Dairy cows need a diet that will provide both fiber and energy. This is usually met by using wet forages such as silage and hay.
Most dairy cows are fed a total mixed ration (TMR) that includes forages, byproducts, minerals, and vitamins. Working with a nutritionist is critical to make sure that the cow’s nutrient requirements are met and feed costs are minimized.
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Protein
Dairy cows require high levels of protein in order to build and maintain their body tissues as well as support milk production. For this reason, ensuring adequate protein in the diet is very important. However, protein is not the only factor that influences a cow’s feed intake. Many other factors influence how much a cow will eat, and a dairy producer must keep these in mind to maximize feed utilization, reduce waste of nutrients, and increase milk production.
One of the largest factors influencing feed intake is the type of forage the cows eat. While hays are the most common forage source in the United States, silages have gained popularity over the past 20 years due to their improved nutritional value. Silages are fermented grasses and legumes that can be stored for months to improve nutrition and the ability to be used in harsh winter climates.
Another major factor affecting feed intake is the energy density of the ration. The lower the energy content of the ration, the less the cow will eat. In order to improve energy density, producers often add grain or fat to the ration. However, these additions can lead to metabolic disturbances such as rumen acidosis and low milk and milk fat production.
A final factor influencing feed intake is environmental factors such as temperature and humidity. Heat stress can cause cows to eat less, particularly in the pre-fresh and dry periods. Providing adequate shade over feed bunks, free stalls, and holding pens can help alleviate this problem. Providing enough water sources to prevent one cow in the group from blocking all of them is also important.
Dividing the herd into groups based on milk production or reproductive status is a common strategy for optimizing feed intake. This allows the ratio to be tailored more closely to the nutrient requirements of the group. It also helps reduce wasted nutrients such as nitrogen and phosphorus that are excreted in the manure.
Fat
A dairy cow is a ruminant animal and requires an adequate supply of fat in her diet. A typical ration will contain 3%-4% fat, but as the lactation progresses the cow will need more and more. The supplemental fat should be a rumen-inert source such as prilled soybean, canola, or flax oil.
The fat in the ration is used for energy and to meet the requirement for the essential fatty acids needed for the mammary gland to function. In addition, the fat in a cow’s diet helps to control her body temperature.
In order for the cow to meet her nutrient requirements it is important that she have a social structure that encourages feeding. Cows that are reluctant to eat and have poor feed conversion may be at risk of negative energy balance and poor milk production. A low energy intake can also result in subclinical and clinical diseases.
Feeding groups have been shown to improve cow health and production by promoting feed intake. Typically, the herd is divided into high, medium, and low production groups based on milk yield. It is important that the rations fed to these groups match their daily production. A nutritionist can help formulate these rations to reduce the likelihood of a mismatch between dietary demand and supply.
It is important to limit differences in concentrate dry matter proportions between group feedings to not exceed 10-15% between groups. This will help to avoid over-excretion of nutrients in the rumen and improve the efficiency of a ration. Ideally, cows should be grouped according to their peak milk production and fed a ration designed to meet their daily protein requirements. This is called lead feeding.
Carbohydrate
Dairy cows are ruminants, which means they have an extraordinary capacity to consume and digest plants. They spend about 8 to 14 hours every day lying down and chewing their food into smaller and smaller bits before it is absorbed in the rumen and passed to the small intestine for further digestion.
A dairy cow requires a diet that can provide enough energy to support her milk production and maintain health through stressful periods of time such as pregnancy, calving, and post-partum recovery. Energy is supplied primarily from carbohydrate feed ingredients. The amount of energy a cow eats depends on the type and quality of the carbohydrates she receives and her dietary and environmental conditions.
The energy available from the carbohydrates in a dairy cow’s diet is measured as gross energy (GE) and net energy (NE). GE includes all chemical forms of energy, such as carbohydrates, fat, and protein. NE is the sum of GE, fecal energy, and gaseous energy (energy lost in the expulsion of urea).
Feeding the ration to match the energy needs of different production groups reduces waste from the excretion of unused feed nutrients. This also reduces the amount of nitrogen and phosphorus that is lost in the environment.
Grouping cows by days in milk, stage of lactation, or reproductive status provides a good way to tailor the rations to their needs. It is important to monitor the actual intakes of the cows in each group to ensure that they are receiving the correct nutrient mix.
A nutritionist can help develop the best strategy for group feeding, formulate a TMR, and evaluate the performance of each group of cows. It is also important to consider the quality of the feed ingredients used in a ration, as these can have a significant impact on the nutritional value of the resulting ration.
Fiber
Dairy cows require a high-quality diet that can deliver energy and protein relative to their intake capacity. Providing these nutrients is challenging because of dairy cows’ physiological needs (rumen health, metabolic efficiency) and feeding behavior (eating rate, feed conversion).
Forage quality and availability are primary determinants of dietary protein production. If forages are short of plant protein, supplemental protein is required to achieve desired milk protein levels. Optimal rations will contain a mix of protein from grains, legumes, and rumen undegraded protein. The inclusion of rumen-stable fats is another strategy to improve the nutrient density of a dairy cow’s diet.
Supplemental fat feeding should be done according to certain guidelines, as not all cows respond equally to added fat. Adding fat to the diet usually results in a stable or slightly higher milk fat percentage with a minimal increase in milk protein test and increased milk solids-not-fat.
Adding supplemental amino acids can help meet the limiting amino acids methionine and lysine, particularly in early lactation. Methionine and lysine are required for rumen protein synthesis and must be supplied through the diet, or a limiting nutrient will occur. Ideally, a dairy ration should have a methionine-to-lysine ratio in the range of 3:1 to 4:1 for optimal performance.
The total mixed ration (TMR) method of feeding dairy cows is the most widely used practice on dairy farms worldwide, and it provides a means for delivering a highly digestible diet to high-producing dairy cattle that closely matches their nutritional requirements. However, it is important to understand the physical or roughage characteristics of a TMR and its impact on rumen function, digestion, and cow performance. Roughage particle size should be as long as possible to maximize rumen function and digestion.
Minerals
Dairy cows require a variety of minerals to be healthy and maintain high milk production. Trace minerals, such as cobalt, copper, iron, magnesium, manganese, selenium, and zinc, are required in extremely small quantities – usually micrograms or nanograms per day. These trace minerals are critical components of metalloenzymes that influence metabolic reactions and immune function, among other things. Minerals like sulfur are also important for protein synthesis and carbohydrate and lipid metabolism in ruminants.
Energy is supplied to dairy cow’s feed primarily by the digestible carbohydrates in their diet. The amount of energy that is digested and absorbed by the cows depends on the type of feed and rumen conditions. The amount of energy provided by the dairy diet is measured as gross energy (GE), which includes energy from carbohydrates, fats, and fiber. The GE is converted to metabolizable energy by the cows to produce milk and maintain body heat.
Forage is the primary source of energy for dairy cows and represents about half of their diets. The majority of forages are silages (36%) and hays (12%) made from grasses and legumes. Silages are fermented to preserve nutrients and improve their digestibility.
Most dairy farms feed a total mixed ration (TMR) consisting of a mixture of forage, grains, and byproducts from the human food supply chain, such as almond hulls, cottonseeds, or soybean meal. The TMR is formulated to provide the dairy cow with the desired nutrient balance in order to meet her nutrient requirement and maximize her performance. It is common practice to group cows by their milk production level and stage of lactation in a feeding system so that a TMR can be tailored more closely to the cow’s nutrient requirements, reducing waste and excretion of unused nutrients.