The role of carbohydrates in dairy cow nutrition

[0:17]Hi, I'm Jane K, I'm a senior scientist at and this is a feed write video on carbohydrates. Now in this video we will talk about the different types of carbohydrates. What happens when how eats carbohydrates and how carbohydrates impact on cow production and performance. So what is a carbohydrate? All plants contain carbohydrates and these provide the main energy source for the cow. There are two main types of carbohydrates that are found in feed. non- structural carbohydrates which contain sugar and starch and structural carbohydrates which include thecelose andhemise. These carbohydrates are all made up of sugar molecules with the only difference being the chemical bonds that join them together. These can be compared with building Lego with the individual Lego blocks are the simple sugars that make up the carbohydrates. Sugar such as found in molasses is like having a pile of Lego blocks, some sugar molecules pulled apart and ready to be used. Then starch, which is high in cereal grains and vegetable waste is like Lego join together in a simple way. They need to be pulled apart before they can be used. Finally, the structural carbohydrates such ascellose and hemicellose that are found in good quality pasture are like having a more complex structure made from Lego that takes different mechanisms to pull apart before they can be used. Luckily, the bugs in the are capable of breaking apart these complex structures, so the sugar molecules or the blocks can be used by the bugs for energy. So, let's have a look in more detail as to what happens to these carbohydrates when they're eaten by the cow. When a cow eats a food, be it a forage or a concentrate, the carbohydrates in this food are broken down or fermented in the rumen by microbes to form simple sugars. The microbes then use these simple sugars as an energy source and doing so produced waste products. These waste products include gases, heat, and volatile fatty acids. The volatile fatty acids are the most important waste products and that they provide the cow with energy and they effect milk fat and milk protein production. There are three main volatile fatty acids produced when carbohydrates are digested and these are acidic, protic and butyric acids or more often called, protic, protic and butyrate. The proportion of each of these acids depends on the type of carbohydrate the cow is eaten and to a lesser extent the room and environment. If the cow is eating a diet high in forages such as pasture orage, these feeds contain high levels of structural carbohydrates. Now that's acelose andses. The microbes that digest these structural carbohydrates produce a large proportion of acetate. Now acetate is absorbed through the rumen wall, it passes into the liver and ex as a building block for synthesis. to produce either milk fat and the memory gland of a lactating cow or body fat and the post tissue of a cow that is gaining condition. The microbes that digest structural carbohydrates are sensitive to high levels of dietary fat and also an acidic environment or low pH of the rumen. If the cow was to eat a diet that contains high levels of unsaturated fats such as sunflower oil or canola oil or if the rumen pH dropped or became too acidic eating a diet high and sugars and starch, the growth rate of the microbes that digest the structural carbohydrates slow down and the microbes themselves may even be eliminated. Reduction or elimination of these microbes reduces the digestibility of feeds that are high in structural carbohydrates such as pasture and can also reduce the cow's intake and performance. In theory, structural carbohydrates are digested about five times slower than starch. And nearly 100 times slower than. However, the structural carbohydrates, the cellulose and that are found in high quality pastes are digested at a similar rate to starch. On the other hand, if pastes are of poor quality due to poor pastes management or dry conditions, there is a build up of in the pastes. Now, although is not a carbohydrate, it binds with the structural carbohydrates and makes them less accessible and harder for the microbes to Now this is like sticking the Lego blocks together with super glue. If the content is high then some of the structural composites pass through the room and and are in the. So let's move on to look at what happens when it feeds that are high nonstructural composites so that's the sugar and the starch. feed high and sugar include and or feeds at a high starch include cereal such as wheat or maize. The microbes that digest start are different from the ones that digest the structural carbohydrates. They primarily produce propionate as their waste products. Now the propionate that's produced in the rumen makes its way to the liver where most of it is converted to glucose. Now the liver is the sole source of glucose production for the liver of which he has a high demand particularly for milk production. An, a large proportion of the glucose has been produced in the liver is transported to the memory gland where it is used to form lactic, which is the main driver for milk volume. What we also see is that if we increase the amount of glucose produced, we see increased insulin and among its other functions, this results in an increase in the uptake of amino acids into the memory gland and an increase in milk protein production. So a diet high in starch, one that contains cereal grains will result in more milk volume and more milk protein. If high levels of starch are eaten, lactic acid can also be produced. and lactic acid reduce the pH or the acidity of the rumen which as mentioned before is detrimental to the microbes that digest structural carbohydrates. In contrast, the microbes that digest the starch are not sensitive to a low rumen pH. Consequently, feeding the high levels of starch and the diet such as or grain can result in a build up of microbes in the room that continue to lower the room pH and this can eventually result in roomosis. If for some reason some starts is not digested in the room, it passes through to the small intestine with a dairy cow only has a limited capacity for digestion and absorption. Therefore, only a small proportion of any digested starch is absorbed from the small intestine and contributes to the glucose pool in the liver. The remainder, like with undigested structured carbohydrates is excreted in the dung. Finally, the microbes that ferment soluble sugars, a carbohydrate that is high in feed such as, are similar to those that digest starch. However, these feeds are generally digested at a faster rate and cause less problems with increased acidity in the rumen. digestion of sugars results in the production of protate and. We've already discussed. Nowate is a little different. As it is absorbed across the room and wall, it is converted to beta hydroxyate and then moves into the liver. Nowate is a ketone body that can also come from the mobilization of body fat when the creatinine is in a state of negative energy balance. Nowate are used by the creatinine as a source of energy. They are also used for fat acid synthesis in the memory gland and and for muscle growth. So in summary, carbohydrates are fermented in the rumen and they are all broken down into the same simple sugars, but different microbes use these sugars to grow and therefore produce different waste products or different volatile fats. If the cow was to eat feeds that are high and structured carbohydrates such as pasture or soya, then is the primary fat acid that is produced and this results an increased milk fat synthesis. If the feed was high in starch such as maize grain, this results in increase proteinate and subsequently an increase in milk protein and milk volume. feeding high levels of sugar such as in beet will result in an increase in rate production and a subsequent increase in milk fat. diets that are too high and non-structural carbohydrates, so that's your starch and your sugar, all of these feeds are introduced into the diet too quickly, they also acid which can lower pH and result in. So by the end of this video you should be able to name the three different types of carbohydrates, describe what happens to these when the core eats them and how they impact on production.