Vinicius R. Moreira, Brian D. LeBlanc and Cathleen C. Williams

Current estimates suggest that by 2050 the world population could rise by 2.5 billion people from the current 7.5 billion, and only a quarter of the population will live in rural areas. Synthetic nitrogen fertilizer and improved crop varieties are examples of technologies that have helped increase food availability, allowing the human population to flourish during the past century. Agricultural land availability is decreasing because of urbanization and rising land values, while demand will rise because of population size and increased wealth, especially in less-developed countries.

Recent studies question agriculture’s ability to keep pace with population growth. At the same time, agriculture profitability has been decreasing in recent decades because of high production costs and low product prices. Furthermore, society is increasingly demanding that producers minimize the use of plant nutrients that may escape the farmland and harm vulnerable environments. Thus, producers are under ever-growing pressure to produce more but with fewer resources.

In the case of nutrient pollution from excess nitrogen and phosphorus, several approaches may address the issue, including improved waste treatment systems, practices such as using cover crops that maximize nutrient cycling within the farm, using filter strips to prevent excess nutrients from leaving the farm, and limiting moving nutrients to the farm in the form of fertilizer and animal feed, which have the added benefit of reducing operating costs. A number of studies at the LSU AgCenter have addressed opportunities to improve profit margins while minimizing the potential for environmental pollution from animal production.

Two of those studies evaluated reducing protein feed supplementation by 16 percent and 10 percent. Protein, defined in animal nutrition as the nitrogen content in feeds, was reduced in the cows’ rations by replacing soybean meal with dry distillers grains and solubles. Rations were supplemented with rumen-protected amino acids lysine and methionine according to amino acid requirements for late-lactation cows. The studies differed in forage source, using corn silage in Study 1 and ryegrass silage in Study 2. Feed and water intake, milk yield and composition, and animal body weight and condition scores were recorded. Cow performance did not differ statistically, indicating dietary protein can be reduced from current recommendations so long as adequate levels of lysine and methionine are supplied in the rations. More importantly, milk urea nitrogen content, an indicator of dietary protein utilization in dairy cows, decreased by 42 percent in Study 1 and 35 percent in Study 2 (Figure 1). It is generally recommended that milk urea nitrogen levels be kept below 12 milligrams per deciliter. The results suggest adequately balancing diets for amino acid content could reduce protein waste and potentially reduce feeding costs, a win-win situation for dairy producers.

In another study, AgCenter researchers evaluated the performance of dairy cows fed diets containing no supplemental phosphorus for the first two lactations. Two groups of 14 cows each were fed diets containing phosphorus supplemented in the diet dry matter as monosodium phosphate or not (0.39 percent phosphorus versus 0.35 percent phosphorus in lactation 1 and 0.42 percent phosphorus versus 0.36 percent phosphorus in lactation 2). Cow performance did not differ statistically between the two treatments with cows producing more than 80 pounds per day on average for the first 110 days in milk in both lactations. Excess phosphorus in dairy rations has been shown to be lost in manure rather than absorbed by the animals. If producers avoid purchasing mineral phosphorus supplements, that amounts to cost-savings and reduced potential for phosphorus runoff from soils receiving manure.

AgCenter researchers also evaluated the effect of feeding biochar, a form of charcoal, at incremental levels — 0 to 4 percent biochar in five increments in Study 1 and 0 to 2 percent biochar in nine increments in Study 2 — on the performance and nutrient excretion of broiler chicks up to 18 days of age. The manure of chicks fed incremental levels of biochar tended to have lower concentrations of phosphorus at the higher levels of biochar in the feed in Study 1, while a similar response was statistically significant in Study 2. However, chick weight gain decreased as biochar content increased during Study 1, while body weight change was not significant in Study 2. Although biochar supplementation may potentially decrease phosphorus concentration in broiler chick manure, it needs to be further investigated to ascertain its effect on bird performance, on nutrient excretion and on manure-amended soils.

Vinicius R. Moreira is an associate professor in the School of Animal Sciences; Brian D. LeBlanc has the Roy and Karen Pickren Professorship in the School of Plant, Environmental and Soils Sciences and is a specialist with Louisiana Sea Grant at LSU; and Cathleen C. Williams is the Gerald A. Simmons Professor of Dairy Science in the School of Animal Sciences.

(This article appears in the fall 2017 issue of Louisiana Agriculture.)

Figure 1. Small ration adjustments can help minimize nutrient losses from animal agriculture. The graph shows the effect of precision feeding dairy cows dietary crude protein (CP) on milk production represented as milk urea nitrogen (MUN) in milligrams per deciliter.