Journal of the NACAA
ISSN 2158-9429
Volume 10, Issue 2 - December, 2017


An Assessment of Whole Farm Nutrient Balance on Mid-Atlantic Horse Farms

Swinker, A. , Extension Horse Specialist, Pennsylvania State University
Kniffen, D. M., Extension Beef Cattle Specialist, Pennsylvania State University
Harper, M. T., Research Assistant, Pennsylvania State University


Surveys of 23 horse farms in the Chesapeake Bay Watershed were conducted to assess their potential impact on water quality. Whole farm nitrogen (N) and phosphorus (P) balances were estimated for 13 of the surveyed farms. The project covered 2010-15, measured sediment and nutrient losses on high density horse operations located in the Chesapeake Bay Watershed; and recorded environmentally sound farm management practices. Fresh and composted manure, hay, feeds, and soils were sampled on all 23 farms. Rations were evaluated on 21 of the farms for crude protein and P content. One study looked at nitrogen and phosphorus inputs on 13 horse farms to determine the risk of horse farms for non-point source pollution. Amounts of imported fertilizer, hay, concentrate, and bedding were obtained from farm managers for an entire year. Samples of hay, concentrate, and bedding were taken from each farm and analyzed for N and P. The majority of the horses on the farms were non-breeding horses, for which the only managed output was manure. Four of the farms did not export any manure, 3 exported a small portion of their collected manure and 6 exported all their collected manure. Whole farm balance inputs averaged 53 kg N per 1000 lbs of animal (animal unit or AU) and 13 kg P/AU. Whole farm balances ranged from 100% retention of imported nutrients where no products were exported to a negative balance where all collected manure was exported. Average N and P whole farm balances were 73% and 51% retention of inputs, respectively. With limited export of nutrients from horse farms in foals or manure, more manure must be exported and/or nutrient imports must be decreased to approach nutrient balance and decrease the risk of excess nutrients. The 23 surveyed operations were used to develop a baseline for total nutrient balances and levels for the Pennsylvania horse industry.


In Pennsylvania, there has been an increased emphasis on farm and nutrient management practices on equine operations due to expansion of environmental regulations. Of the 31,000 operations which house horses in Pennsylvania, 23,250 are non-commercial operations and over 75 percent are on limited acreage, requiring intensive management.  Managers of equine operations frequently do not have agricultural backgrounds and need assistance with farm management plans. Pennsylvania is faced with other challenges as approximately 2/3 of horse farms (NASS, 2015) are located in the Chesapeake Bay watershed, where federal cleanup requirements and initiatives are placing demands upon Pennsylvania to meet the nutrient and sediment discharge reduction requirements from agriculture and other sources.

Proper management of equine operations requires a series of complementing Best Management Practices (BMPs) that implement strategies to preserve pasture vegetative cover, to balance nutrient production with nutrient utilization, to properly manage excess manure nutrients, and to manage equine operations for minimal release of sediment.

These field studies were developed to identify needed BMPs for the equine industry and help farm mangers understand, select, and implement sustainable agronomic farm management practices. The projects consisted of three components: Documentation of existing practices and conditions on equine operations, increase knowledge and skills, and on-farm implementation of BMPs. These surveys, covering 2010-2015, measured sediment and nutrient losses for high density horse operations; and recorded environmentally sound farm management practices. Whole farm nitrogen (N) and phosphorus (P) balances estimated on these farms was a major goal for the project. 

What is Whole Farm Balance? 

Whole Farm Nutrient Balance management is required for the reduction of nitrogen loss in agricultural and animal production. Reduced loss from one farm component is easily negated in another if all components are not equally well managed. The challenge is to manage the animals, crops, and other farm components to use available manure N efficiently, and thus reduce the potential loss to the environment (Rotz, 2004). Nutrient accumulation occurs when nutrient inputs exceed nutrient outputs (Van Doorn et al., 2004). Whole farm nutrient balances of inputs and outputs can be used to assess the risk of non-point source pollution and identify pollution reduction strategies (Koelsch and Lesoing, 1999). Nutrient balances can be conducted on several levels including regional, whole farm, and field scales (Lanyon and Beegle, 1989).

