Effects of 27 mo of rotational vs. continuous grazing on horse and pasture condition

Abstract

The objective of this study was to determine whether rotational grazing generates horse, pasture, or cost benefits over continuous grazing. The study established two replicates (1.57 ha each) of rotational (R; four grazing sections and a stress lot per replicate, where horses were fed a moderate quality grass hay at 2% of body weight when not grazing) and continuous (C) grazing systems (treatments). Twelve Standardbred mares were grazed for an overall stocking rate of 0.52 ha/horse (n = 3 in each pasture). Recommended management practices for each grazing system were followed for 27 mo including three grazing seasons. Samples were collected monthly between 0800 and 1000. Results were analyzed in SAS (V9.4) using mixed model repeated-measures analysis of covariance, chi-square tests of association, and two-sample t-tests. Alpha level was set at P < 0.05. The C horses were maintained on pasture for 100% of the study duration (844 d; August 1, 2014 to November 22, 2016), while R horses had access to pasture for approximately half of this time (408 ± 33 d). The average length of grazing bout per rotational grazing section during the grazing season increased numerically each year from 7.88 ± 0.76 d in 2014, 10.0 ± 0.61 d in 2015, and 10.9 ± 0.80 d in 2016. Average horse body condition score (BCS) and body fat differed by treatment, with C horses (BCS 6.3 ± 0.05, 17.9 ± 0.15% body fat) greater than R horses (BCS 5.9 ± 0.05, 16.8 ± 0.15% body fat). Both sward height and herbage mass were greater in R (11.8 ± 0.1 cm tall; 1,513 ± 41 kg/ha) than C pastures (6.9 ± 0.1 cm tall; 781 ± 35 kg/ha). The R pastures had higher proportions of vegetative and total cover, planted grasses (tall fescue and orchardgrass), and weeds but lower proportions of grass weeds (nonplanted grasses) and other (rocks, litter, bare ground, etc.) as compared with C pastures. Digestible energy, acid detergent fiber, and calcium were higher in R vs. C pastures; however, crude protein was lower in R vs. C pastures. There were no significant differences between treatments for average monthly amount of hay fed (C, 597 ± 34.1 vs. R, 659 ± 34.1 kg) or average monthly pasture maintenance cost (C, $17.55 ± 3.14 vs. R, $20.50 ± 3.14). This study is one of few replicated experiments comparing the effects of rotational and continuous grazing for horses on pasture quality, horse condition, and production costs. The results here support the recommendation of rotational grazing for production, environmental, and ecological purposes.

Keywords: continuous grazing; equine; herbage mass; pasture; rotational grazing; sward height.