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Uncovering the value of pectins

Digestible fibre is a critical component in all ruminant rations, helping to buffer against acidosis and optimise rumen function, as well as supporting milk fat production. And whether it’s making up the shortfall in lush spring grass, balancing high-starch beef and dairy rations or promoting milk solids production in lactating ewes, the use of specific digestible fibre-based feeds like sugar beet feed, soya hulls or citrus pulp is now common practice.

But according to Trident technical manager Dr Michael Marsden, when it comes to achieving the positive effects on rumen fermentation that we traditionally associate with digestible fibre, it’s not as straightforward as it seems.

“In addition to digestible fibre, most livestock feeds also contain other feed components called pectins that can have similar beneficial effects,” he explains. “Unfortunately, the measure of digestible fibre used in the UK – neutral detergent fibre, or NDF – doesn’t include the pectin content.”

This is in contrast to the feeding and ration formulation systems used in the United States, where pectins are measured, and included when calculating overall digestible fibre content. The challenge for UK farmers and nutritionists is that certain digestible fibre feeds produce a better rumen fermentation and animal performance than their basic UK proximate analysis would suggest, it appears to be the pectins – along with differences between the digestible fibres themselves – that are responsible.

“The problem is that although pectins play a crucial role in both energy supply and rumen buffering, they’re hard to measure and relatively poorly understood,” continues Dr Marsden. “As a result, they’re not included in any of the measurements we use to determine feed value in this country, and are generally ignored during ration formulation.”

Table 1 shows the results of a pair of trials from the United States where a proportion of maize grain (starch) was replaced by digestible fibre energy in the form of either sugar beet feed or citrus pulp. As expected, butterfat percentage increased in both trials, but the sugar beet feed produced a much greater milk fat response (+0.18 versus +0.05 percentage points) and was also able to maintain milk yield despite having a lower energy content than the maize.

Table 1 – Impact of digestible fibre source on milk production

“A large part of this response appears to be due to the pectins, which ferment to produce the same acetate that’s produced from digestible fibre, and which is a key building block for butterfat production in the udder,” Dr Marsden states. “It’s just produced from pectins much more quickly in the rumen.”

More importantly, the microbes that ferment pectins are also highly sensitive to acidity. If acid levels in the rumen begin to increase and pH falls, pectin fermentation slows, only rising again when a proportion of the excess has been absorbed through the rumen wall and pH begins to return to normal.

“It’s the perfect feedback loop, naturally buffering the pH of the rumen, and is very different to the situation for starch fermentation, where the microbes involved are more than happy to keep going as the pH drops,” Dr Marsden states. “It’s why feeds like sugar beet feed that are high in pectins perform better than simple proximate analysis would suggest, with the lower energy content in the trial mentioned earlier (Table 1) outweighed by the improvement in rumen fermentation efficiency.”

Most concentrate feeds contain less than 3% pectins in the dry matter. However, digestible fibre feeds tend to contain much higher levels, and although the analysis is somewhat inconsistent, best estimates put the pectin content of sugar beet feed at 35%, soya hulls at 24-26% and citrus pulp pellets at 15%.

“The sheer amount of pectins that appear to be in some of these digestible fibre feeds, plus the important role they can play in maintaining a healthy rumen, means that pectins really shouldn’t be ignored,” concludes Dr Marsden. “So when it comes to balancing high levels of starch-based concentrates, supplementing lush spring grass and maximising the efficient conversion of feed into growth or milk, it’s not just digestible fibre that you should be thinking about.”

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