Whole farm or “farm gate” nutrient balances compare those substances containing the nutrients of concern, which go in and come out of the farm gate (Brouwer, 1998). Products typically going onto a farm through the gate include purchased hay and grain or concentrates, mineral fertilizer, manure, bedding, and live animals (Brouwer, 1998). Products typically leaving a farm through the gate include crops, eggs, milk, meat, fiber, live animals, and manure (Brouwer, 1998).

Using Feed Ration Evaluations to Balance Rations
Animal excretion of manure N can be reduced by improving the balance of protein or amino acids fed to meet the requirements by individual animals or animal groups or by improving production efficiency (Rotz, 2004). Generally, these management options have applied to dairy, beef, swine, and poultry production. However, all animal species should be able to incorporate BMPs that can help to reduce N excretion. A major deterrent in reaching a nearly perfect balance is feed cost and profit (Rotz, 2004). However, in the horse industry the deterrent appears to be management traditions, connivance, and a lack of independence. However, in the equine industry feed/supplements cost is not an issue. 

In a Pennsylvania SARE Project Report (Swinker, 2013), farm managers reported, it was very difficult for horse owners to balance horse's rations. Most farms use a commercially mixed feed concentrate that could not be adjusted. Each individual horse was fed a specific diet arranged for that specific horse. One farm had 70 horses, and reported that all horses were on their own specific individual diet. Most of the farms reported feeding hay by different weekly truck loads and they did not produce their own hay on their farms. All the hay was imported from off the farms, often by different suppliers. This project showed equine ration’s protein and phosphorus levels above the NRC (2007) requirements. In most cases, farm managers are unable to make major feed ration adjustments due to these reasons.

USDA Natural Resources Conservation Service (NRCS) in some states in the Chesapeake Bay area are offering animal operations management practice through their Environmental Quality Incentives Program (EQIP) to help farmers improve feed management (Ludwig et al., 2013). By helping farmers formulate their rations more accurately to meet their herd’s production requirements, these partners (agencies and Universities) are helping farmers decrease the nutrients that are excreted while maintaining or improving production and health. These feeding adjustments can help farmers reduce nitrogen excretions by 30-50% and phosphorous by 40-60% (Ludwig et al., 2013). The EQIP incentives payments and provided management practices help to cost share with the farm to help balance rations. Both Pennsylvania and New Jersey are including equine into these programs. They train feed nutritionists to help farm managers with developing feed management plans.


The horse farms varied in size from 6 to 99 horses and from 6 to 75 available acres on which manure could be applied. Two farms were in northern Virginia, one was in northern Maryland, and the remaining 20 farms were in Pennsylvania. Three farms were solely breeding farms while the other 20 boarded, trained, provided lessons, or offered some combination. Thirteen farms were willing to participate in the year-long total farm balance survey.

Survey 1 documented conservation and farm management practices on all 23 equine operations; quantitatively evaluated pasture desirable plants and canopy cover; sampled for analysis feed, hay, soil, manure, and compost; and conducted nutrient management audits using PA RUSLE2 (USDA NRCS, 2010). In addition, the research team tabulated pasture condition scores, pasture nutrient balancing sheets and PA Phosphorous-Index (Weld at. el, 2007). Pasture data, collected using line point transect methodology, included calculation of percent canopy cover, basal stems and desirable forage. All farms were supplied with farm specific BMPs suggestion in a written plan, that included: Manure Management Plan, Farm Grazing Plan, and the CAFO farms had plans written for them by a certified plan writer. The 23 surveyed operations were used to develop a baseline for total nutrient balances and levels for the Pennsylvania horse industry.

