Dairy producers frequently add clay as a feed
supplement to reduce the symptoms of aflatoxin and subacute ruminal
acidosis (SARA) in lactating cows. In a new study from the University of
Illinois, researchers show that clay can also improve the degradability
of feedstuffs.
"Farmers are giving this clay, but they want to know if the corn
silage or hay the cow is eating is affected. We found that yes, the clay
is changing the way the cow degrades feedstuffs," says Phil Cardoso,
associate professor in the Department of Animal Sciences at Illinois and
co-author of the Animal Feed Science and Technology study.
Cardoso and his team tested the degradability of six feedstuffs -
dried alfalfa hay, grass hay, wet brewer's grains, ground corn, corn
silage, and soybean meal - along with no added clay, 1%, or 2% of
dietary dry matter.
The researchers placed the feedstuffs into mesh bags and inserted
them directly into the rumen through a cannula or fistula, a surgically
installed portal that allows the contents of the rumen to be sampled for
research purposes. The bags were then drawn out at multiple time
intervals (two hours to four days) and analyzed.
"There were some differences in how the feedstuffs degraded over
time. When clay was added to grass hay at 2% of dietary dry matter, the
digestibility and usage of the fat in that material was maximized. It's
better. And we didn't see a decline in degradability of the other
feedstuffs, either," Cardoso says. "Overall, to maximize the benefits of
clay, we'd recommend adding it at 1 to 2% of dietary dry matter."
Cardoso's previous research has shown that multiple types of clay
are effective in handling aflatoxin, a toxic substance produced by
fungal contaminants on feed. When the toxin is bound up by the clay, it
is simply excreted from the cow's body, rather than being absorbed in
the bloodstream. And a 2018 study by Cardoso's team showed that
aluminosilicate clay improved cows' immune function and reduced liver
inflammation during an aflatoxin challenge.
Cardoso says, "From all of our work on this, I can tell producers
whenever they are facing the risk of aflatoxin, they should consider
using clay without worrying about it binding other minerals or hindering
forage digestibility. Rather, we've shown digestibility could increase.
Of course, it's important to ensure the specific clay product has been
tested."
Clay's benefits don't stop there. Because the material attracts and
binds positively charged ions, clay can make the rumen less acidic. This
is important particularly given the popularity of increasing grain
concentrates in TMR feed, which can lead to SARA. In a 2016 study from
Cardoso's group, cows challenged with excess wheat in a TMR diet
produced more and higher-quality milk and had higher rumen pH when fed
bentonite clay at 2% of dietary dry matter.
"Basically, clay has all these benefits: It reduces aflatoxin
toxicity, works as a pH buffer, and also improves the degradability of
some feedstuffs," Cardoso says. "Producers should know this."
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