EBS: Empty bunk syndrome

The health of dairy cows depends on a properly functioning rumen. The ration you feed should focus on providing adequate fiber, energy and protein to feed the rumen microorganisms.

Fortunately the combination of ingredients available to California dairies provides great opportunities to balance these nutrient requirements with economical byproduct feeds. The digestibilities (i.e., extent and rate of digestion in the rumen) of almond hulls, cull fruits, carrots, alfalfa hay, cottonseed, and countless other byproducts, can be combined to create rations that are ideal for rumen fermentation. But the ingredient and nutrient profile of the ration are just the first piece of puzzle that is the feeding of the rumen.

Another piece to a healthy cow is feed management. The difficulties that the dairy industry has faced in the past 18 months have forced changes in feed management practices. While some have been good for your operation, some have not been. The impact of the sum of these changes has the potential to be very costly. To minimize those extra costs, the following three points should be reviewed on your dairy:

1. Are TMRs being sorted?

This is most evident in rations that are relatively drier. Dairies using liquid whey, wet citrus pulps, and/or water have an advantage in this regard. However rations that are high in silages and/or haylage also have advantages.

2. Have you cut back on equipment service?

Over time the cutting knives on feed wagons get dull and eventually wear out. Our observation is that over the past year regular rotation and replacing of the knives have been put off to another day on many dairies. While this may initially save several thousand dollars over a couple of months, an inconsistent TMR for even a few days will be more costly.

3. Do you have Empty Bunk Syndrome (EBS)?

Sometimes EBS is easy to diagnose.  For example, are the cows returning from the milking parlor to empty feed bunks? However, EBS also happens at other times. For example a dairy which was “doing well” with production, but suffering from depressed milk fat %, was visited by one of our consultants one evening who found that about half of the pens were out of feed. He kept this to himself, as he was certain it had to be a rare occurrence, but the next night he observed the same problem. These empty bunks meant that the following morning the cows would “slug feed”, which results in a rapid decline in rumen pH, and fermentation of fiber in the rumen. Although this was probably not the only issue impacting fat test on the dairy, it was certainly a contributing factor.

The challenges of the past 14 months have forced us to be innovative and think outside the box. These two clichés, while overused, are very fitting when discussing rations formulated when high feed costs and low milk price exist. Even though we have tried different approaches to creating rations, the old rules of feed management still apply, and EBS is a good example.

The specific reasons why milk cows have been without feed, especially when returning from the parlor, are not as important as understanding how this impacts rumen function. The semi-continuous fermentation which occurs in the rumen is periodically interrupted by the cow consuming a meal, which causes a decline in rumen pH. Cud chewing, buffers, yeast products, and bunk management are all important factors that moderate this drop but, it is important to keep in mind that this pH decline is going to happen, at least to some extent,  regardless of feed management and additives fed. Your goal should be to make the pH decline as small as possible and for as short a period of time as possible.

Altered rumen fermentation happens due to any stress that causes a change in the rumen environment. Feed quality issues, such as mycotoxins, molds and sorting of TMR may contribute to altered rumen function. All too often, investigations into low milk fat test focus on the technical causes. However, the practical causes are much more likely to be the culprit. For example, why is it that some feed additives known to help moderate the decline in rumen pH fail? Are there other contributing factors which have a much larger impact on the fluctuations in rumen pH? Our feed management audits indicate that EBS is happening far too frequently on dairies and, while the impact of EBS may not be apparent from milk production alone, low milk fat % seems to be the most common affect of an undesirable change in rumen fermentation.

The following is not meant to be interpreted as a “cause and effect relationship,” because milk fat is a blend of more than 20 major fatty acids (the components of milk fat) – so putting too much emphasis on any one fatty acid is risky. However the following discussion is another tool to use when investigating a low fat % situation. Ed DePeters and Peter Robinson (Department of Animal Science, UC Davis), in cooperation with a few nutrition consultants, investigated herds having a fat test persistently below 3.3%, and the results are very interesting. The approach used was to measure the fatty acid composition of milk fat in bulk tank milk samples.

