Cooperative Extension Fact Sheet FS1064 | September 2013
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.
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.
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.
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