Nitrogen (N) and phosphorus (P) from agriculture sources can affect water quality. These nutrients are required for plant and animal growth, but too much in agricultural runoff can result in environmental and health concerns. This fact sheet provides some guidelines to help livestock producers reduce N and P losses by monitoring and/or changing feeding and management practices. This can result in less waste and ultimately a healthier, cleaner and safer environment.
Farm Nutrient Balance
Nutrient inputs on a farm consist of feed, animals, bedding, fertilizer, and legume N. Outputs are meat, milk, animals, crops, and manure. When inputs exceed plant and animal requirements for N and P, losses will be present in feed or barnyard waste, in manure, and in lot runoff, etc. These losses may result in excess nutrients stored in the soil. Nutrients may leach through the soil into groundwater or lost as soil surface runoff that may be a direct risk to surface waters. Each farm should be seen as a complete system or cycle with inputs, outputs, storage, losses and recycling all taking place. To illustrate, a 120-cow dairy farm requires 29.2 tons of N and 2.6 tons of P per year for maintenance, production, reproduction, lactation and work. Outputs (meat, milk, eggs, wool, etc.) will be 6.9 tons of N and .8 tons of P, resulting in 22.3 tons of N and 1.8 tons of P for disposal, usually through spreading on available land or off-farm disposal. Similar calculations can be made for all livestock species. If nutrients are overfed, or if feeding is mismanaged , this will result in more nutrients for disposal.
To manage manure on the farm it is important to maintain this recycling loop. Proper animal feeding and management practices can ensure that feed nutrients are not wasted, not overfed, and feed efficiency is optimized on the farm.
Feeding a balanced diet, avoiding overfeeding, and providing abundant supplies of cool and clean water will help to optimize feed and nutrient use on an animal farm.
One way to understand nutrient requirements is to imagine a stave barrel. Only when all staves making up the barrel are the same length will water stay in the barrel. If all staves are 3 feet long, all the water will stay in the barrel. However, if one stave is a foot and a half long, then all the water will run out of the barrel to the level of a foot and a half. That is exactly what is happening with a balanced diet. If all nutrients are in a perfect balance, then there will be no excess and no wastage. (See Figure 1 below).
It is impossible for all nutrients to be in a perfect balance in commercial or practical diets, but one wants to come close to meeting an animal's nutrient requirements. If the diet is balanced except for one underfed nutrient, then the entire production of the animal will be limited to the level of that "limiting nutrient" and all other nutrients will be wasted.
Overfeeding can be harmful to animals and to the environment. Animals that become overconditioned or obese may be unproductive and at greater risk of health problems. Excess feed is often wasted and may remain in the feeding area, become contaminated, and end up in the manure pile.
Water is the most abundant, cheapest, and least understood of all nutrients required for livestock production. Water is of concern whenever it is in short supply or contamination is suspected. If subfreezing temperatures turn water into a frozen nutrient, it will mean trouble for domestic livestock. Distress is often brought on by cold wet winter weather requiring an animal's digestive system and metabolic processes to function at peak efficiency to convert feedstuffs to energy so that they can remain warm, healthy, and productive. Conversely, in hot summer weather, water is essential for the animal as well. It serves to cool the animal and works as a solvent or buffer for chemical reactions in the body. When the weather is hot in the summer, an animal's requirement for water increases. A lactating dairy cow requires on average between 15 and 35 gallons of water per day; non-lactating dairy and beef cows require about 15 gallons per day; an adult horse will consume up to 15 gallons per day, which will increase 2 to 3 times when exercising; adult sheep between 1½ and 3 gallons a day; adult swine from 3 to 5 gallons per day; and adult hens about a pint. A quick rule of thumb is that for every 2 pounds of dry feed intake, an animal should receive one gallon of water. This will vary with stress, weather conditions, heat, cold, disease, productive state, work, exercise, etc., as well as the water and salt content of the feed.