Survey 2 looked at nitrogen and phosphorus inputs on 13 farms to determine the risk of horse farms for non-point source pollution. Over a 12 month period, amounts of imported fertilizer, hay, concentrate feed, and bedding were obtained from farm managers. Samples of hay, concentrate feed, and bedding were taken from each farm and analyzed for N and P.  Whole farm nutrient balance was calculated as a percent by the equation ((imported nutrients- exported nutrients)/imported nutrients) X 100. Nitrogen and phosphorus whole farm balances were recorded on a percentage basis for the total farm and on a kilogram basis for per animal unit and per hectare values. One animal unit was defined as 1000 lbs. of live animal. SAS 9.2, PROC SURVEYMEANS was used to determine descriptive statistics on the sample and whole farm balance values. PROC MIXED runs an analysis of variance test with fixed and random effects to determine if there is statistical difference between means, while the Tukey test determines between which means there is a difference.

All soil, manure, bedding and compost samples were analyzed by Analytical Services Lab, University Park PA 16802. All feed samples were analyzed by the Dairy One Forage Laboratory in Ithaca, NY (Dairy One, 2009).

Results and Discussion

Survey 1: All of the 23 farms enlisted worked with the Extension Team to select and implement one or more Best Management Practices (BMPs) on their farm. BMP’s were chosen to increase pasture canopy cover and improve pasture quality, proper composting and/or disposal of manure, and ration formulation. In addition to proper management of manure and ration formulation, practicing rotational grazing, utilizing sacrifice areas, soil testing and applying lime and fertilizers are BMPs farmers were encouraged to adopt.

The 23 surveyed farms have helped to validate and evaluate existing tools on horse operations. The “pasture sediment loss” tools used (at that time) in this project (PA RUSLE2, Pasture Condition Score, Nutrient Balancing, Pasture Nutrient Balancing sheets and PA Phosphorous-Index) helped to analyze the effectiveness and sustainability of the nutrient reduction strategies. The survey results have shown that these selected tools needed to be adjusted in order to properly measure sediment and soil loss on horse farms.  

Smaller farm operators reported a major hurdle to managing pastures is lack of knowledge and lack of equipment. In addition, 33% of farm managers reported they wanted to utilize the suggested practices, but required financial assistance or more technical information.

Results of the information gathered by this Equine Extension team’s surveys has been used and examined by state agencies, assisting in development of in-service training for their personnel, used in revising potential regulations and assistance concerning horse farm operations.

Survey 2: Fresh feces, composted manure, hay, concentrate and soils were sampled on all 23 farms. Rations were evaluated on the farms for crude protein (CP) and P content according to NRC (2007) Nutrient Requirements for Horses.

Ration Evaluation: Based on estimated daily hay and concentrate intakes, crude protein and P amounts relative to NRC (2007) requirements differed significantly among production types (Table 1). The average CP feeding rate for maintenance horses was 173% of NRC, which differed (P < 0.05) from that of working horses, which were fed 152% of NRC. The average CP feeding rate for growing horses at 126% of NRC was also different (P < 0.02) from maintenance horses. Similarly, the average P feeding rate for maintenance horses at 229% of NRC differed (P < 0.003) from working horses which averaged a rate of 166% of NRC. The average P feeding rate of maintenance horses was also higher (P < 0.0001) than growing horses which were fed 156% of NRC.


Table 1. LS means of horse ration crude protein, phosphorus, and digestible energy, as a percent of the NRC 2007 Nutrient Requirements for Horses, according to horse production type from 23 surveyed horse farms. Means within a row having different letters are significantly different (P < 0.05).



Growing Working




Working   (n=92)


% of NRC

% of NRC

% of NRC

% of NRC

% of NRC

% of NRC

 Crude Protein

126 a

166 ab

173 b

138 ab

134 ab

152 a


156 a

268 ab

229 b

193 ab

180 ab

166 a

 Digestible   Energy

99 a

131 ab

128 b

127 ab

98 ab

104 a


Overall, crude protein as a percent of the NRC requirements ranged from 78% to 263% with a mean ± S.D. of 161±36% for all rations evaluated. Similarly, P ranged from 102% to 364% with a mean of 184±48%. Horses at a maintenance nutrient requirement level had the highest ration nutrient excesses averaging 173% N of NRC and 229% P of NRC.   

