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Dietary starch in the spotlight at summer research meeting

Carl A. Old Published on 11 September 2014

The American Society of Animal Science and the American Dairy Science Association held their joint annual meeting from July 19 through July 24 in Kansas City, Missouri.

Numerous scientific papers on the topic of nutrition were presented and, while many were of interest to our readers, we chose to report on three. In two of these papers, researchers examined the role of dietary starch and its impact on milk production and animal health, and the other dealt with methane production.

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Study reducing dietary starch
Shane Fredin (currently a post-doctoral researcher at the Miner Institute), Luis Ferrareto and R.D. Shaver, both of the University of Wisconsin – Madison, reported on the effect of reducing dietary starch on intake, lactation performance and ruminal parameters of dairy cows.

Dr. Fredin and his co-workers examined more than 50 studies in which starch, primarily found in cereal grains such as corn, barley and milo, was replaced with non-forage fiber sources, forages or sugars.

High-starch rations contained 28.9 percent starch, and the low-starch rations contained 21.9 percent starch. These investigators found that as starch concentrations were reduced, cows ate less feed and produced not only less milk but also less fat-corrected and energy-corrected milk.

As starch concentration was reduced, milk contained less total butterfat, protein and lactose; however, butterfat concentration (percent butterfat) was not reduced. On the other hand, both lactose and protein concentrations were reduced.

Scientists often choose a probability of 95 percent that defines statistical significance. If they say that this, that or the other thing is statistically significant, then the odds are usually 20-to-1 against the observation being simply by chance.

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In this study, cows ate more feed per unit of milk produced when fed less starch, but the odds of that being by chance were only 16.7-to-1. You’ll never get odds like that in your favor in Reno. Rumen fermentation was affected by feeding less starch, total concentration of volatile fatty acids was reduced and the ever important ratio of acetic acid to propionic acid was greater.

Conclusion: These authors concluded that dry matter intake, milk and component yields were decreased for dairy cows when fed reduced-starch diets.

Why was this work done and what does it mean? Let’s start at the front end of milk production: the rumen. Properly processed, starches are readily available sources of energy for rumen microbes.

They break down quickly and allow rumen microbes to grow; that growth is about 50 percent true protein, so readily available starches help provide a source of high-quality protein to the cow. When starches are fermented, more propionic acid is produced.

Now let’s go to the final stage of milk production, the udder, and take a look at what’s in milk. First and foremost, there’s water and lots of it; about 87.5 percent of Holstein milk is water. Lactose, or milk sugar, is found at concentrations greater than either fat or protein, and it’s about 5 percent of the total.

Next is fat (3.5 percent), then protein (3.2 percent) and finally ash (0.7 percent). Milk components are synthesized in the udder and are made, in part, from the end products of rumen fermentation discussed earlier in the article.

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Without adequate starch in the ration, rumen fermentation is not as active, compounds required by the cow to make milk and milk components are not as available, and cows make less milk.

Study regarding dietary starch with monensin
Early lactation is a time when cows need everything to be as close to perfect as possible to keep them healthy and promote milk production later in lactation.

M.M. McCarthy, T. Yasui, C.M. Ryan, S.H. Pelton and T.R. Overton of Cornell University, along with G.D. Mechor of Elanco, looked at “Metabolism of dairy cows as affected by dietary starch level and supplementation with monensin during early lactation.”

Cows, either 2-year-olds or 3-year-olds and older, were fed rations that contained either 26.2 percent starch (high) or 21.5 percent starch (low) beginning at calving up to 21 days post-calving. In addition to the high-starch or low-starch treatments, cows were fed either no Rumensin or 450 mg of the product per head per day as part of a top-dress to a TMR.

Cows fed high-starch rations had greater blood sugar (glucose) and less NEFA (free fatty acids) than those fed low starch. During the period from 11 to 21 days after calving, cows fed the high-starch ration had lesser concentrations of beta hydroxy butyric acid (a ketone) than did cows fed the low-starch ration.

Including Rumensin as part of a top-dress increased blood sugar but did not have any effect on NEFA, and beta hydroxy butyric acid was less for cows fed Rumensin.

The authors stated that animals fed high starch after calving and Rumensin throughout the transition period exhibited differences in blood sugar, plasma free fatty acids and liver triglycerides during early lactation when compared to cattle fed low starch and no Rumensin.

Conclusion: As was shown for the first study, there are positive effects of feeding more, but not excessive, starch to milk cows.

Milk production and milk composition were not measured, and the study ended at 21 days in milk. Indices of fat mobilization were measured; these were blood sugar, beta hydroxy butyric acid, NEFA or free fatty acids and liver triglycerides. When cows were fed either high starch or Rumensin, differences in components found in blood or liver indicated cows should be less prone to ketosis.

Study on methane production
Currently, studying methane production in ruminants, and dairy cattle in particular, receives a lot of money and was reported on many times at the conference. While a lot of research money is spent on ways to reduce methane emissions in the U.S., even more money is spent in the EU.

Researchers at the University of Reading in England – K.J. Hammond, D.J. Humphries, L.A. Crompton, P. Kirton, C. Green and C.K. Reynolds – studied the same rations fed to either dry or milking cows and determined, among several items, the amount of methane produced. Cows were fed rations based on either corn silage (maize silage) or grass silage.

Conclusion: Compared to dry cows, lactating cows ate 1.8 times more feed, digested that feed to a greater extent (74.9 percent compared to 72.5 percent) and produced 14 percent less methane per unit of feed consumed.

The investigators stated that difference in methane output between lactating and dry cows may be due to differences in feed intake, which results in difference in rumen function.

It is especially important to note that, when the same ration was fed to different classes of cattle (milking and dry), results were different (more or less methane per unit of feed consumed).

This observation points out that conclusions drawn from any study may only be applicable to that study. A companion paper concluded the results “warranted further investigation.”

The papers we have chosen to review point out that scientific results are seldom earth-shattering and, in fact, the results of all three papers were largely predictable. Scientists are just like professional athletes who work at a task not until it’s done right, but until it’s never done wrong. PD

References omitted due to space but are available upon request. Click here to email an editor.

Carl A. Old
Nutritionist
LeGrand, California

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