RUMINANTS
Subclinical copper toxicity in Ontario dairy cows
Brent Hoff, Nick Schrier, Beverly McEwen
Chronic copper toxicity has classically been associated with chronic overprovision of copper (Cu) to sheep. There and only a few reports of similar cases in cattle, suggesting that cattle have some degree of resistance to Cu toxicity.
An increasing frequency of Cu toxicity has been reported in European dairy cattle. Pathologists from Minnesota and Wisconsin report several cases of subclinical Cu toxicity in high-producing Holstein dairy cows, with clinical signs of infertility and ketosis refractory to treatment with propylene glycol. Cases had diffuse hepatocellular vacuolation, random, single-cell necrosis, biliary hyperplasia, and mononuclear inflammation with levels of Cu >150 ppm wet weight (ww) (normal reference interval 25-100 ppm) in livers. When the liver is damaged, energy mobilization and the cow’s ability to adapt to negative energy balance changes, with the main impact on fertility and possibly milk yield. Liver damage, as determined by elevated serum levels of the leakage enzyme glutamate dehydrogenase (GLDH), began at 150 ppm ww of Cu in the liver, and decreased following withdrawal of dietary Cu. It has also been reported that dietary supplements leading to Cu accumulations in the liver at concentrations only slightly above normal levels (~125 ppm ww) caused reduced feed intake and average daily gain.
Subclinical Cu toxicity is often difficult to detect, and may be a more frequent problem in high-producing dairy cattle than the minimal number of clinical cases would indicate. Low serum Cu is of some value in chronic deficiency of non- supplemented beef cows, as the hepatic Cu has been depleted, but is of no value in supplemented daily cows. Unfortunately, only assays on liver biopsies from high-producing dairy cows will confirm elevated Cu levels because the association between serum Cu and liver Cu is poor.
Review of AHL ICP-MS trace mineral analyses on liver of 102 adult cows revealed a mean Cu of 118 ± 66 ppm ww (normal reference interval 25-100 ppm ) with 25 samples >150 ppm with a mean Cu of 205±74 ppm.
Liver biopsy samples are an especially good means of assessing Cu status. They are also very useful in assessing selenium status and histopathology. We can measure trace mineral concentrations in very small liver biopsy samples that can easily be taken using a “Tru-Cut” type biopsy instrument. These small samples can be placed in the bottom of a small nylon container and quickly frozen. The liver biopsy procedure can be found in LabNote 19 on the AHL website: https://www.uoguelph.ca/ahl/ahl-labnote-19-liver-biopsy-procedure-cattle
Changes in the cutoffs for milk and serum Johne’s antibody tests
Jim Fairles, Davor Ojkic
Cow milk samples tested for paratuberculosis (Johne’s disease) by Canwest DHI and serum samples tested by the Animal Health Laboratory at the University of Guelph use the same IDEXX ELISA kit. Recently, IDEXX revised the cut-offs for negative, suspect and positive test results. These changes are intended to increase the sensitivity of the test slightly, and will take effect December 1, 2015.
The table below includes the new cut-offs for both milk and serum, as well as the old cut-offs for comparison. The cut-off for a high-positive test result in both milk and serum remains unchanged at sample-to-positive (S/P) > 1.0.
