Reducing Nitrogen and Phosphorus Excretions from Dairies in Gooding and Jerome Counties, Idaho

Reducing Nitrogen and Phosphorus Excretions from Dairies in Gooding and Jerome Counties, Idaho

Summary

Nine dairies, with a total of 11,500 cows, from South Central Idaho were involved in this project. Nutrient flow data at farm level and feeds, manure, milk, and soil samples were collected and are being analyzed for protein and energy fractions and mineral composition. All work planned for this stage of the project was completed. Average concentration of nitrogen and carbohydrate fractions in the diets examined was within the range recommended for high-producing dairy cows, but varied significantly between dairies. Dietary phosphorus concentration was above current recommendations. Milk urea nitrogen concentrations were also high in some dairies.

Objectives/Performance Targets

The objective for Year 1 of the project was to collect data on the nutritional (nitrogen and phosphorus) status of representative dairies in Gooding/Jerome counties. These case studies will provide the needed database on the current nutritional practices in relation to nutrient balance in an area having a high density of dairy cows.

Accomplishments/Milestones

Nutrient flow information.

The following information (by category) was collected at the monthly visits from each participating dairy. Current inventory was established at the beginning of the study:

1. Feed
a. Purchased – type, date, amount, source
b. Produced on the farm – type, date, amount
c. Sold – type, date, amount, destination

2. Milk shipped
a. Amount
b. Composition
c. Destination

3. Mineral fertilizer use
a. Type (NPK)
b. Date purchased
c. Amount used
d. Field to which was applied

4. Animals
a. Purchased – type and live weight, date, heads, source
b. Sold, culled – type and live weight, date, heads, destination, reasons

5. Seeds
a. Purchased – type, date, amount
b. Sold – type date, amount, destination

6. Bedding
a. Purchased – type, amount, date, source
b. Produced on the farm – type, date, amount
c. Sold – type, date, amount, destination

7. Solid manure
a. Produced on the farm – date, amount
b. Exported off the farm – date, amount, destination
c. Used on the farm – date, amount, field to which was applied, distance

8. Liquid manure
a. Produced on the farm – date, amount
b. Used on the farm – date, amount, field to which was applied, distance

Samples taken from the dairy.

Concentrate feeds were sampled three times during the study. Composite samples were oven dried and are currently being analyzed. Hay bales were sampled with a core sampler (approx. 5 to 7 bales per dairy and sampling). A composite sample was oven dried and is currently being analyzed. Silage samples were taken from several locations in the silo, mixed, and stored on ice. A subsample was preserved frozen and the rest of the silage was oven dried and will be analyzed for chemical composition. Diet (TMR, total mixed ration) samples were taken from six locations, mixed, and kept on ice until processed. Diets for each group of cows (fresh, lactating, dry) was sampled separately. Only freshly prepared TMR were sampled. Part of the sample was oven dried and part was stored frozen. Diets were subjected to a variety of chemical analyses (Tables 1, 3, and 4).

Fecal samples were taken from 15 randomly selected lactating cows fed the same diet. Sample cows were distributed evenly across pens fed the same diets. Fresh fecal samples were obtained from the rectum or from the ground. One composite sample per diet fed was stored frozen. After thawing, fecal samples were oven dried and analyzed for acid-insoluble ash (AIA, used as an internal digestibility marker) and chemical and mineral composition.

Urine samples were taken from 10 randomly selected lactating cows fed the same diet. As with the feces, cows fed different diets were sampled separately. Sample cows were distributed evenly across pens fed the same diets. Urination was stimulated by massaging. Composite samples were analyzed for pH, acidified, and stored frozen. Urine samples are currently being analyzed.

Dry manure samples were taken from several locations from each manure pile after the surface layer was removed. A composite sample was oven dried and will be analyzed for chemical composition. Depending on the manure management system, separator solids samples were taken from different locations. Composite samples were oven dried and will be further analyzed. Lagoon samples were obtained with a sampling device from 6 to 8 different locations and at a depth of approx. 1-2 feet. pH of composite samples was determined and samples were acidified and stored frozen for further analyses.

Bulk milk samples were collected from the milk tank. Samples were preserved and analyzed for milk protein, milk fat, milk urea nitrogen (MUN), lactose, and solid non-fat (SNF) residues (Table 2).

