herd managers need to consider not only the amount but the digestibility of the starch.
Ultimately, the cow needs a certain amount of rumen-fermentable starch, or fermentable carbohydrate, which will be a function of the amount and the digestibility of the starch and other carbohydrate fractions.
Reducing starch carries some cautions, however. You need to watch the cows when feeding low-starch diets. Most of the research conducted with low-starch diets has been short term (less than eight weeks) and focused on midlactation cows. The long-term effect of feeding low-starch diets to cows in all stages of lactation is unknown. Therefore, when implementing low-starch diets on an entire herd basis, the nutritionist and dairy producer should watch for signs that may indicate the dietary starch content is too low.
Signs include decreased milk production, milk protein content and yield, and body condition and weight; increased milk urea nitrogen; and stiffer manure. In addition to watching the cows, feed ingredients should be monitored for changes in neutral detergent fiber (NDF) and starch digestibility. Providing the proper amounts of ruminal-fermentable carbohydrates is critical to optimizing ruminal fermentation and generating volatile fatty acids and microbial protein for energy and amino acid for the cow to use.
Recently, suggested strategies for formulating lactating cow diets when corn prices are high include using more high-quality forage and byproduct feeds to provide highly digestible NDF and nonfiber carbohydrates. Dietary starch content between 18 percent and 21 percent appears to be acceptable when high-quality forages are fed and the dietary starch is highly fermentable in the rumen.
The price for corn grain as a livestock feed has increased substantially during the past two years. Consequently, lower-starch feeding strategies that minimize the amount of corn may be more profitable than higher-starch diets, particularly if lactation performance and ruminal fermentation are not compromised.
So, work with your nutritionist because no two situations are exactly alike. However, one recommendation remains unchanged: Don’t give up milk. Milk price is the driving force for margins, more so than feed cost. While we recoil from the current high feed prices, this is no time to skimp on rations. Considering recent milk price hikes, any loss of milk production would result in lower net income.