Dietary ingredients that producers feed to dairy animals determine their efficiency and health status. In order to produce more milk, concentrates have gained popularity as an energy source for increased milk yield.
However, high-concentrate diets have been known to have negative side effects such as decreasing rumen pH and potentially causing subacute ruminal acidosis (SARA).
SARA has been defined as rumen pH below 5.6 for more than three hours per day. It’s important to understand the natural rhythms of rumen pH in order to realize what the detrimental effects of high concentrates might be. Naturally, cows will experience fluctuations in rumen pH from 6.4 to 6.6, with the lowest pH happening directly after feeding.
As rumen pH becomes more acidic, the rumen microbial population changes, thus changing the nutrients cows will receive. Consequently, cows experience stomach upsets and decreased feed intake, which will decrease milk yield, and since the rumen microbial population has now changed, it will alter milk composition.
Cows can also experience diarrhea, laminitis or rumenitis, which may even result in higher culling and death rates.
SARA has been estimated to affect between 19 and 26 percent, at times reaching 40 percent, of dairy cattle in early to mid-lactation. An estimated $400 per cow per lactation on milk loss alone can add up to even more with more severe cases for dairy farms throughout the U.S.
Clay buffers have been used to prevent ruminal pH decreases, while at the same time not allowing pH levels to rise too high, either. There are many structurally different clays available to be used as a buffer; however, they all possess the same quality – the ability to exchange cations. This capability gives the product the aptitude to capture charged ions within the clay structure to maintain pH.
In order to further investigate the potential use of clay to alleviate the effects of SARA, we developed a study at the University of Illinois. Ten cannulated Holstein cows were used in an experiment to determine the effects of the clay after a grain challenge on ruminal, blood and fecal pH as well as milk composition.
The experimental design was organized so that all 10 cows went through each of the five treatments for a 21-day period with a challenge for a total of 105 days.
Treatments were: NEG – no clay in the diet and no challenge; POS (0 percent) – no clay with a challenge, 0.5, 1 and 2 percent of the dietary dry matter intake (DMI) as clay with a challenge. The clay was weighed daily and mixed with 1.1 pounds of grounded corn and top-dressed onto the TMR.
From day 1 to 18, cows were fed once daily ad libitum. On day 18, cows were fed only 75 percent of their average DMI from the three days prior.
On day 19, cows were given the grain challenge using 20 percent finely ground wheat flour, based on the average DMI obtained from the three days prior, and then offered 100 percent of their TMR. Rumen pH and fecal pH were taken at zero, four, eight, 12, 24 and 48 hours relative to grain challenge.
Blood samples were taken at zero, 16, 24 and 48 hours post-challenge.
The exact mechanisms of clay products are unknown; however, it has been widely proven that buffers decrease propionate, leading to an increase in ratio of acetate to propionate. Acetate production by the rumen microbes has been positively correlated with milkfat.
In our study, cows receiving clay in the diet increased milkfat from 2.2 pounds per day to 2.8 pounds per day. It can be postulated that the clay product being tested aids microbial populations to decrease propionate while at the same time increasing acetate.
Decreasing DMI was one of the side effects mentioned when feeding high-concentrate diets, but in this study cows did not alter their DMI. In fact, cows receiving the clay in the diet increased their milk yield from 61.1 pounds per day to 66.6 pounds per day.
Fat-corrected milk (3.5 percent) increased from 62.6 to 75.1 pounds per day for cows receiving the clay during the challenge.
Other studies have reported increases in milk yield and DMI when being fed other types of buffers. In our study, there were no differences in blood pH or other blood parameters.
The physiology of the cow is to maintain blood pH at 7.4, and cows in the POS group reached the lowest blood pH at 7.33.
Interestingly enough, cows receiving clay in the diet had a linear increase in O2 saturation. It has been found in some clay structures that there is a fraction of extractable iron oxides.
These iron oxides potentially could be absorbed by the cow, which would explain the linear increase in O2 saturation with iron.
Fecal pH followed the patterns of rumen pH, indicating that there was enough starch bypassing the rumen to alter fecal pH. Cows in this study were in a state of SARA due to the rumen pH being below 5.6 for more than three hours.
Cows receiving clay in the diet reached the lowest rumen pH of 5.06, whereas cows not receiving clay reached lowest rumen pH at 4.94. Overall, rumen pH was 0.13 higher and cows spent an average of 1.8 hours less time under rumen pH of 5.6 for cows receiving clay during the challenge.
This study demonstrated that clay in the diet has the ability to alleviate negative side effects of a grain challenge (SARA).
A positive linear treatment effect (from clay at 0 percent [POS] to 2 percent of dietary dry matter) on rumen pH indicates that clay at 2 percent had its maximum buffering capacity and consequently reduced the time cows experienced rumen pH below 5.6 after a grain challenge. PD
Yuri Khidoyatov is the business development manager for United Minerals Group.
Phil Cardoso is an assistant professor with the University of Illinois Department of Animal Sciences.
Saige Sulzberger is a M.S. student at the University of Illinois.
