84 Pasture production in integrated warm- and cool-season grass equine rotational pasture systems

Abstract

Incorporating warm-season grasses (WSG) into traditional cool-season (CSG) rotational pastures has been utilized to increase summer forage available for grazing cattle. The aim of this study was to evaluate the impact of this practice on yield and nutritive value of horse pastures. We hypothesized WSG incorporation would increase summer pasture yield, while being lower in non-structural carbohydrates (NSC). Two 1.5 ha rotational systems (6–0.25 ha sections/system) were utilized: a control system (CON) with all sections containing an established CSG mix (Kentucky bluegrass, orchardgrass, and tall fescue), and an integrated system (IRS) [3 CSG sections (CSG-IRS) and 3 Quick-N-Big crabgrass (CRB-IRS)]. Three horses per system grazed across 3 periods: EARLY (mid-May to mid-Jul), SLUMP (mid-Jul to mid-Sep), and LATE (mid-Sep to mid-Nov). Horses were confined to dry lots if sufficient pasture forage was not available. Before each rotation, herbage mass (HM) was measured and forage samples collected (0800–1000) with nutrients analyzed by wet chemistry. Grazing days were tracked to calculate carrying capacity (CC). Data were analyzed by ANOVA and means separated by Tukey's method in R. Over the full grazing season, IRS provided pasture access for 123 d, while CON supported grazing for 104 d (69% and 59% of total). Total HM per section did not differ during EARLY grazing when CRB was not available (CSG-IRS: 2537 ± 605; CSG-CON: 3783 ± 856 kg/ha), but CC was greater in CSG-IRS (220 ± 37 horse d/ha) than in CSG-CON (92 ± 26 horse d/ha; P = 0.03). In SLUMP grazing, both HM and CC were greater in CRB-IRS (HM: 4758 ± 698 kg/ha; CC: 196 ± 31 horse d/ha) than either CSG-IRS (HM: 1086 ± 698 kg/ha; CC: 32 ± 31 horse d/ha) or CON (HM: 970 ± 493 kg/ha; CC: 46 ± 22 horse d/ha; P < 0.02). While HM did not differ by section type in LATE grazing (1284 ± 158 kg/ha), CC was greater in CON (84 ± 9 horse d/ha) vs CRB-IRS (32 ± 13 horse d/ha; P = 0.03) and CSG-IRS (40 ± 13 horse d/ha; P = 0.06). During the SLUMP, water-soluble carbohydrates (WSC) were lower in CRB-IRS (4.46 ± 0.80%) than CSG-CON (7.92 ± 0.90%; P < 0.04), but not CSG-IRS (5.93 ± 1.04%); however, non-structural carbohydrates (NSC) did not differ (7.05 ± 0.62%). There were no differences in either WSC (6.46 ± 0.54%) or NSC (7.65 ± 0.54%) by section type in LATE grazing. These results demonstrated increased summer horse pasture yield through integrated grazing, but further research is needed to improve late-season production. Additionally, integrated grazing provided lower WSC to grazing horses, but NSC remained below 10% for all pasture sections.