Often the first sign that water consumption is inadequate is when animals stop eating. Water is essential to maintain adequate feed consumption. How does this affect nutrient management? If one wants animals to reach maximum levels of production then they will only have optimum feed intake if receiving adequate amounts of water. The level of salt in the water or the diet can influence water requirements as can the presence of heavy metals, nitrates, microbes, and algae.
Water intake is not related to runoff or contamination on the farm in the same way that overfeeding or unbalanced diets are, but water influences the ability of animals to use feed. If water is inadequate or contaminated, then animals will use diets less efficiently, eat less, be less productive, and may excrete more nutrients in waste.
Tips for Feeding
- Nitrogen management. Diets should be managed to reduce N losses. Protein is the chief N source in the diet and N can be a risk to water and environmental quality when mismanaged. If a growing pig requires 22% protein in the diet and we feed 25% protein then the excess 3% (containing N) is going to be lost. Some of it is going to be lost in the feces and some that is absorbed is going to be lost as urea in the urine. Conversely, if a pig requires 22% protein, and we only feed 18% protein then that animal's production will be limited to the 18% level. In this case other nutrients in the diet will be in excess.
Nitrogen feeding strategies are different for all livestock species. For example, ruminants (cow, sheep goat, etc.) have a requirement for proteins that are quickly degraded in the rumen and also a requirement for proteins less quickly degraded or undegradable in the rumen. If too much undegradable protein is fed, then some of that excess will probably be excreted in the feces. On the other hand, if too much degradable protein is fed, there will be too much absorption of N into the blood supply and it will be lost in the urine as urea. Most research has shown that lactating dairy cows require about 32 to 38% undegradable protein in the diet, with the remainder being made up as degradable protein.
With single stomached animals, like chickens, horses, and pigs, individual amino acids are the basis of diet protein formulation. (Protein is composed of individual nitrogen-containing amino acids). Since a ruminant has the capacity to produce essential amino acids in the rumen, there is less focus on amino acid nutrition. But in the case of pigs, horses, and chickens each individual amino acid is important. Lysine is usually the first limiting amino acid when feeding pigs and horses, and methionine is usually first limiting with chickens. Commonly used feeds are limiting in these amino acids and must be supplemented through balancing with other feeds or by adding individual amino acids to the diet.
- Phosphorus management. Phosphorus is required in the diet of animals, but if overfed or wasted, can contaminate the environment and water supplies. Cereal grains fed to livestock contain phytate-bound P. Phytate-bound phosphorous is available when fed to ruminant animals such as cows, sheep and goats, but it is unavailable and cannot be digested by single stomached animals, such as pigs and chickens. Phytate consists of a carbon ring structure with balanced phosphate groups surrounding the ring. Corn and other cereal grains such as wheat, barley, or oats, contain phytate-bound phosphorous unavailable to pigs, chickens and other single stomached animals. Phosphorous from other sources is supplemented to meet the P needs of the animal. The extra phytate-bound P will be unavailable and excreted in the manure. As for horses, since they are hind gut fermenters, they are able to process the P much like ruminant animals.
It is possible to feed a lower percentage of cereal grains in the diet. However, cereal grains commonly make up the major percentage of the diet for pigs and chickens and there are few economic alternatives. Plant breeders may be able to breed feed grains lower in phytate content and higher in available phosphorus. Another option is the use of an enzyme called phytase that can be included with the diet. Phytase breaks down phytate and releases available phosphorus. Mixing phytase (commercially available) in the diet reduces the phosphorus required for the animal. Another factor affecting phosphorus availability is the presence of other nutrients in the diet. Overfeeding calcium can limit the availability of phosphorus. Calcium and other nutrients should be fed in balance so as not to disrupt the availability of phosphorus.
