With a wide range of buffers and conditioners being marketed to those looking to improve rumen function, understanding when they are worth using and which factors have greatest impact on efficacy is essential if good decisions are to be made.
Feed efficiency is a high priority for most milk producers at the moment, and efficient conversion of feed into milk is highly dependent on an effective rumen fermentation, says Dr Derek McIlmoyle, AB Vista’s Eastern, Middle East and Africa ruminant technical director.
He adds: “The challenge is that the rumen functions best within a relatively narrow pH range, ideally between pH 5.8-6.2 and the closer to pH 6.0 the better.”
Although an excessively high rumen pH can be just as detrimental as when the pH is low, it is generally the impact of dropping below pH 5.8 (the point at which fibre digestion is compromised) and pH 5.5 (the threshold for sub-acute ruminal acidosis) that is of most concern on-farm.
“Modern, high energy density, early and mid-lactation rations, which contain large volumes of rapidly fermented concentrate, are highly prone to creating overly acidic conditions in the rumen,” explains Dr McIlmoyle.
“The negative effects on rumen function, feed efficiency and milk output – and milk fat production – can be substantial, even if there are no obvious outward signs of acidosis.
“Rumen buffering and conditioning is therefore about much more than just avoiding acidosis.
“It is an opportunity to improve feed efficiency, cow performance and overall margins.”
CONDITIONERS VERSUS BUFFERS
“SLOW-release conditioners have largely superseded the traditional mineral-based rumen buffers, such as sodium bicarbonate, limestone flour and magnesium oxide,” Dr McIlmoyle explains.
“There is evidence that sodium bicarbonate, for example, lowers acid loading in the rumen by increasing outflow rate, resulting in a loss of nutrients and reduced feed efficiency.
“The challenge for end users is that direct comparison under commercial on-farm conditions is extremely difficult.”
Results of a laboratory study comparing the efficacy of 10 rumen buffers and conditioners highlighted significant differences in performance.
The main results of the study are shown in the graph, with the bars indicating the pH at which each buffer or conditioner became active as the pH fell, and inactive as the pH rose.
The zone of optimum rumen function (pH 5.8-6.2) is shown as a green shaded area, while the threshold for clinical acidosis (pH 5.5) is highlighted by a red dashed line. Only one product produced a result within the optimum zone.
“More than half failed to become active until the pH was well below the threshold for acidosis, while two produced results that indicate the potential to push rumen well above pH 6.2,” Dr McIlmoyle says.
There are also significant differences in capacity to neutralise acid within the rumen. A separate comparison between two of the leading conditioners on the market found an 88 per cent difference in acid neutralising capacity.
“The research highlights just how important it is to ask your supplier the right questions about the activity threshold, known as the average ionisation pH, and acid neutralising capacity,” Dr McIlmoyle adds.
Other factors to consider include a high surface area (which can improve a conditioner’s ability to neutralise acid) and whether it remains inactive until in the rumen.
According to Dr McIlmoyle, much of the acid neutralising capacity of mineral buffers can be used up in reaction to acid in the silages within the ration, leaving them much less effective in rumen where most of the acid is produced.
“The more efficient conditioners will generally be the most costeffective, with greater efficacy enabling dose rates as low as 80g/cow/day, compared to about 250g/cow/day for sodium bicarbonate,” he highlights.
“Some also contain highly bioavailable minerals, such as calcium and magnesium, which can contribute to meeting cow requirements and allow other mineral sources to be reduced.”
ASSESSING RUMEN CONDITIONS
ACCORDING to Dr McIlmoyle, whenever there is potential for rumen pH to move outside the pH 5.8-6.2 range for a prolonged period of time, the use of a buffer or conditioner is worth considering.
“If rations are pushing the limits of what the rumen can withstand, the chances are that rumen fermentation efficiency is already compromised,” he says.
“Research at University College Dublin showed that even when no specific acidosis threat was present, feeding a slow-release rumen conditioner can increase milk solids production by up to 7 per cent and energycorrected milk yield by as much as 1.74kg/cow/day.”
Dr McIlmoyle’s advice is to assess the level and type of pressure the rumen is under, using the values in table (above) to allocate a score for the six assessment categories listed, depending on whether each represents a low, medium or high risk factor.
The total can then be checked against the information at the bottom of the table.