[MUSIC] Hello, my name is Alex Hristov, and I'm Professor of Dairy Nutrition at Penn State University. In our previous lectures we covered animal requirements, feeds, and feed processing. It's time now to talk about how we feed dairy cows through the various stages of their lactation. Please also check Dr. Varga's lectures on dairy cow nutrition. Formulating a diet for lactating cows is, as the saying goes, science and art at the same time. A good nutritionist or dairy manager will understand animal requirements, feed composition and particularly forage quality, interactions of feeds in the diet and nutrients in the rumen. The nutritionist will also be aware of animal physiology and health, farm economics, and environmental regulations. This is the science part of feeding dairy cows. The art comes with practical experience and the ability to make sense of the multiple variables in a complex production system such as a dairy farm. So as you see, it is simple. First, I'll briefly explain the life cycle of a dairy cow, and how her nutrient needs change during the lactation from parturition, which is giving birth to a calf, to drying off. The life cycle of a dairy cow starts as a calf, then she's a heifer until giving birth and a cow throughout the rest of her life. Please also check Dr. Varga's lectures on calf and heifer nutrition. In intensive production systems such as the dairy systems in the United States, where Holstein-Friesian or just Holstein breed makes up over 90% of the dairy cattle, heifers are usually bred by artificial insemination at around 15 months of age, when they reach live weight of around 390 kilos or 850 pounds, or about two-thirds of their expected mature body weight. The gestation period in cattle is 280 days which is close to that of humans, and Holstein heifers give birth to their first calf around 24 months of age. These cows are called first lactation or primiparous cows, and their lactation patterns and nutrient needs are different than those of older cows, which are called multiparous. After calving, cows are bred again, usually within 80 days, and conceive on average around 140 days after calving. Ideally cows will give birth to a calf every 12 to 13 months, but in the US target calving interval is around 14 to 15 months. Dairy cows are usually milked for 10 months, which is about 305 days, and then they get a break of 50 to 60 days before calving and starting another lactation cycle. Cows in the US have an average life span of 2.4 to 3 lactations. Cows in larger herds and more intensive production systems tend to have shorter productive lifespans than cows in smaller herds and extensive such as pasture production systems. The feeding program of a dairy cow changes according to her nutrient needs during the various stages of the lactation cycle. Terms that we use to describe these stages include far-off period, which begins when the cows are dried and continues until three weeks before calving. Close-up begins three weeks before calving and ends with parturition. Fresh period begins at calving and continues to two to three weeks after calving. Dr. Varga covered the far-off and close-up stages in her dairy cow nutrition lectures. In this lecture we'll discuss feeding fresh and lactating cows. The period of three weeks before and three weeks after parturition is commonly referred to as transition period. As shown in this figure, milk production sharply increases after parturition, reaches peak lactation between 40, 70 days, and then steadily declines until the cow is dried off. Feed intake, however, decreases sharply before calving and cannot catch up with milk production until 120, 140 days after parturition, and the cow is in a state called negative energy balance. From a nutritional standpoint, this is important because the diet during this period should be formulated to minimize the impact of negative energy balance on milk production, animal health, and reproduction. This negative energy balance is the reason cows lose body weight in early lactation as they use body reserves to fuel milk production, and then compensate the loss in mid and late lactation and the dry period. It is normal that cows lose up to half body condition unit on five unit scale during this period. This chart gives you a good idea of the body condition scoring system used in the US. You can also find it in the supplemental materials for this lecture. Milk composition changes during the lactation, and this should be also considered when formulating diets. Concentration of all milk components is much higher during the first several, four to five, milkings, including the colostrum period, which is one to two milkings. Gradually it decreases to lactation week eight, and then levels off and slightly increases as milk production decreases in late lactation. In most dairies, nutrition and grouping of the lactating herd go hand in hand. There are various recommendations as to how to group cows, which consequently plays a role in how many rations are formulated and fed to the herd. The decision to implement one grouping or feeding strategy versus another comes down to economics, which is cow comfort and milk production versus available facilities and labor. Where facilities allow it, first lactation cows should be separated from the older cows, and usually stay separated throughout most of their first lactation. The older second and greater lactation cows can be grouped based on days in milk, which usually reflects their milk production. For example, a fresh group, up to 20-30 days in milk. A high group or high producing cows, between 20-30 to 100 days in milk. A mid group, 100 to 200 days in milk. And a low group, above 200 days in milk. Probably a more common grouping strategy is to have two lactation groups, high and low producing cows, in addition to a fresh group, which means formulating three diets for the lactating herd. Any grouping in any dairy farm will be composed of cows with different milk production, nutritional needs, and social behavior. Therefore, group feeding is a compromise between meeting the nutrient needs of all cows and the practicality of delivering nutrients in bulk to reduce labor and feed costs. Feeding cows as a group inevitably will lead to overfeeding some cows and underfeeding others. Cows partially compensate for this by varying their feed intake. For example, high-producing cows will eat more of the same ration than low-producing cows. Also nutritionists will use so-called lead-factors to assure that the higher producing cows in a group are not underfed. As an example, instead of formulating for the average milk production in a group, they will formulate a ration that is 15% or more above the average group milk production. So what do we need to formulate a diet for a lactating dairy cow? First we need to have a good handle of the nutrient requirements of the breed of cattle we are working with, their specific body weight, milk production and milk composition, physical activity, for example, walking distance to be milked or fed, weather, and pregnancy status. Requirements will change depending on all of these factors. For example, in addition to volume of milk produced, concentration of fat, lactose and protein in milk will have a large impact on nutrient requirements. The higher these components are, the higher the requirements for net form metabolizable energy and or metabolizable protein would be. Second we need to know, or at least have a pretty good idea of, what the dry matter intake of the cows is or would be. Remember that we may formulate diets various ways. But what matters to the cow is how much of one or another nutrient she consumes. So without an accurate estimate of dry matter intake, we will be off with our prediction of animal response to the diet we have formulated. Note that I am using the term dry matter intake. This is because we formulate diets for dairy cows and other cattle based on the dry matter of the diet. Water is an important nutrient, but it does not provide any energy or protein to lactating animal. Therefore, when the diet contains wet feeds such as silage, we have to calculate the nutritive value of that feed and its inclusion rate on dry matter basis. Having accurate estimates of dry matter intake of the cows in a herd also allows calculating the efficiency of conversion of feed into milk. The formula for this is simple. Amount of milk divided by the amount of dry matter intake. It's also called feed efficiency or milk efficiency. A good benchmark for this is 1.5 and above. This means on average the cows are producing 1.5 pounds or kilograms of milk per pound or kilogram of dry matter intake. Efficiency below 1.5 is indicative of a problem along the production line and should be investigated. Finally, in addition to animal requirements and feed dry matter intake, we need to know the nutrient composition of the individual feeds and the entire diet. Forages should be analyzed regularly, weekly, once a month, or when opening a new silo, for dry matter content and chemical composition at least crude protein, fiber fractions, starch if it's a corn silage, and major minerals. Table values for chemical composition of most concentrate feeds such as corn grain or soybean meal, are used for diet formulation purposes. For most byproducts, for example distiller's grains or bakery by-product meal, nutrient specifications provided by the manufacturer are usually a reliable source of information for chemical composition of these feeds. Bottom line is, without any of these three components, animal requirements, dry matter intake, and feed nutrient composition, we cannot properly formulate diets for lactating cows. Generally, nutritionists strive to meet the energy requirements of the cows first. Energy is directly related to digestibility of the diet, and any poor-quality, low-digestibility feed, these are usually the silages in the diet, can have a dramatic impact on the energy content of the entire ration. Forages, starch from grains, and oils are all sources of energy for the cow. Fiber, starch, and sugars are also energetic sources for the rumen microbes. The diet should exceed the calculated energy needs of the animal. For example, if the requirements for net energy of lactation of an average cow is 40 mega calories per day, it will be appropriate, particularly for feed a group of cows, to formulate a diet that would provide 44 mega calories of net energy per day. As part of this process we balance the energy sources in the diet. For example, our target for neutral detergent fiber should be around 30% of the dietary dry matter or 1.0%, 1.2% of the cow's body weight. Much higher fiber content will decrease energy intake due to rumen fuel limitation, and much lower fiber content will lead to digestive disturbances due to lack of effective fiber to maintain salivation and rumen function. Do you remember what effective fiber is and what are the feed sources of effective fiber? If we have all fiber in the diet coming from soy hulls, for example, this will not be effective fiber. Therefore, we usually target around 75% of the dietary neutral detergent fiber to be from forages. Starch should usually not exceed 25% of dietary dry matter. This number will depend on the type of starch and processing and also quality of the forage in the diet. Please check the feed processing lecture for this information. I usually also pay attention to the non-fiber carbohydrates fraction in the diet. This is a calculated number and usually represents mostly dietary starch, but will also include sugars and oligosaccharides, such as fructans, and soluble fiber, such as pectins and beta-glucans. Recommendations for non-fiber carbohydrates are around 40% of dry matter and should not exceed 45%. Some nutritionists and formulation programs also look at total rumen fermentable carbohydrates, which is a better estimate, when it's accurate, of the energy available to rumen microbes. The last energy component of the diet is fat. Total fat in dairy diets should not exceed 6% to 7% of dietary dry matter. In certain circumstances such as hot weather or early lactation, when total feed intake may be depressed, fat can be cautiously increased to increase the energy density of the diet. With fat from feeds in the diet being 3% to 4% supplemental fat, should be in the range of 3 to 4% maximum. At the upper level of this range, supplemental fat should come from rumen-inert sources, which is fat that is protected from rumen degradation and supplies digestible fatty acids through the small intestine. Here's a summary of common feed energy sources in a dairy diet. Good sources of effective and functional fiber for dairy cow diets are country specific, but for the US include high-quality forages such as alfalfa or grass hay, and grass, corn, or small grain silages. Good sources of rumen-fermentable and soluble fiber are soy, cottonseed, almond hulls, sugar beet, and citrus pulp, and combination feeds such as whole cottonseed. Good sources of starch are cereal grains, with processed corn grain and barley being the most widely used. Good sources of rapidly fermentable energy for the rumen microbes are molasses, sugar beet or cane, almond hulls and various by-products of the bakery or candy industries. A good source of fat that is not going to be too detrimental to the rumen microbes is whole roasted soybeans. We'll continue discussing the specifics of diet formulation in our next lecture. [MUSIC]
