Nitrogen and phosphorus 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, especially those on small farms, reduce nitrogen and phosphorus losses by monitoring and/or changing feeding and management practices. This can result in less waste and ultimately a healthier, cleaner, and safer environment. Wasted feed and wasted nutrients also represent wasted money for the farm.
Nutrient inputs on a farm consist of feed, animals, irrigation water, fertilizer, legume nitrogen, etc. Outputs are meat, milk, animals, crops, and manure. When inputs exceed outputs, losses will be present in feed or barnyard waste, in manure, and in lot runoff, etc. These losses may result in excess nutrient storage in the soil. Nutrients may leach through the soil (nitrate) into ground water or run off the soil surface (phosphorus and nitrogen) and directly transported 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 will require 29.2 tons of nitrogen and 2.6 tons of phosphorus per year. Outputs (meat, milk, fiber, etc.) will be 6.9 tons of nitrogen and .8 tons of phosphorus, resulting in 22.3 tons of nitrogen and 1.8 tons of phosphorus for disposal, usually through spreading on available land. Similar calculations can be made for all livestock species. See "Whole Farm Nutrient Balance"...
If nutrients are overfed, or if feeding is mismanaged on an individual farm, this will result in more nutrients to manage in manure or as spoiled feed. While these nutrients can be applied to crop or hay ground to raise feed, it is important to try and keep this recycling loop as balanced as possible to avoid build-up of excess nutrients. Proper animal feeding and management practices can ensure that feed nutrients are not wasted, not overfed, and feed efficiency will be optimized on the farm.
Feeding a balanced diet, avoiding overfeeding, and providing abundant supplies of cool, clean, and pure 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. (See Figure below.)
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. It is impossible for all nutrients to be in a perfect balance in commercial or practical diets, but we want 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 to 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 animals’ requirement for water will increase. A lactating dairy cow requires on the 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; an adult sheep between 1 ½ 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.
If we want our animals to reach maximum levels of production, then they will only have optimum feed intake if they receive adequate amounts water. 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 is not related to runoff or contamination on the farm in the same way that overfeeding or imbalanced 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.
Check out the list of helpful feed management tips for practical ways to manage feed and nutrients. Some of the topics on the page include:
Feeding animals is both an art and a science. It is a science influenced by years of research and it 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.
Authors: Michael L. Westendorf and Carey A. Williams, Extension Specialists in Animal Sciences, Rutgers, The State University of New Jersey. This article was originally published as Rutgers Cooperative Extension Fact Sheet FS 1064. Updated November 25, 2008.