Manure and Compost:  Descriptive statistics of the fresh feces and stockpiled manure data sets are presented in Table 2. Fresh feces averaged 8.3 lbs. N/ton with 0.4 lbs. NH4/ton and 9.2 lbs. P2O5 with 6,522 mg/kg of water-extractable P. Stockpiled manure averaged 12.9 lbs. N/ton with 0.8 lbs. NH4/ton and 7.9 lbs. P2O5 with 1,460 mg/kg of water-extractable P. Phosphorus source coefficient scores indicate the potential of P to be extracted by water and contribute to runoff pollution and they are measured on a scale from 0 to 1. Those scores were higher for fresh feces, at 0.73, than stockpiled manures at 0.18. 


Table 2. Nutrient characteristics of equine fresh feces and stockpiled manure from 23 surveyed horse farms. Means within a column having different letters are significantly different (P < 0.05).

Total N
Organic N



Mean n=25


23.2 a

8.3 a

0.4 a

7.9 a

9.2 a

7.1 a

6522.0 a

0.73 a

Std Dev.










Mean n=25


44.5 b

12.9 b

0.8 a

12.1 b

7.9 a

17.2 b

1460.2 b

0.18 b

Std Dev.










                                 1Water-extractable phosphorus
                                 2Phosphorus source coefficient score
                                 3Feces samples were deemed excreted less than 24 hrs. prior and contained no urine or bedding.
                                4Manure samples were taken from manure storage areas containing feces, urine, and bedding


Soil Tests: The farms' soil P ranged from 7- 432 ppm and averaged 71 ppm. Soil P saturation percentage was calculated by the equation [Soil P (mmole/kg)/ {Soil Al (mmole/kg) + Soil Fe (mmole/kg)}] X 100. The mean soil P saturation percentage of all the farms was 7.9 % and five (22%) of the farms had samples over the environmental threshold of 15%. Average soil test values from 23 horse farms can be seen in Table 3.


Table 3. Soil test values from 23 horse farms.

Soil pH
Soil P
Soil K
Soil Mg
Soil Al
Soil Fe








Mean n=65








Std Dev.








                            1P-saturation = [Soil P (mmole/kg)/ {Soil Al (mmole/kg) + Soil Fe (mmole/kg)}] X 100


Whole Farm Nutrient Balance: The majority of the horses on the farms were non-breeding horses, for which the only managed output was manure. On the 13 farms studied for whole farm balance, 4 of the farms did not export any manure, 3 exported a small portion of their collected manure and 6 exported all their collected manure. Whole farm balance inputs (Table 4) averaged 53 kg N per 1000 lbs of animal (AU) and 13 kg P/AU. Whole farm balances ranged from 100% retention of imported nutrients where no products were exported to a negative balance where all collected manure was exported. Average N and P whole farm balances were 73% and 45% retention of inputs, respectively. With limited export of nutrients from horse farms in foals or manure, more manure must be exported and/or nutrient imports must be decreased to approach nutrient balance and decrease the risk of nutrient pollution.  Boarding and training horse farms have no physical product output such as milk or meat, so only manure nutrient exports were included in the calculation of nutrient output. 


Table 4. Annual nitrogen and phosphorus inputs per animal unit (AU) and hectare (ha) of 13 Chesapeake Bay Watershed horse farms; means ± standard deviation.

 Kg N/AU/yr.

 Kg P/AU/yr.

 Kg N/ha/yr.

 Kg P/ha/yr.

53 ± 14.6

13.2 ± 4.1

168 ± 145.1

32.9 ± 34.6


This study found, on these horse farms, the average of the whole farm balances was 73% for N and 45% for P; this was similar to findings in other species. Koelsch (2005) reported whole farm N balances on dairy farms which ranged from 59-86% and whole farm P balances on beef feed lots which ranged from 36-66%. To compare yearly horse farm N and P inputs /AU and land mass to other published dairy, hog, and poultry values see Table 5. However, on horse farms, there is a wide range of values for whole farm balance nutrient mainly due to the amount of manure horse farms export. In this study, horse farms exporting all of their manure averaged 39% balance for N and -27% for P; and they reported all farms imported some feed. The mean farm balance for those that did not export any manure was 100%. This shows that horse farms can achieve a whole-farm balance of N and P.