Soil samples. Two fields from each of the participating dairies were selected for monitoring. The fields were selected based on consistency of dairy waste application over the past few years. The fields received either lagoon water via sprinkler irrigation or dry waste via spreader trucks in the fall and spring. Each field was sampled in two areas, each area representing the soil and landscape features of a large portion of the field. Samples were taken over a 0.5 ha area in each location to a depth of 60 cm at 30 cm intervals. The positions of the sampling points were recorded with a GPS and resampled in the fall. Soils are being analyzed for N, P, K, macro- and micronutrients, pH, organic matter, and electrical conductivity using accepted soil sampling methods at a certified soil analysis laboratory.

Results.

At this stage we are reporting chemical composition of the diets and milk composition from the participating dairies. Feces, urine, manure, and soil samples are currently being analyzed, but data were not available to be included in this report.

Across stages of lactation, average crude protein (CP) content of the diets from the participating dairies was 17.8% (Table 1), which is within the range of CP routinely fed to high producing dairy cow, but somewhat above current recommendations (NRC, 2001). Reduction in the efficiency of utilization of dietary nitrogen (N) for milk protein synthesis with increasing CP content of the diet has been well documented (Wu and Satter, 2000; Etter et al., 2003; Broderick, 2003). Thus, despite of the increased milk yield, feeding more CP will inevitably result in greater losses of N with excreta, primarily urine. Crude protein concentration in the diets from some of the dairies was high (max of 20.2%). Another important observation was that in some diets solubility of dietary CP was reaching 50%. Soluble protein is very rapidly degraded in the rumen and contributes significantly to urinary N excretion. Diets were adequate in fiber (NDF and ADF, neutral- and acid-detergent fiber, respectively) and contained starch and total non-fiber carbohydrates (NFC) within the range accepted for high-producing dairy cows. Concentration of phosphorus (P) was on average 0.48%, but some of the diets had P concentration of above 0.60%. Phosphorus concentration in lactating dairy cow diets should not exceed 0.38% in order to minimize the environmental impact of the industry. Total digestible nutrients (TDN), net energy of lactation (NEL), and digestibility of dietary DM, determined experimentally, were within normal ranges. Marker methods are usually a compromise between accuracy and practicality and in this study some of the diets tested had unrealistically low digestibility of DM. In all participating dairies, cows were fed separate diets in the early (fresh or high diets, Table 3) and late (lactating cow diets, Table 4) stages of lactation. We did not observe any significant differences between the two categories; crude and soluble protein, fiber, carbohydrate fractions, and P concentrations were similar. Dry cow diets are not reported here.

Analysis of the milk samples collected during the reporting period is shown in Table 2. Fat and protein content of milk was within the range typically reported for high-producing dairy cows. Milk urea N is an indirect indicator of the efficiency of utilization of dietary N and is used as a tool to monitor protein feeding of dairy cows (Carlsson and Pehrson, 1994; Schepers and Meijer, 1998; Jonker et al., 1999). Milk from some of the dairies had high MUN concentrations most likely indicating overfeeding of ruminally degradable protein.

References:

Carlsson, J. and B. Pehrson. 1994. The influence of the dietary balance between energy and protein on milk urea concentration. Experimental trials assesses by two different protein evaluation systems. Acta Vet. Scand. 35:193-205.

Broderick, G. A. 2003. Effects of varying dietary protein and energy levels on the production of lactating dairy cows. J. Dairy Sci. 86:1370-1381.

Etter, R. P., A. N. Hristov, J. K. Ropp, and K. L. Grandeen. 2003. Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows. J. Dairy Sci. 86 (Suppl. 1):59.

Jonker, J. S., R. A. Kohn and R. E. Erdman. 1999. Milk urea nitrogen target concentrations for lactating dairy cows fed according to National Research Council recommendations. J. Dairy Sci. 82:1261-1273.

NRC. 2001. National Research Council. Nutrient requirements of dairy cattle. Seventh Revised Edition. National Academy Press, Washington, D.C.

Schepers, A. J. and R. G. M. Meijer. 1998. Evaluation of the utilization of dietary nitrogen by dairy cows based on urea concentration in milk. J. Dairy Sci. 81:579-584.

Wu, Z. and L. D. Satter. 2000. Milk production during the complete lactation of dairy cows fed diets containing different amounts of protein. J. Dairy Sci. 83:1042-1051.

Impacts and Contributions/Outcomes

This is a progress report. Impacts/contributions will be discussed in the final report.