Yield, nutrient composition, and horse condition in integrated crabgrass and cool-season grass rotational grazing pasture systems

Integration of warm-season grasses into traditional cool-season pastures can increase summer forage for grazing cattle. The aim of this study was to determine impacts of this practice on yield and nutrient composition of equine rotational pasture systems as well as horse body condition. Two 1.5 ha rotational systems (6 to 0.25 ha sections/system) were evaluated: a control system (CON) (all sections mixed cool-season grass [CSG-CON]) and an integrated rotational grazing system (IRS) (three CSG sections [CSG-IRS] and three Quick-N-Big crabgrass [Digitaria sanguinalis (L.) Scop.; CRB-IRS]). Three horses per system grazed in three periods: EARLY (mid-May to mid-July), SLUMP (mid-July to mid-September), and LATE (mid-September to mid-November). Herbage mass (HM) was measured prior to each rotation and samples were collected (0800 to 1000 h) for nutrient analysis. Grazing days were tracked to calculate carrying capacity (CC). Horse condition measures were assessed monthly. Over the full grazing season, 9,125 kg of forage was available for grazing in IRS versus 6,335 kg in CON. The CC was 390 horse d for IRS, while only 276 horse d for CON. Total HM/section did not differ during EARLY when CRB was not available (CSG-IRS: 2,537 +/- 605; CSG-CON: 3,783 +/- 856 kg/ha), but CC was greater in CSG-IRS (220 +/- 37 horse d/ha) than CSG-CON (92 +/- 26 horse d/ha; P = 0.03). In SLUMP, both HM and CC were greater in CRB-IRS (HM: 4,758 +/- 698 kg/ha; CC: 196 +/- 31 horse d/ha) than CSG-IRS (HM: 1,086 +/- 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 (1,284 +/- 158 kg/ha), CC was greater in CSG-CON (84 +/- 9 horse d/ha) versus CRB-IRS (32 +/- 13 horse d/ha; P = 0.03) and CSG-IRS (40 +/- 13 horse d/ha; P = 0.06). During 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 WSC (6.46% +/- 0.54%) or NSC (7.65% +/- 0.54%) by section type in LATE. Horses in IRS maintained a body condition score (BCS) of 5.78 +/- 0.48, but BCS did not differ by system (CON: 6.11 +/- 0.48). Thus, integrated grazing increased summer pasture yield and provided adequate nutrition to maintain horse condition, but further research is needed to improve late-season production. Integrated grazing may not, however, provide an advantage in limiting dietary NSC, as NSC remained low for all pasture sections.