rotational grazing – Livestock and Poultry Environmental Learning Community

Purpose

This presentation will review the existing multi-species literature on nutrient cycling and how it is affected by the horse’s diet and rotational grazing.

Grazed pastures, particularly rotationally grazed pastures, recycle nutrients faster than ungrazed pastures. Nutrients on pasture land enter through animal waste, and waste feed or fertilizer; they leave through removal of forage, leaching/runoff, or animal product/waste removal. Taking away the animal component removes about half of the inputs needed to recycle the nutrients. Dietary nitrogen (N), phosphorus (P) and potassium (K) are required for basic maintenance of horses; however, not all of what is consumed is used by the animal, therefore the dietary concentrations of these nutrients will impact the nutrient cycling. Digestibility of N, P and K in horses is approximately 80, 25 and 75 %, respectively. What does not get digested will end up excreted back into the soil.

What did we do?

For example, in one study eight Standardbred mares were divided into two groups and received diets of grass hay and grain. The high P (HP) group received 142 g/d of NaH2PO4, formulated to provide 4.5-times the dietary P requirement, or 65 g phosphorus/d. The low P (LP) group received 28 g of phosphorus/d in the basal diet. Data showed that horses receiving the HP diet excreted higher P and water extractable P in the manure than those fed the LP diet (Table 1; Westendorf and Williams, 2015). The same goes for N, where one study used a treatment group that was supplemented with 700 g/d of soybean meal top dressed on 500 g of sweet feed per day (TRT; 1042 g protein/d DM total), while the control group received the sweet feed meals without the soybean meal (CON; 703 g protein/d total). Both groups were also fed 8 kg/d of a grass hay mix (562 g protein /d DM), water and salt ad libitum. Horses fed the TRT diet excreted more N and NH3 than horses fed the CON diet (Figure 1; Williams et al., 2011).

What have we learned?

More intensive grazing also creates an increased rate of nutrient cycling due to the added animal inputs on the land. Even though no horse related studies have been performed on this topic studies in cattle have found that plant-available N levels doubled when cattle were rotationally grazed with five grazings per season instead of three (Baron et al., 2002). Kenny (2016) looked at horses grazed under either a continuous or rotational grazing system (see Pictures 1 and 2, Left to Right, respectively) and found no differences in system after one year of grazing, however, the author concludes that more time on the system could have generated differences.

Other factors that affect the rate of nutrient cycling include amount of legumes in the pasture, distribution of manure on pastures (i.e. relation to water, shelters and fencing), and use or rates of fertilizer.

Future Plans

More equine specific studies need to be performed looking at how grazing systems and equine diets affect nutrient cycling and how horse farm owners can utilize this to best manage their farm for optimal nutrient utilization.

Corresponding author, title, and affiliation

Carey A. Williams, Equine Extension Specialist, Rutgers, the State University of New Jersey, Department of Animal Science

Corresponding author email

carey.williams@rutgers.edu

Additional information

References:

Baron, V. S., E. Mapfumo, A. C. Dick, M. A. Naeth, E. K. Okine, and D. S. Chanasyk. 2002. Grazing intensity impacts on pasture carbon and nitrogen flow. J. Range Manage. 55:525-541.

Kenny, L. B. 2016. The Effects of Rotational and Continuous Grazing on Horses, Pasture Condition, and Soil Properties. Master thesis, Rutgers, the State University of New Jersey, New Brunswick, NJ.

Westendorf, M. L., and C. A. Williams. 2015. Effects of excess dietary phosphorus on fecal phosphorus excretion and water extractable phosphorus in horses. J. Equine Vet. Sci. 35:495-498. doi:10.1016/j.jevs.2015.01.020

Williams, C. A., C. Urban, and M. L. Westendorf. 2011. Dietary protein affects nitrogen and ammonia excretion in horses. J. Equine Vet. Sci. 31:305-306.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2017. Title of presentation. Waste to Worth: Spreading Science and Solutions. Cary, NC. April 18-21, 2017. URL of this page. Accessed on: today’s date.

