It might not be an exact science, but the barnyard and boot study of manure is a simple reflection of the dairy diet being fed, how it is consumed, digested and finally pushed out onto the alley. When dairy cows defecate, we can get a pretty good idea as to their nutritional status by observing manure colour, consistency and content. If one of these parameters is out of line, necessary changes might be made to the cows’ diet for better manure, which can lead to improvements in overall dairy health and performance.
A 600-kg milk cow in lactation produces up to 70 kg of fresh manure per day, which contains both digested and undigested feed that pass through the rumen, and the rest of gastrointestinal tract. It also contains a mixture of digested rumen microbes, rumen fluid, bile and other digestive juices together with large volumes of drinking water as well as recycled body-tissue water before it is finally excreted.
During a barn-walk, one of the first general rules of manure evaluation is that given a group of dairy cows, which are eating the same dairy diet, most should produce manure of similar colour, consistency and content. A small fraction of cows (less than five per cent), for various reasons will have significantly different-looking manure compared to the general cow herd.
Regardless of our initial impression, what manure we actually see will most likely come from a relatively modest sample of dairy cows. It is recommended that we look at the manure of between five and 10 per cent of the cows to make our observations and draw some conclusions. For example, we should choose 15 to 20 cows from a 200-cow dairy to get this general consensus. It is also a good idea to move along the fresh pies and poke a few with a boot to get a good idea of manure content.
For many dairy producers and specialists, the first observation of a freshly dropped cow pie is its consistency.
Manure consistency is a good indicator of the digestion status in dairy cattle. It is dependent upon feed type, nutrient and dietary fibre content, water intake (and quality) and digestive passage rate. A normal manure consistency should be porridge-like and when the animal defecates it should produce a slightly dome-shaped pile. Relatively loose manure can range from a slightly rapid passage of manure through the cow to extreme water-like diarrhea. At the other end of the scale, thicker manure can look firmer, drier and possibly make taller piles.
In cases of loose manure, some of its origins often start with dairy diets that are formulated with too much soluble protein or diets that do not contain enough effective forage fibre in order to produce a good “forage-fibre mat” in the rumen. These are two of more common conditions from a possible longer list of causes that speed up the passage of feed throughout the gut and cause loose manure. To correct these common situations, some producers either decrease the soluble protein of the diet by lowering the amount of high quality forages fed or adding one-half kilo of straw, accordingly.
Other cases of loose manure are far more serious and their actual causes seem to be harder to pinpoint. For example, sub-clinical acidosis (SARA) causes loose manure consistency to vary amongst herd members as well as other multiple changes over time for each suffering cow.
Unlike high dietary-protein diets, which can cause loose manure in all herd members, manure from SARA cows is equally loose, but pasty, shiny (re: intestinal sloughing) and contains small bubbles. As each affected cow goes through a typical “off feed-on feed” cycle, its SARA manure may disappear and can be temporarily replaced by more solid-looking manure. Unfortunately, as the SARA conditions return; rumen acid levels start to rise, water is then brought back into the gut in order to neutralize them and the shiny loose manure begins again. It is this state of manure inconsistency that dairy producers might identify a prevalent SARA problem in the herd.
In similar acidosis and extensive hind-gut fermentation situations, mucin casts (fibrin-tissue) may also be found in such abnormal manure. They are secreted into the gut in order to cover up extensively damaged areas. It should be recognized that sloughed-off mucin casts might be found in manure of any consistency.
WHAT ABOUT CONTENTS?
Just as manure consistency can tell how feed is being digested in the cow, the contents of manure can also tell producers what is working or may not be working in the dairy diet.
Manure that is produced from cows fed a well-balanced nutritious ration (with adequate effective fibre) is very uniform. It contains digested feed particles with the majority of processed forage fibre no greater than 1/2 inch, and with little escaped grain. If a cow pile is littered with long-stem fibre or large amounts of grain, it could be a sign of inadequate dietary effective-forage fibre, unprocessed added grain, or even the possibility of forage (i.e. silage) harvested in an extreme state of maturity.
THE COLOUR STORY
Compared to cow pie observations of consistency and content, the “normal” colour of manure offers some, but limited valuable information as to how feed is being digested. Manure colour usually reveals the type of diet being fed to the cows.
As expected, high-hay or haylage diets tend to produce dark green manure, while corn or barley silage produces brown manure. Likewise, rations with high grain content tend to produce relatively light-coloured manures. When feed is going through the animal at a particularly high rate, it may turn into an unusual green/brown-grey colour. A rapid colour change may signal that something is amiss with the cows’ present ration. †