The Effects of Altering the Protein Efficiency of Lactating Dairy Cows on the Whole-farm Nitrogen Efficiency of Dairy Farms: Subcontract 1

The Effects of Altering the Protein Efficiency of Lactating Dairy Cows on the Whole-farm Nitrogen Efficiency of Dairy Farms: Subcontract 1

Summary

Whole-farm nitrogen and phosphorus balances were computed for 41 dairies in Utah and Idaho. Whole-farm nitrogen balance was not related to milk urea nitrogen, but was related to herd nitrogen utilization efficiency as measured by nitrogen in milk and meat per nitrogen in feed. Herd nitrogen utilization efficiency had greater impact than crop selection and N application. Manure storage efficiency had the least effect on whole-farm nitrogen balance. Herd phosphorus utilization efficiency was related positively with herd nitrogen utilization efficiency. On farms that grew any crops, as herd nitrogen utilization efficiency increased, whole-farm nitrogen balance decreased.

Objectives/Performance Targets

1. Verify the accuracy of MUN analysis for predicting nitrogen (N) and the N (protein) metabolism of lactating cows in independent digestion studies.

2. Determine the potential use of MUN analysis and a recently developed computer worksheet for predicting N losses and whole-farm efficiencies on commercial dairies in UT and ID.

3. Disseminate all results to agricultural scientists and consultants as well as dairy producers.

Accomplishments/Milestones

1. Verify the accuracy of MUN analysis for predicting nitrogen (N) and the N (protein) metabolism of lactating cows in independent digestion studies.

See 2000 report

2. Determine the potential use of MUN analysis and a recently developed computer worksheet for predicting N losses and whole-farm efficiencies on commercial dairies in UT and ID.

Note: Due to space constraints, only a few tables/figures can be shown. A complete listing of all data can be found in the M.S. thesis of Rhonda Swain, Utah State University, Logan, 2001.

Dairies (n = 41) were selected from 7 counties in Utah and 6 counties in Idaho that met the criteria of at least 5,000 dairy cows and 500,000 lb manure N applied per year. Whole-farm N and P balance information such as sources coming onto the farm (animals, feed, and fertilizer) and sources leaving the farm (milk, animals, manure, and feed) were collected during face-to-face interviews and entered into the Maryland Nutrient Balancer. Required inputs for the program were: tons of purchased feed and fertilizer, tons of crops grown and sold, number of cows purchased and sold, tons of manure exported and its N and P content, and annual milk weights sold. Production characteristics such as milk protein percent, pounds of milk per cow, whole farm average MUN concentrations, and cow and heifer numbers were also collected.

Of the 41 farms, 23 grew any crops, while 18 purchased all feedstuffs. Farms that grew crops ranged from using a small amount to all of their manure on-farm, while farms that did not grow crops exported all their manure. Close to half of the farms in this study (44%) imported all feed. Milk production ranged from 6554 kg/yr to 13,835 kg/yr with an average of 10,344 kg/yr, well above the year 2000 national average of 8276 kg/yr, and consistent with the average (10,143 kg/yr) for herds in this region. There was a large range in the size of herds involved in the study (57 cows to 1960 cows). Average herd N and P utilization efficiencies (HNUE and HPUE), calculated as N or P in meat and milk per N or P in feed, were 21.3% and 31.7%, respectively.
Average farm MUN was used in the model of Jonker et al. (1998) with modifications by Kauffman and St-Pierre (1999) to calculate lactating cow N efficiency and was significantly correlated when regressed on HNUE as calculated by the Maryland Nutrient Balancer (P < 0.05). However, the model accounted for only 11.9% of the variation in HNUE (Figure 1) and was not a good predictor of herd N utilization. This may be because this model was intended to predict lactating cow N utilization efficiency, while the N utilization calculated by the Maryland Nutrient Balancer represents N brought onto the farm from all animals (lactating and dry cows plus heifers) as well as all animal products leaving the farm (milk and meat). Further research in this area may be warranted in order to allow better prediction of herd N utilization.

Herd P utilization efficiency and herd N utilization efficiency were closely related (Figure 2). The management of N appears to be linked to the management of P. This could be because those who are properly balancing rations for N, or protein, are also balancing for P. It may also be a reflection of feeds high in N typically being high in P (e.g., soybean meal). If more attention was paid to improving the efficiency with which N and P were utilized, ration price may decrease, milk production may increase, and environmental liability would decrease.

Whole farm N balance was evaluated separately for those that grew crops and those that did not because this had a significant affect on farm N balance (P = 0.05). Herd N utilization efficiency showed an inverse curvilinear relationship with farm N balance per kg milk and meat N (Figure 3; only farms with crops shown). In both data sets, herd N utilization accounted for more of the variation in farm N balance than any other single variable, suggesting that altering HNUE was the most efficient means of changing farm N balance per kg milk and meat N. The data exhibits curvilinear patterns, suggesting that the effect of HNUE on farm N balance reaches a point of diminishing returns.

On farms where crops were not grown, almost all manure was exported and those farms showed lower farm N balances. The N and P in the manure do not simply disappear when taken off farm. Caution must be taken not to see this as a “quick fix”.
Multiple regression analysis of whole-farm N balance on farms that grew crops and those farms that did not grow crops are shown in Tables 1 and 2, respectively. The model accounted for 90% of the variation in farm N balance per kg milk and meat N. Herd N utilization efficiency alone explained 48.9% of the variation in farm N balance and crop uptake of available N explained 30.2% of the variation. Manure N storage efficiency had a negligible influence on the model. The model for farms that did not grow crops accounted for 84.1% of the variation in farm N balance per kg milk and meat N. Herd N utilization accounted for 53.7% and manure storage efficiency accounted for 34.8% of the variation in herd N utilization. This study suggests that the most important method to improve whole-farm N balance is improved herd N utilization efficiency (i.e. feed utilization/conversion by the cows). The next most important would be crop selection and N application methods, then manure management.

As a final thought, one of the largest areas of potential discrepancy in this study was the possible inaccuracy of N and P input and output estimates. Examining 41 farms and using averages avoided some of this discrepancy, but will not be possible in developing a comprehensive nutrient management plan (CNMP) for a single farm. Larger farms appeared to keep better records than smaller farms. In addition, sampling techniques may be an issue in developing an accurate CNMP. It is difficult to obtain manure samples from a pen of animals or from a storage facility that are representative of the whole farm. Issues of record keeping must be resolved before accurate evaluation of farm nutrient balances can be accomplished.

3. Disseminate all results to agricultural scientists and consultants as well as dairy producers.

Results are being written for submission to appropriate journals and an Extension Factsheet. A paper will be presented at the Intermountain Nutrition Conference in January 2002.

Dissemination of Findings

See above.

Impacts and Contributions/Outcomes

Potential Benefits or Impacts on Agriculture

There is a need for information on quantifying and reducing environmental nutrient losses from dairy farms. Enhancing protein efficiency offers an opportunity to simultaneously reduce environmental N levels and improve profitability of dairy farms through more efficient rations.

Farmer Adoption and Direct Impact

Farmers have yet to see the completed results from this study. Adoption will depend on if they or their nutritionist understands the potential outcomes.

Reactions from Farmers and Ranchers

Individual farm N and P balances were sent to each participating dairy farm, but I have received no feedback from those balances. It may be that the dairy farmer needs additional interpretation of the results and are afraid to ask. The Extension publication will help in this area.

Producer Involvement

We had 41 dairies in Utah and Idaho who participated in this study. A list of each farm was given in last year’s summary.

Future Recommendations or New Hypotheses

Collaborators: