Why Look at Rotations Grazing in Horse Pastures?
Rotational grazing is a recommended strategy to improve pasture health and animal performance. Previous studies have reported improved forage quality in rotationally grazed pastures compared to those continuously grazed by cattle, but data are limited for horse pastures.
What did we do?
A study at the University of Tennessee was conducted to evaluate the effects of rotational grazing on the nutrient content of horse pastures. A 2.02 ha rotational grazing pasture (RG) and a 2.02 ha continuous grazing pasture (CG) were each grazed by three adult horses at a stocking rate of 0.6 ha/horse over a two year period. The RG system was divided into four 0.40 ha paddocks and a heavy use area. Pastures were maintained at uniform maximum height of 15 to 20 cm by mowing. Horses were rotated between the RG paddocks every 10 to 14 d, or when forage was grazed to a height of approximately 8 cm. Pasture forage samples (n = 520) were collected and composited monthly (n = 14) during the growing season (April to November) by clipping forage from randomly placed 0.25 m2 quadrates from RG and CG, as well as before and after grazing each RG paddock. Botanical composition and percent ground cover were visually assessed. Forage samples were oven dried at 60°C in a forced air oven for 72 h to determine DM. Forage biomass yield (kg/ha), digestible energy (DE, Mcal/kg), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin, calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), ash, fat, water soluble carbohydrates (WSC), sugar and fructan were measured using a FOSS 6500 near-infrared spectrometer. Data were analyzed using paired T-tests and differences were determined to be significant at P < 0.05. Data are reported as means ± SEM as a percent of DM.
What have we learned?
| Table 1. Nutrient content of continuously grazed (CG) pasture and rotationally grazed (RG) pasture. Data are summarized as means ± SE. | ||
|---|---|---|
| Nutrient | Continuous | Rotational |
| DM, % | 91.72 ± 0.36 | 91.89 ± 0.34 |
| DE, Mcal/kg | 2.31 ± 0.064 | 2.42± 0.039* |
| CP, % | 14.92 ± 0.77 | 15.79 ± 0.64 |
| ADF, % | 33.16 ± 1.21 | 30.81 ± 0.82* |
| NDF, % | 56.80 ± 1.75 | 53.53 ± 1.65* |
| Lignin, % | 3.47 ± 0.38 | 2.88 ± 0.32* |
| Ca, % | 0.69 ± 0.11 | 0.68 ± 0.11 |
| P, % | 0.25 ± 0.009 | 0.27 ± 0.008* |
| K, % | 1.92 ± 0.10 | 2.11 ± 0.087* |
| Mg, % | 0.25 ± 0.009 | 0.26 ± 0.007 |
| Ash, % | 9.35 ± 0.83 | 9.39 ± 0.66 |
| Fat, % | 2.65 ± 0.12 | 2.83 ± 0.08 |
| WSC, % | 4.95 ± 0.60 | 6.72 ± 0.71* |
| Sugar, % | 3.33 ± 0.50 | 4.86 ± 0.55* |
| Fructan, % | 1.61 ± 0.15 | 1.59 ± 0.16 |
| *means within rows differ; P < 0.05 | ||
Forage biomass yield did not differ between RG and CG (2,125 ± 52.2; 2,267 ± 72.4 kg/ha, respectively). The percentage of grass species was greater in RG compared to CG (81.7 ± 3.9; 73.9 ± 4.5, respectively) and the percentage of weed species was lower in RG compared to CG (3.4 ± 0.8; 12.0 ± 1.5, respectively). Tall fescue, kentucky bluegrass, bermudagrass and white clover were the dominant forage species. Rotational grazing increased forage quality compared to continuous grazing. The RG system was higher in DE (Mcal/kg), phosphorous (P), potassium (K), water soluble carbohydrates (WSC), and sugar compared to the CG system (Table 1). While there wasn’t a significant difference in crude protein (CP) content between RG and CG, the numerical difference could potentially affect animal performance. The RG pasture was lower in acid detergent fiber (ADF), neutral detergent fiber (NDF) and lignin compared to the CG pasture. Within the RG pasture, forage nutrient content declined following a grazing period, but recovered with rest. Paddocks were lower in DE, CP, P, K, Fat, WSC and sugar while they were higher in ADF and NDF after grazing compared to before grazing (Table 2).
| Table 2. Nutrient content of rotational grazing (RG) paddocks before and after grazing. Data are summarized as means ± SE. | ||
|---|---|---|
| Nutrient | Before | After |
| DM, % | 91.84 ± 0.27 | 91.84 ± 0.39 |
| DE, Mcal/kg | 2.34 ± 0.03 | 2.21 ± 0.02* |
| CP, % | 14.98 ± 0.39 | 13.71 ± 0.43* |
| ADF, % | 32.24 ± 0.54 | 34.33 ± 0.48* |
| NDF, % | 55.97 ± 0.88 | 59.24 ± 0.89* |
| Lignin, % | 2.79 ± 0.20 | 3.41 ± 0.25* |
| Ca, % | 0.58 ± 0.05 | 0.59 ± 0.05 |
| P, % | 0.28 ± 0.004 | 0.25 ± 0.006* |
| K, % | 2.11 ± 0.08 | 1.72 ± 0.07* |
| Mg, % | 0.26 ± 0.007 | 0.26 ± 0.009 |
| Ash, % | 8.76 ± 0.19 | 8.79 ± 0.21 |
| Fat, % | 2.64 ± 0.05 | 2.45 ± 0.06* |
| WSC, % | 6.05 ± 0.47 | 4.85 ± 0.39* |
| Sugar, % | 4.40 ± 0.38 | 3.22 ± 0.30* |
| Fructan, % | 1.67 ± 0.15 | 1.69 ± 0.16 |
| *means within rows differ; P < 0.05 | ||
Future Plans
Rotational grazing may be a preferred alternative to continuous grazing as it favors grass production, suppresses weeds and increases energy and nutrient content of pastures. While rotational grazing may be beneficial from an environmental and animal production standpoint, an increase in DE and WSC may pose a risk for horses prone to obesity and metabolic dysfunction. Appropriate precautions should be taken in managing at risk horses under rotational grazing systems. This work is being continued at Virginia Tech and other universities to further understand the use of rotational grazing systems for horses.
Authors
Bridgett McIntosh, Equine Extension Specialist, Virginia Tech bmcintosh@vt.edu
Matt Webb, Ashton Daniel, David McIntosh and Joe David Plunk, University of Tennessee
Additional information
http://www.arec.vaes.vt.edu/middleburg/
Acknowledgements
The authors thank the University of Tennessee Middle Tennessee Research and Education Center and the Tennessee Department of Agriculture’s Nonpoint Source Pollution 319 Water Quality Grant for their support of this project.
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