Is your zinc working?
We are coming into the Facial Eczema (FE) season once again and typically we all look to monitor the spore counts to ensure we get our zinc going through before the spore counts jump up… but how do we know that we are giving enough?
Often when we see issues arise despite treating with zinc it isn’t due to the spore counts being overwhelmingly high, it’s due to our zinc dosing being inadequate. This can be due to a multitude of reasons that include (but aren’t limited to):
- Dosing to average liveweight (some cows bigger some smaller)
- Dosatron not working correctly
- Form of zinc being used, and dose rates required (i.e. Hepta vs Mono vs oxide)
- Leaks in the water system
- Weather conditions
- Miscalculation of zinc offered
- Mixing of feed in feed pad delivery systems
- Inclusion in in-shed feeders being incorrect (i.e. not added to the pellet or blend properly)
- Not accounting for feed wastage
There have been a variety of studies now that show significant variability in blood levels despite treatment choices (Mason and Cuttance 2016, Morris et al 2013, Ruakura 2009) with evidence showing that up to 44% of cows had blood levels of zinc below the target!
So how do we know we are achieving what we set out to in the first place? The important aim for what we are doing is to achieve circulating zinc levels 20-35umol/L in blood, this can be tested for by taking 10 cows 2-3 weeks after implementation of full rate supplementation programs to check how you are getting on, this will answer the question “are your cows getting enough zinc”? If you are not achieving the required levels then we can look at how this can be achieved.
In addition to this, when the spore counts are on the rise and we are wanting to make sure that it is being effective then it is a sensible move to check, testing 10 animals for GGT levels will enable us to determine the effectiveness of the program (its efficacy). In order for us to be able to do this effectively it is important that there is suitable potential exposure to FE, so this needs to be after the spore counts for the area have exceeded 20-30,000 for a period of 2-3 weeks.
GGT is the acronym for a liver enzyme that will rise in response to any damage done to the liver, measuring GGT levels will expose the sub-clinical disease that may be occurring and will help to dispel any complacency that all is well just because there is no clinical evidence of FE.
Hopefully you all have a plan in place for your management of FE this year but if in doubt please contact your vet to discuss. It is worthwhile to test your cows and make sure that what you are spending your money on what is going to be effective!