Table 5. Annual horse farm nitrogen and phosphorus inputs per animal unit (AU) and hectare (ha) compared to published dairy, hog, and poultry values.

 Farm Type

Kg N/AU/yr.

Kg P/AU/yr.

Kg N/ha/yr.

Kg P/ha/yr.


53 ± 14.61

13.2 ± 4.11

168 ± 145.11

32.9 ± 34.61


55.33, 152.63

143, 23.43, 14.42

633, 2353

163, 363, 462


228.53, 236.13

41.63, 453

3523, 3993

643, 763






                                             aMean ± Standard Deviation, bMeans
                                1Current Study
                                              2Source: Tarkalson and Mikkelsen, 2003. 
                                              3Source: Nielsen and Kristensen, 2005.


Manure must be exported and/or fewer feed related nutrients must be imported to approach nutrient balance on horse farms. Hauling manure off the property can improve farm balance although neighboring crop farms have to be willing to work with the producer (Koelsch, 2005). It has been reported that most horse farms export nearly 50% of their manure (Swinker at. el, 2011). Fifty-four percent of all horse farms spread manure on their farms (Westendorf, at. el, 2010).


The Extension team noted that farm owners are committed to adopting practices that maintain healthy horses, healthy farms, and a healthy environment. The horse farms included in this survey do not appear to pose a major environment concern to the Chesapeake Bay. Horse numbers per farm were low at 25 horses per farm, soil P tests were generally below an environmental threshold and perennial grass pastures usually protected water quality.  Improving pasture production and utilization along with reducing CP and P concentrations in rations may help reduce nutrient imports, and the risk of nutrient pollution.

The survey results are being used in the development of the curriculum for Environmental Stewardship short courses, to help agency personal understand the equine industry and to help farm owners develop the knowledge and skills necessary to adopt environmentally sound farm management practices.


Literature Cited

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Dairy One. (2009). Forage lab analytical procedures. Retrieved from:

Koelsch R. (2005). Evaluating livestock system environmental performance with whole-farm nutrient balance. Journal of Environmental Quality, 34:149–155.

Koelsch, R. and Lesoing, G. (1999). Nutrient balance on Nebraska livestock confinement systems. Journal of Animal Science 1999. 77:63-71.

Lanyon, L.E., and Beegle, D.B. (1989). The role of on-farm nutrient balance assessments in an integrated approach to nutrient management. Journal of Soil and Water Conservation 44(2):164-168.

Ludwig, D., Ishler, V. and White, R. (2013). Feed management planners certification program to reduce nutrient loads in impaired watersheds.  Retrieved from:

Nielsen, A. H., and Kristensen, I.S.. (2005). Nitrogen and phosphorus surpluses on Danish dairy and pig farms in relation to farm characteristics. Livestock Production Science 96:97–107.

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National Research Council. (2007). Nutrient requirements of horses. 7th ed. National Academy Press, Washington, DC.

Rotz, C.A. (2004). Management to reduce nitrogen losses in animal production. Journal of Animal Science. 82(E. Suppl.):E119–E137.

Swinker, A. M. (2013). SARE Project, Development and Implementation of and Equine Environmental Stewardship Program, Final Report, Retrieved from:

Swinker, A., Worobey, S., McKernan, H., Meinen, R., Kniffen, D., Foulk,D., Hall, M., Weld, J., Schneider, F., Burk, A., Brubaker, M. (2011). Profile of the Equine Industry’s Environmental, Best Management Practices and Variations in Pennsylvania, Journal of Equine Veterinary Science. 30:44176.

Tarkalson, D. D., and Mikkelsen, R.L. (2003). A phosphorus budget of a poultry farm and a dairy farm in the southeastern U.S., and the potential impacts of diet alterations. Nutrient Cycling in Agroecosystems 66: 295–303.

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Weld. J., Beegle D., Bryant, R., Gburek, W., Kleinman, P., and Sharpley, A. (2007). The Pennsylvania phosphorus index: Version 2. Penn State College of Agricultural Sciences, Agricultural Research and Cooperative Extension Publication CAT UC180, University Park, Pennsylvania.

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