Linda F. Benedict, McCormick, Michael E., Moreira, Vinicius R., Williams, Cathleen C.
Vinicius R. Moreira, Laura Zeringue, Cathleen C. Williams, Claudia Leonardi and Michael E. McCormick
The growing demand for food and fuel in the world has spurred widespread concern about the sustainability of agriculture’s intensive use of energy and nutrients. Numerous attempts have been made to establish a universal definition for the term sustainability. A common denominator among those is the recommendation "to use less and recycle more in order to achieve an ideal degree of self-sufficiency." Sustainable nutrient use in animal operations involves maximizing outputs – animal products such as eggs, milk and meat – with the lowest need for inputs such as feeds, fertilizers and manures (Figure 1).
An easy and cost-effective method to improve nutrient balance in animal husbandry is to reduce inputs, so long as yields remain similar. The LSU AgCenter strives to maintain research and extension programs targeting farming sustainability because the result is production efficiency – increased output per input unit – a fundamental requirement for the success of any business.
Nitrogen, phosphorus and potassium are among the most essential nutrients in agriculture. Producing nitrogen fertilizer requires large amounts of fossil fuel, tying nitrogen fertilizer prices to fluctuations in the energy markets. Phosphorus and potassium ores are mined from deposits around the world, but mining and transportation equipment are energy-intensive. Prices also spiked after demand for fertilizers increased during the corn ethanol boom.
Excessive use of fertilizers can accumulate nutrients in the environment, changing ecosystems and even threatening cow health in extreme situations. Numerous minute fertilizer sources trickling into a water body – any stream, river, bayou, pond, lake or coastal waters – can contribute to nutrient imbalances. Nitrogen and phosphorus imbalances stimulate algae growth and can cause fish kills.
Collectively called nonpoint sources, those minute nutrient sources include private sewage treatment systems and stormwater runoff, as well as agricultural lands. Agricultural nutrient sources, including fertilizers and manures, are applied on the land for proper crop and pasture production. Any unused excess, however, may run off or leach into surface water or groundwater. The combination of "leaky" urban and agricultural systems can contribute to nutrient enrichment of waters sometimes miles downstream. One approach to abate nonpoint emissions is to increase understanding of the problem through research and education of the individuals involved.
In the case of dairy farms, lactating cows need to be fed nutrient-dense diets to produce milk, a good source of calcium, potassium, vitamin D and protein in human diets. Forage and byproducts account for the majority of ingredients in dairy animals’ diets. Byproducts commonly used include:
It is important to note that none of these feeds alone can provide proper nutrition to productive animals without exceeding or lacking one or more nutrients. Many feeds have to be mixed in varying proportions and offered in different quantities according to the animal’s requirements to minimize costly and wasteful use of our natural resources.
In past years, LSU AgCenter researchers demonstrated that measuring milk urea nitrogen, a simple analytical procedure performed on milk samples, is an effective method to evaluate the adequacy of protein content in diets of grazing, lactating dairy cows. Protein feeds are among the most expensive components in dairy cows’ diets, thus farmers quickly adopted the new technology. This was confirmed in a 2006 survey of Louisiana dairy producers, which showed that producers were more acutely aware of the protein content than any other nutrient in the feeds offered to their cows.
Since 2004, researchers have been tackling another important aspect of nutrient management: proper phosphorus supplementation to dairy cows in Louisiana. Phosphorus needs for lactating cows are well-defined within a relatively narrow range between 0.30 percent and 0.42 percent of diet dry matter, which amounts to two to four ounces of phosphorus per cow per day. Most of that variation is a consequence of milk yield, which includes 0.01 ounce of phosphorus per pound of milk. per pound of milk.
Research and extension programs at the LSU AgCenter Southeast Research Station in Franklinton are demonstrating management practices to increase phosphorus efficiency in dairy operations. In a recent study with highly productive mature cows giving 97 pounds or 12 gallons of milk per day, phosphorus in the diets was reduced by 20 per percent – from 3.6 to 2.8 ounces per day – within the first 30 days of lactation, and phosphorus in the manure was reduced by 30 percent. It was found that not only could cows on low-phosphorus diets extract dietary phosphorus more efficiently, but excessive phosphorus in the diet may negatively influence calcium utilization.
Finally, the 2006 dairy producer survey indicated that most respondents had little knowledge of the phosphorus content in the diets fed to their animals, likely because of the relatively low cost of phosphorus in the supplements. Although phosphorus supplementation cost is among the highest per unit in a cows’ diet, supplemental phosphorus is measured in ounces. Protein is required by the pounds.
AgCenter researchers estimate that at prices taken on Jan. 28, 2010, every 0.1 ounce of phosphorus overfed daily to a cow represents only $6 annually. A tenth of an ounce may not sound like much, but a dietary reduction of that magnitude across all U.S. cows would mean eliminating 10 tons phosphorus in the environment.
In addition, if current feeding practices were adjusted according to recommended levels shown in Table 1, total savings could amount to some $20 to $50 per cow per year. The AgCenter recommends that forages and concentrates should be tested regularly – at least quarterly – for major nutrients, including minerals, to adjust feeding practices. The LSU AgCenter Agricultural Chemistry Laboratory in Baton Rouge and the Southeast Research Station Forage Quality Laboratory in Franklinton are both well-equipped for those analyses.
Vinicius R. Moreira, Associate Professor, and Laura Zeringue, Research Associate, Southeast Research Station; Cathleen C. Williams, Associate Professor, School of Animal Sciences, LSU AgCenter, Baton Rouge, La.; Claudia Leonardi, Biostatistician, Pennington Biomedical Research Center, Baton Rouge, La.; Michael E. McCormick, Professor and Resident Coordinator, Southeast Research Station, Franklinton, La.
(This article was published in the winter 2010 issue of Louisiana Agriculture.)