Rumen health seminar: Managing acidosis starts with the transitional cow
Ruminal acidosis remains a significant challenge, particularly in early lactation.
Transition cows are particularly at risk due to a temporary drop in DMI that occurs prior to calving and can occur in association with metabolic disorders and/or infectious disease before and after calving.
Decreased DMI causes a rapid and long-lasting impact on rumen absorptive are a, impacting the animal’s ability to balance acid production with buffering, acid absorption and passage.
Transition cows are at an increased risk of ruminal acidosis during early lactation due to a ‘perfect storm’ of low feed intake prior to and at calving, increased feed intake after calving, abrupt dietary change and increased competition for feed, suppressed immune function and inflammation.
It is estimated that 19–26% of dairy cows are affected by sub-acute ruminal acidosis during early lactation and mid-lactation and 12–30% across the entire lactation based on a rumen pH of 5.6.
However, according to a global authority on the subject, Dr Greg Penner, the true prevalence and severity of acidosis is probably even greater.
Dr Penner’s own research shows that the prevalence of sub-acute ruminal acidosis increases markedly during the first 60 days of lactation, peaking at about three weeks.
“Surprisingly, the severity of sub-acute ruminal acidosis during early lactation does not appear to be correlated to increased dry matter intake after calving but rather reduced feed intake before calving,” he says.
“This suggests that other factors, such as the adaptation of the rumen epithelium, rumen microbes and changes in eating behaviour, are involved.
“Feed intake decreases by about 30% during the eight weeks before calving, with about 90% of this happening in the week before calving.
“We need active rumen function (motility) to expose bacteria to feed substrates and then to expose volatile fatty acids to the gastrointestinal tract.
“While not commonly discussed, the rumen wall is a significant supplier of bicarbonate to the rumen via volatile fatty acid absorption and this is significantly higher than salivary bicarbonate.
“Reducing DMI reduces the amount of substrate for the bacteria to work with – and therefore the cow’s ability to absorb volatile fatty acids.
“In turn, low feed intake alters intestinal morphology, reducing the height and width of villi and therefore the absorptive area.
“It takes six to eight weeks to optimise the absorptive area in the rumen and only about five days to negatively impact it, so even subacute ruminal acidosis has a lasting impact on the balance between acid production and acid removal.”
Dr Penner says even a temporary reduction in feed intake can have acute and drastic effects on the gastrointestinal tract.
“Our work has shown that a five-day decline in feed intake can reduce the absorptive surface area in the rumen and the intestine and the size of the rumen, intestine and liver,” he says.
“These are the organs that allow the cow to digest her feed and absorb the nutrients she needs to promote the onset of lactation.
“Any negative impact on gastrointestinal tract function makes the cows susceptible to ruminant acidosis at exactly the same time as feed intake is starting to increase.
“This impairment also increases ‘leakiness’, the ability for bacteria or antigens to cross the gut barrier.” Dr Penner says the goal is to manage cows through the transition phase to minimise insults to the gastrointestinal tract that will cause them to reduce dry matter intake.
“We want to get them off to the races and accelerate dry matter intake and nutrient absorption after calving to support maintenance and lactation,” he says.
“It’s really not about increasing dry matter intake after calving but preventing the negative interactions that will cause a marked decrease in dry matter intake before calving.
“For example, is there feed in the bunk? Is the feed spread out across the whole bunk? Has every cow got access to that feed?
“It’s all about refining your management system to make sure every piece is correct to give those cows the best chance they have to succeed.
“Traditionally, the thinking has been to steamup transition cows up by increasing energy density to make sure we’re meeting their nutrient requirements, despite the reduction in intake.
“We’ve found that actually reduces dry matter intake more as those cows approach parturition, so we can actually make the situation worse.
“We’ve shifted away from those nutrientdense diets more to a controlled-energy type diet.
“We also know that over-conditioned cows have a greater reduction in dry matter intake as calving approaches.”