March 5, 2019March 6, 2019

Effect of Grazing Cell Size on Horse Pasture Utilization

Purpose *

Horses grazing continuously within a single pasture often graze selectively resulting in under- and over-grazed areas. The net result is inefficient use of forage and/or eventually loss of ground cover. This practice contributes negatively to pasture health and the environment. Rotational grazing can alleviate this problem by forcing horses to be less selective due to constraints on space and time allowed for grazing. It is generally accepted that grazing cells should be sized to provide enough forage for no more than 7 d in order to prevent selective grazing. However, little information is available to definitively confirm this maximum residence time. If the residence time could be increased to greater than 7 d by increasing the size of the grazing cell without the occurrence of selective grazing then labor inputs associated with reconstructing fences and moving horses could be reduced. A reduction in labor might also contribute to an increased acceptance of this practice among horse owners and managers. Therefore a study was designed to compare effect of increasing residence time by increasing grazing cell size on the level of grazing uniformity.

What did we do?

A predominately tall fescue pasture (approximately 1.5 ha; Lolium arundinaceum Schreb cultivar Max-Q; Pennington Seed, Madison, GA) was divided into four equal sub-plots (approximately 0.37 ha). Eight mature geldings (approximately 500 kg; 9.75 ± 4.4 yr) were paired and randomly assigned to one of two grazing regimes within subplots as follows to determine the effect of residence time and grazing cell size on pasture characteristics reflecting uniformity of grazing: 1) single large grazing cell (SLGC) where horses had access to the entire 0.37 ha subplot for 21-d, or 2) multiple small grazing cells (MSGC) where horses had access to approximately one-third (0.123 ha) of the 0.37 ha subplot for 7 d and were then moved to the next adjacent one-third of the subplot every 7-d for a total of 21-d. Subplot size was estimated to contain enough DM to support DM intake of 2.4% of BW/d for 21 d assuming a grazing efficiency of 0.7. Pasture herbage mass, sward height, compressed sward height and percent ground cover were determined on d-0 and d-21within each sub-plot. The percent compressed sward height below 5 cm within each subplot was used as an estimate of “over-grazed” area. Response variables were analyzed as a repeated measures design for treatment, time and treatment x time interactions. A P-value of 0.05 was considered significant; whereas a P-value of 0.1 was considered a tendency.

What have we learned?

Pasture herbage mass, sward height, compressed sward height and percent ground cover were not affected by treatment or treatment time interactions. Pasture herbage mass tended to decrease over time (P = 0.08). Sward height and compressed sward height decreased over time (P < 0.05). Percentage of compressed sward height below 5 cm tended to increase at a greater rate within MSGC as compared to SLGC (P = 0.07). Results of this study suggest that sizing grazing cells for longer residence times is feasible and that sizing grazing cells for a shorter residence time requires more management to insure overgrazing does not occur.

Future Plans

Although the results of this study suggests that two horses can graze a 0.37 ha area containing enough dry matter to facilitate 2.4% of BW intake (assuming a grazing efficiency of 0.7); it is unknown how increasing the stocking rate (and related grazing cell size) will affect uniformity of grazing. Future experiments will investigate this question.

Authors

Paul D. Siciliano, Professor, Dept. of Animal Science, North Carolina State University Paul_Siciliano@ncsu.edu

Jennifer Gill, Department of Animal Science, North Carolina State University

Additional information

Bott, R.C., Greene, E.A., Koch, K., Martinson, K.L., Siciliano, P.D., Williams, C., Trottier, N.L., Burke, A., Swinker, A. 2013. Production and environmental implications of equine grazing. J. Equine Vet. Sci. 33(12):1031-1043.

Acknowledgements

This project was supported by the North Carolina Agricultural Research Service.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.

March 5, 2019March 6, 2019

Rotational Grazing Effects on Pasture Nutrient Content

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.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.