First, a brief review of terminology. Saturated fatty acids have no double bonds between the carbons that make up the chain while unsaturated fatty acids have one (monounsaturated), or more (polyunsaturated), double bonds connecting the carbons in the chain. The position(s) of the double bonds is very important, as will become evident shortly. Another term to know is biohydrogenation, as rumen “microbes” are very good at converting the unsaturated fatty acids to saturated ones (biohydrogenating them) by adding a hydrogen to the carbon at the double bond to remove the double bond.  So:

• Saturated fatty acids, of the form C-C-C-C-C-C-C-C, are chains of carbons with no double bonds. For example, a fatty acid with 16 carbons and no double bonds would be written as: C16:0.

• Monounsaturated fatty acids, of the form C-C=C-C-C-C, are chains of carbons with one double bond. For example, a fatty acid with 16 carbons and one double bond would be written as: C16:1.

• Polyunsaturated fatty acids, of the form C-C-C=C-C=C-C-C, are chains of carbons with two or more double bonds. For example, a fatty acid with 16 carbons and two double bonds would be written as: C16:2.

The investigation by UC Davis examined the fatty acid profile of milk fat from herds with the lower than desirable fat tests. In all cases where fat test was low they found an elevated concentration of a fatty acid called trans-10 C18:1, where the ‘trans-10’ designates the position of the double bond after the tenth carbon in the chain from the carboxyl end and that it has a trans spin orientation (bonds can be either cis or trans). This particular isomer may inhibit fat synthesis and it can be found in milk if rumen function is altered (Figure 1). The pathway for formation of this fatty acid occurs when rumen function is undesirably changed, notably by conditions such as EBS, although dietary factors and feed management that result in low pH in the rumen can result in shifts in populations of rumen “microbes,” which can undesirably alter the biohydrogenation pathway.

The end result may be the same during the biohydrogenation process which produces stearic acid (C18:0; 18 carbons with no double bonds). However, with the altered pathway it is the production of the trans-10, cis-12 fatty acid which is the problem as this fatty acid, even in very small quantities, may substantially lower milk fat production and milk fat %. There are three potential ways in which trans-10, cis-12 C18:2 can become elevated. The easiest to follow is simply ration ingredients. In this case, high levels of free vegetable oils (which are high in polyunsaturated fatty acids) in the ration may simply exceed the ability of the rumen microbes to fully biohydrogenate the unsaturated fatty acids to saturated fatty acids. However, if the rumen environment is such that there is a slowing of the rate of biohydrogenation through the normal pathway, then there may be a shift to the altered pathway. The third likely scenario is the reason for this article. If feed management disrupts the rumen, it can cause a shift in the rumen microbial population. Our feed management audits offer some insight into the impact that feed management is having on rumen function.


The value of these big picture items is improved feed efficiency for each extra pound of feed consumed. Here is some easy math to demonstrate the point.

If you have cows producing 80 lbs of energy corrected milk (ECM) per day at $13.00 per 100 lbs being fed 52 lbs of dry matter per day of a ration which costs $5.50 per cow daily, then each pound of dry matter costs 10.6¢ and income over feed cost is $4.90. However if, due to improved feeding management, you get the cows to eat one additional pound of feed, then this pound raises your feed cost to $5.61 per cow daily. However the additional pound of feed will allow the cows to produce about 2 extra lbs of milk moving your income over feed cost to $5.05. This one pound of feed provides you a good economic return based upon milk alone, and does not consider the improved health of the cow.

Feeding management is one area that has great potential to improve your bottom line, without requiring a high investment.


■  Contact Jim Tully at 209-535-5814.

■  Contact Peter Robinson at 530-754-7565.

■  Contact Ed DePeters at 530-752-1263.