Horses are a bit unique; they require calcium and phosphorus to be in a specific ratio in the diet. Young growing horses as well as lactating mares should receive a Ca:P ratio of 2:1 although higher levels are acceptable especially if alfalfa is a part of the diet; mature horses not reproducing can get by with a 1:1 ratio. Calcium should never be fed at a level lower than phosphorus because phosphorus will tend to interfere with calcium absorption into bone. Horses at maintenance require 0.17 % phosphorus in the diet and 0.24 % Ca. The highest levels of phosphorus are needed in reproducing mares (0.34 %). Typical horse diets approach 2 to 3 times the required level of phosphorus, which can be detrimental to the environment. This high phosphorus level is partially due to the estimated Ca:P ratio in alfalfa hay being 6:1. Many horse owners try to counter act this by adding more phosphorus to the diets. Many equine supplements already contain more phosphorus than is necessary.
There are also phosphorus concerns for ruminant animals such as cows, sheep and goats. Ruminant animals have a phytate enzyme produced naturally within the rumen that breaks down phytate-bound phosphorus and makes it available to the animal. According to the National Research Council, a lactating dairy cow requires between .35 and .40% phosphorus in the diet. Previous dairy feeding practices included as high as .55 or .60% phosphorus in the diet. This would mean an excess of 25 to 30 pounds fed to a cow in a normal lactation. If you multiply this over a dairy herd with 100 cows, then nearly 3,000 pounds extra phosphorous would be fed over the course of a year. Some dairy farmers think that phosphorus is a mineral required for proper reproductive function. While phosphorous is indeed important for normal bodily functions and is important for reproduction, as are other nutrients, there is no special link between phosphorus and reproduction in a cow. Most dairy farmers have already reduced phosphorus in their diets to levels given by the National Research Council.
- Use feed ingredients high in nutrient availability. The availability of individual nutrients can vary from feedstuff to feedstuff; for example phytate-bound phosphorus in cereal grains. It is important for producers to choose feedstuffs that have nutrients high in bioavaility. This means that nutrients present in feedstuffs are readily available and utilized by the animal. Generally, most commercially available feeds that are not contaminated (molds for example) in any way will be acceptable feed sources.
- Cut feed wastage. It is common for animals to spill or waste feed. For example, pigs may waste up to as high as 20 % of their diet while eating. This wasted feed is often wet, covered with saliva, and will spoil and rot if left, and animals will not consume it. Silage, fed to dairy and beef cows, left in the feed bunk and not consumed will quickly spoil and not be eaten. Bunks and feeders should be designed to reduce wasted feed. They should be cleaned on a regular basis so spoiled or rotten feed can be removed. It is often common for animals to be fed on the ground; there is no greater source of waste than feeding animals on the ground. Although this might be acceptable with beef cows or sheep on the open range, or even horses, it is not acceptable to feed animals on the ground near a stream. This sort of waste from organic matter or feed also contributes to the creation of mud in pastures and paddocks.
- Monitor health and disease. Sick animals are not productive animals but will continue to consume feed since they have a requirement for body maintenance. They will continue to excrete nutrients in their manure. All animals should be on a regular health and herd management program. They should be vaccinated for disease regularly and monitored for special diseases. All domestic livestock animals can be affected by parasites. Parasites will infest the intestines and can result in substantial decreases in performance. Whenever this happens, the efficiency of nutrient utilization is going to decline and influence nutrient excretion. All animals should be on a regular deworming and parasite control schedule.
Toxins in the feed or water may also influence animal production. For example, during a drought year forage quality will often decline, and toxins such as nitrates may be taken up from the soil by plants and influence animal production. Plant growth stress can also result in the formation of mycotoxins in the feed; this can occur in both feed grains and forages. These toxins can result in decreased production as well as sickness and death and may be a risk to human health. Whenever toxins are believed to be a problem, it is important to test feed and water supplies to ensure the adequate consumption of un-contaminated feeds and water.
- Monitor feed and forage quality. Every effort should be made to use feeds of high quality. For ruminants to reach optimum levels of production, it is essential that forages be of the best quality possible. Those too high in fiber or rained on during production or that spoil in the silo, will result in lower levels of production, will be more costly to the producer, and may result in greater levels of nutrient loss. Every extra day beyond the optimum harvest date for hay in the summer will results in a reduction in forage quality and greater costs to the producer. This is an important point to remember; harvesting forage at the optimum time will improve quality, result in greater profitability for the producer, and less waste of feed and nutrients.
