The following case study was a senior project by a student in the dairy science department at California Polytechnic State University in San Luis Obispo, Calif. This is a short summary of the paper.

A major diarrhea outbreak occurred simultaneously with a 15-pound decrease in milk production at a dairy in California’s central valley.

Potential causes included silage quality, disease, water quality, almond hulls containing high levels of mycotoxins, and feed-ration issues.

Regarding disease, investigators looked at possible infectious causes like salmonella, bovine vital diarrhea virus, winter dysentery and corona virus. The latter two were immediately ruled out since their symptoms were different than what was seen in the herd. That left salmonella and BVD, but lab samples came back negative for both diseases.

Water quality was another issue. There were some problems here, including high chlorine and a brief interval where rust-colored water from a backup well was introduced into the system and got into the water troughs.  

Then there were the almond hulls. Shortly before the outbreak, it had rained and water formed a puddle around the base of the almond hulls. With new loads of almond hulls coming in, a small amount of wet almond hulls was stuck at the bottom of the pile and given the opportunity to form molds. A lab sample of the affected hulls showed high levels of aflatoxin and zearalenone. But since the affected hulls were only fed in small portions for several days, could that have caused a problem that lasted for 11 weeks?

Suspicions still centered on forage quality. Samples indicated high ash content in two sorghum piles ― likely the result of poor chopping practices. And a corn silage pile had two specific issues:

  • It was poorly packed
  • It contained corn of unequal quality from two separate farms.

Six to 8 feet of hot and moldy silage was removed from the top layer of the corn silage pile after it was opened up; fortunately, the lower half of the pile was tested to have good quality.

The final rule-out was the TMR. The ration was changed many times throughout the duration of the problem in hopes of firming up the loose manure and gaining back milk production. That, along with the silage problems already noted, may have contributed to sorting  and inconsistencies in nutrient intake. Finally, there were problems with the energy/protein balance in the ration.

At the end of the day, no single cause stood out; rather, it appeared to be a perfect storm of several destructive events occurring at once.