Farming Magazine - January, 2012


Dairy Nutrition: More Efficiency

By John S. Hibma

These days you don't go very far without seeing something on TV or hearing something on the radio or reading something in a magazine or newspaper about how critical it's becoming that we conserve our precious natural resources. We're encouraged not to waste or misuse both for altruistic and economic reasons. We need to be both frugal and efficient with the resources we have available to us.

I'm writing this a few days after the monster Halloween weekend snowstorm of 2011 has left behind its massive carnage in the Northeast. Locations in Connecticut and Massachusetts may be (optimistically) without power for a week or more. Hopefully I'll have hot water back in my house by the time you read this. Since I have a well on my property, when the electricity goes I lose my water, too. So I've been trudging back and forth to my neighbor (who's on municipal water) carting buckets of water back to my house so I can do a few things like flush the toilets and wash a few dishes. My wife and I quickly learned to become very frugal and efficient at managing our meager water supply.

For many years already, the dairy industry has been facing the necessity of being frugal with feeds and managing and maximizing feeding efficiencies in dairy herds. With soaring grain prices, dairy farmers are being urged to do the most they can with the forages available to them, whether homegrown or purchased. Properly grown, harvested and stored, forages offer the potential for a dairy farmer to reduce the reliance on purchased feeds. A second option is to design feed programs that maximize the milk production potential with the use of grains and forages together.

In the Northeast, corn silage is the primary forage fed to dairy herds. Corn silage has the dual functionality of being both a forage and a grain when ears are abundant on the cornstalk. There are many farms that produce exceptional corn silage with lots of grain. One of the potential problems with corn silage that's loaded with lots of grain, however, is that cows can suffer from varying levels of rumen acidosis due to the high starch content of the corn silage - especially if a grain mix already has a lot of corn in it.

Rumen acidosis occurs when there are too many rapidly fermented carbohydrates in a cow's diet. Most of the time, the culprit is the starch coming from the grain. Dairy farmers feeding corn silage with high starch levels may also overload their cows' rumens with those rapidly fermented carbs. High feed intake of rapidly fermentable carbohydrates increases acid production in the rumen. Prevention or elimination of rumen acidosis requires balancing the production of those rumen acids and the neutralization or removal of them. Neutralization occurs through buffering (mainly salivary buffers), absorption through the rumen wall and passage from the rumen.

Dairy cows regularly run into trouble with acidosis even in the most well-managed feeding regimens. In a Florida study, the rumen pH of a cow was tracked over a period of about four days. Subacute rumen acidosis (SARA) for that cow (pH 5.8) occurred for 6.4, 6.5 and 11.8 hours per day on August 5/6, 6/7 and 7/8, respectively. Arrows show feeding times at 13:30 and 16:00 hours; the solid line indicates the rumen acidosis threshold of pH 5.8. During the course of the four days the pH in the rumen fluctuated from just under 7 to just above 5 - sometimes in just a few hours. This variability of the pH makes it nearly impossible for rumen microbes to maintain any consistency in the fermentation of feedstuffs. Hence a dramatic drop in rumen fermentation efficiency and milk production.

Rumen acidosis decreases the digestibility of fiber in the rumen, which decreases feed conversion efficiency and increases feed costs. This reduction in potential fiber digestion is equivalent to a loss of 5.5 pounds of milk per day. Acidosis can also cause erratic fluctuations in feed intake. Extended periods of low rumen pH cause a cow to go "off-feed," reducing the microbial efficiencies and the conversion of feedstuffs into energy and milk. Repeated bouts of subacute acidosis can damage the surface of the rumen wall, causing the cow's immune system to respond with toxins that lead to laminitis.

Along with the potential for acidosis caused by excessive starch in a diet, the newer, highly digestible corn silage varieties are also prone to not meeting the physically effective fiber needs of the rumen. Long forage particles in the diet promote chewing and salivary secretion, which helps buffer the acids resulting from feed digestion. Thus, particle length of forages and the amount of fiber in the diet can have a significant impact on rumen pH by way of salivary buffers. Long particle forage causes the cow to spend more time eating and ruminating, which increases the flow of salivary buffers into the rumen. In addition, long forage fiber creates a floating mat in the rumen, which stimulates contractions of the rumen. Without these mixing motions the rumen can become a stagnant pool, thereby increasing the risk of acidosis. Fiber is more slowly digested than starch and sugar, so the inclusion of fiber in the diet slows the rate of feed digestion in the rumen.

I recently wrote in this column about the Penn State Forage Separator being a useful tool for adjusting dairy diets to meet adequate physically effective fiber requirements. While dairy farmers are encouraged to maximize forage quality and usage in dairy diets, sometimes that forage can be counterproductive when a dairy farmer unknowingly causes rumen acidosis, especially with corn silage that acts more like a grain than a forage.

Closer attention must be paid to formulating diets as we tighten them down in pursuit of lower feed costs, often putting cows precariously close to rumen acidosis and poor feed conversion efficiency. To maintain rumen efficiency in today's economic environment a dairy cow's diet has to be balanced just as accurately from a physical-fiber point of view as well as the chemical-nutritional point of view.

Note: Some of the information for this article was taken from the 2007 Florida Nutrition Symposium: "Ruminal Acidosis in Dairy Cows: Balancing Physically Effective Fiber with Starch Availability," K.A. Beauchemin.

The author is a dairy nutritional consultant and works for Central Connecticut Farmer's Cooperative in Manchester, Conn.