- Feed variability. Every load of feed that comes out of the field during harvest or delivered by the feed company is different from the previous load. Every bale of hay in the summer is different from the previous bale. Every scoop of grain given to a horse or livestock animal is different from the previous container of grain. It is essential that producers get a handle on the variability of their feed and ensure that to the best of their knowledge and ability they are able to balance diets for the nutrients that are in the feeds they are using. There are feed and forage labs in the region and feed samples can be sent to these labs to determine nutrient content. In this way diets can be formulated based on the nutrient content of each individual component. It is possible to use published values when nothing else is available. However, these are only averages of many samples and may not reflect actual conditions. (See Rutgers Fact Sheet – FS935)
- Feed processing. Processing feed is helpful if animals are to digest and absorb nutrients. In recent years, the use of corn silage kernel processors has increased on dairy farms. Kernel processors will further process each kernel of grain and make the nutrients in the kernel more available to each individual animal. This has been shown to result in a several percent increase in production in animals fed these diets. Feed processing includes grinding, flaking, steam rolling and all processes that improve the availability of nutrients. For example, sorghum grain or milo is unavailable to ruminant animals and horses without some level of processing, such as grinding or steam flaking. It can be utilized by chickens that have the advantage of the crop and gizzard in their digestive system. If there is any down side to feed processing, it would be over-processing or over-mixing. Mixing feeds, particularly forage, for too long of a period of time can break nutrients down more than is required for optimum utilization and health of the animal. Processed feeds are also more expensive than if left unprocessed, and might not always be necessary (e.g. oats).
- Use of by-products feeds. By-product feeds are often used in feeding animals. These are by-products of certain other feed and commodity industries, such as the production of distilled spirits and beer, wheat processing, corn milling, etc. Products from the production of spirits such as brewers grains and/or distillers grains can make excellent animal feedstuffs. There are also by-products from the wheat milling industry, such as wheat bran, middlings, reddog and shorts; and there are by-products from wet corn milling such us high fructose corn syrup or other corn processing byproducts including corn gluten feeds and meals. In addition, there are products such as citrus pulp, beet pulp, and whole cottonseed. All these can make excellent feeds, but have the disadvantage that their nutrient content is often variable; these feeds should be sampled regularly so estimates of nutrient content can be used in formulating diets.
- Additives. Additives, supplements, hormones and antibiotics can help to improve animal performance. These should be used as prescribed on the label, or under the care of a veterinarian. Examples of additives are products like monensin or bovatec, which affect fermentation in the bovine rumen and improve performance and feed efficiency; hormones such as anabolic implants and steroids that improve production performance and growth rate, and antibiotics, which when used properly in the diet, can result in improved feed efficiencies and health. Products that improve nutrient efficiency will also reduce excretion relative to production.
Feeding animals is both an art and a science. It is a science influenced by years of research and is an art developed by centuries of practical experience. Healthy animals fed balanced diets and provided with abundant supplies of fresh water will be the most productive. These animals will be the most profitable to the farmer and the most efficient users of nutrients.
- National Research Council. 1989, 1994, 1996, 1998, 2001, 2007. Nutrient Requirements of Horses, Poultry, Beef,Swine, and Dairy. National Academy Press, Washington, DC.
- Ralston, S. L. 1993. Analysis of Feeds and Forages for Horses. Rutgers Cooperative Extension. NJAES. Fact Sheet FS714.
- Singer, J. W. and D. L. Lee. 1999. Feed and Forage Testing Labs. Rutgers Cooperative Extension. NJAES. Fact Sheet FS935.
- Williams, C. A. 2004. The Basics of Equine Nutrition. Rutgers Cooperative Extension. NJAES. Fact Sheet FS038.
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