There are so many things we can do with manure today. We can look at it, smell it, kick it, stomp it, get showered in it (never stand behind a cow while she coughs and defecates simultaneously – guilty), burn it, spread it, make garden tea bags with it, compost it, sell it, watch a client swim in it (after a cow decided to take a suicidal dive into the lagoon) lay in it, and as a vet we are forced to say spread disease with it. But what can manure tell us about the cow and about the general health of the herd?
A typical cow produces about 150 pounds or around 20 gallons of manure daily and passes manure every 1.5-2 hours so we have plenty of manure to analyze. A normal manure pile will stand about 1 to 2 inches tall with a slight dome shape and dimpling. Preferably, notable feedstuffs and forages should not be recognizable within the manure. Manure characteristics across the herd should be similar with very little variation among individuals. What causes manure variation and deviation from the norm?
During herd checks, we put our hands, eyes, nose, and boots to good use. We typically make comments regarding the consistency of the manure. “The cows are too loose today.” “Wow, that stack is a foot high!” Consistency is normally associated with water content in the manure which is highly dependent on water consumption or transit rate through the digestive system. The longer the transit rate, more time is available to absorb water. Dry, highly stackable manure is seen in cows lacking adequate water or protein consumption and/or consuming a high fiber ration. Remember that cows require 3.5” per head water trough space and a palatable water supply. Cows with a displaced abomasum or disease that hampers feed consumption will decrease fecal output and have drier, pastier manure. These individuals require a physical exam.
When many cows exhibit signs of loose manure or diarrhea, in addition to addressing ration concerns, infectious disease must be ruled out. Infectious causes of loose manure include Salmonella, Winter Dysentery (Coronavirus), BVDV, and Johnes. Parasites, such as coccidia and worms, must be considered, especially in poorly grown heifers. The odor significantly changes with infectious causes of diarrhea as well.
In general loose manure consistency is associated with excessive rumenal feed passage rate. As manure leaves the cow, keep this phrase in mind, “The broader the arch, the more serious the gastro-intestinal insult!” Passage rate speeds up with high dry matter intake and slug feeding, sorting and consumption of rations lacking effective fiber, excessive protein intake with high rumenal degradable protein (cows on lush spring pasture), and rations high in non-structural carbohydrates. Depressed or severe fluctuations in rumen pH are common. Hyper-excitable cows, stressed cows, and cows under heat stress resulting in high water consumption, feeding slugs, and lower rumen pH will also lead to higher passage rates. Disruptions in the rumenal microbial population from depressed rumen pH or acidosis, mycotoxins, poorly fermented forages (high yeast, mold, clostridium), etc will also impair rumenal fermentation and may lead to loose manure.
As rumenal transit rate increases, feed typically fermented in the rumen, passes unfermented out of the rumen. Digestion and absorption occurs in the small intestine, but with excessive passage rates, the small intestine is overwhelmed. Undigested feed ends up in the cecum and large intestine or hindgut where additional fermentation and nutrient absorption occurs. When the large intestine becomes overwhelmed with excessive hindgut fermentation and passage rate, feed passes in the manure undigested and other health problems will ensue.
Manure content changes with higher rumen passage rates. For a qualitative assessment of manure, use a kitchen strainer 7” wide and 4” deep with 1/16” or 1.66mm openings and rinse with water until the water runs clear. Commonly you find undigested feed and fiber, undigested ground grain less than 0.25”, and fiber length exceeding 0.5”associated with high passage rates. The feed passes the rumen before adequate fermentation and rumination can occur. For instance, cottonseed with lint may be passed. In other cases, undigested grain passes in the manure due to poor forage harvesting or grain grinding methods. In most cases, the physically effective NDF is lacking in the ration providing an inadequate rumen mat. Herds lacking physically effective NDF will see a higher incidence of mid- to late-lactation DA’s
Additional screening techniques can be utilized. Use a Penn State Particle Separator to ensure you have adequate top (6-10%) and middle screen (30-50%) TMR percentages. Fecal starch analysis could also be used to assess passage rate issues. Goal fecal starch levels <5% are preferred with 2-3% considered optimal. Forage 30-hr NDF-digestibility should also be monitored at least monthly especially in herds feeding highly digestible corn silage. With higher NDF digestibility, passage rates have the potential to increase. Hay or straw is commonly added to the ration to provide additional peNDF and also to maintain a “scratch factor” source during forage changes when digestive upsets are most likely to occur. Ensure that hay or straw sources are processed to a 2” length to prevent sorting. At the same time, do not over-process forages with short particle size.
Mucin (mucous strands in manure) or fibrin casts and foamy/bubbly manure are found in cows with high passage rates along with excessive hindgut fermentation. Fermentation produces organic acids and gas – methane and carbon dioxide. Fermentation in the rumen is more valuable than fermentation in the large intestine because fewer nutrients are absorbed in the hindgut. In the rumen, the cow buffers acid with saliva and eructates to remove gas. The hindgut lacks these systems. As a result, the excessive acid production irritates and damages the intestinal lining resulting in mucin and fibrin cast production. Gas passes in the manure as bubbles and froth or foam.
With excessive passage rates and fermentation, cows are also at greater risk for developing hemorrhagic bowel syndrome (HBS) or jejunal hemorrhage syndrome. The conditions are ripe for clostridium perfringens type A overgrowth and toxin production and along with the presence of the mold, Aspergillus fumigatus, hemorrhage occurs in the intestine. Characteristic of HBS, manure is either pasty red or grape jelly in color and consistency from blood clots formed in the intestine. In advanced cases where death is imminent, no manure is typically found.
Further upstream, acidosis and stress can induce abomasal ulcers. Unlike the grape jelly or reddish coloration of HBS, cows suffering from abomasal ulcers produce black and pasty manure. Blood clots are more digested compared to blood resulting from HBS. Blood clots are digested first in acid and then the intestines resulting in black manure.
Infectious causes of diarrhea produce interesting manure characteristics. Blood and mucous are found in the manure of animals infected with winter dysentery, salmonella, and coccidia. Sloughed intestinal lining and fibrin are also found in more severe cases. When cows appear to be passing snakes or snakeskins, your herd has serious health problems!
When troubleshooting manure variation and herd health problems, carefully assess manure consistency and content. “Passage rate” was mentioned often to emphasize that causes of higher passage rate significantly impact manure characteristics. Work closely with your nutritionist and veterinarian to determine the underlying source of higher passage rates and herd health problems