Fiber isn’t fiber isn’t fiber. Lots of folks talk about fiber – doctors, teachers, marketers, nutritionists – but there are different types of nutritional fiber, and fiber digestibility partially depends on the species of animal consuming it. Things quickly get complicated. This month, let’s talk about a fiber of contradictions – pectin – which has the digestible energy of starch but doesn’t act like starch in the rumen and doesn’t even show up in a fiber analysis. But it can be used to fatten cattle. Interested yet?
Pectin is one of those words we’ve all heard for years. Companies extract it commercially from apple pomace and citrus peels, and it’s used extensively in many human feeds, er … foods. Cooks use pectin to thicken liquids, especially jams and jellies. They use it as a stabilizer for liquids like juices and protein drinks, and as a substitute for fat. It’s used in medicine for drug preparations and wound dressings. It’s even used as a glue to repair fine cigars. And of course, you can buy many types of pectin on Amazon. But our primary interest here is agricultural: Pectin has special properties that can be useful in a ruminant diet.
Before we launch into ruminant nutrition, we need some chemistry. Pectin is found in plants as a heteropolysaccharide polymer, which means that it is a large molecule composed of many subunits. Its primary subunit is galacturonic acid and lessor subunits include arabinose, rhamnose, galactose and many others. Let’s translate some terms: saccharide means sugar; poly means many; hetero means not the same. Therefore, the impressive chemical jargon of heteropolysaccharide means that pectin is a large molecule with lots of sugar subunits that are not the same. Which implies that there are many varieties of pectin, depending on the exact proportions and arrangements of those various sugar subunits. And large is large. For perspective, water has a molecular weight of 18, and table sugar (sucrose) has a molecular weight of 342. Pectin molecules have molecular weights that range from 60,000 to 130,000. That’s a lot of subunits.
In nature, pectins are found both inside and outside of plant cell walls. That may sound a bit strange, but pectins indeed perform double duty. Inside the primary cell walls of plants, pectins interact with other large fiber molecules like cellulose, hemicellulose and lignin to create the rigid structure of plant cells. Outside the cell walls, in the microscopic space between cells called the middle lamella, pectins act like a type of glue that binds plant cells together.
So, if pectin is a type of fiber, does a laboratory fiber analysis detect it? Actually, no, it does not. The standard fiber analysis used by modern agricultural laboratories is neutral detergent fiber (NDF) which is very good at identifying the main fiber components of plants: cellulose, hemicellulose and lignin, and also other fiberlike substances such as cutin, silica and the Maillard products (heat-damaged protein). But not pectin. Because of their unique characteristics, pectin molecules dissolve in the neutral detergent and do not show up in the fiber residue but instead are in the solution with starches and sugars. The good news is that some laboratories can use other, sophisticated procedures to test directly for pectin and accurately determine its level.
Now let’s get practical. How digestible is pectin? Well, mammals do not produce the digestive enzymes that can break the chemical bonds in pectin, so in most mammals, pectin molecules flow merrily undigested down the gastrointestinal (GI) tract until they reach the large intestine (colon) where the microbes may ferment it. The effectiveness of this system depends on the animal species: hogs have a large colon, so they can obtain some nutrients from pectin, but chickens do not. And in humans, pectin is considered part of the dietary fiber portion in foods. Which means that it is not digested in the stomach or small intestine, but it can be digested to some extent by the microbes in the large intestine (the microbiome).
In contrast, ruminants such as cattle and sheep can gain a lot of nutrition from pectin. Not because of any pectin-digesting enzymes in the stomach or small intestine, because ruminants don’t have any, but because of microbial fermentation in the rumen. And here’s where the value of pectin truly really shines: Rumen microbes ferment pectin as fast as they ferment starch, meaning that pectin can supply high amounts of energy to the cow.
But pectin fermentation is different than starch. When microbes ferment starch, they produce lactic acid, which can significantly reduce the pH in the rumen. This is important because large amounts of lactic acid can cause acidosis, especially when it builds up quickly when we feed high levels of grains such as corn, wheat or barley. Everyone who feeds grain knows about the risks of acute acidosis. But even smaller amounts of grain have some acidotic effects. Reducing the rumen pH can cause subacute acidosis, which is not fatal but still has profound effects on feed digestibility. If the rumen pH drops from a comfortable 6.5 to below 6.0, this can reduce the population of fiber-digesting bacteria which reduces fiber digestibility and often feed intake. In nutrition courses, we call this the associative effect.
But pectin is different. Its fermentation in the rumen does not cause the associative effect. When the rumen microbes ferment pectin, they follow the path of fiber fermentation, not starch fermentation. The microbes ferment those galacturonic acid subunits in pectin like they ferment cellulose and other plant fibers. Lactic acid is not produced, and the rumen pH is not lowered. No acute acidosis. no subacute acidosis, no associative effect. The sun shines, the birds sing, and we all win the lottery.
What does this mean for practical on-farm nutrition? We certainly can’t run to Amazon every week and buy small packages of pectin, not for 300 cows or even 30 cows. But we can formulate rations with feedstuffs that contain high levels of pectin. For example, citrus waste and apple pomace are obvious choices because they are the main commercial sources of pectin. But there are two other common feedstuffs that contain high levels of pectin: beet pulp and soybean hulls (commonly known as soy hulls). Especially soy hulls, which have been used extensively in high-producing dairy herds to provide energy and fiber.
High-pectin feeds such as soy hulls can be excellent for many situations: fattening rations, creep feeds, starter diets, mixed rations for dairy animals, even for feeding 300 beef steers. They provide plenty of digestible fiber and a much lower risk of acidosis. Which translates to peace of mind.
Using high-pectin feeds depends on economics, of course, and availability. We do have choices sometimes. And in the right situations, things can really gel.
