Diurnal Variation in Forage Nutrient Composition of Mixed Cool-Season Grass, Crabgrass, and Bermudagrass Pastures

Warm-season grasses have been suggested as alternative low non-structural carbohydrate (NSC) pasture forages. The purpose of this study was to evaluate nutrient composition and diurnal changes in soluble carbohydrates for the warm-season annual 'Quick-N-Big' crabgrass [CRB; Digitaria sanguinalis (L.) Scop.] and the warm-season perennial 'Wrangler' bermudagrass [BER; Cynodon dactylon (L.) Pers] in comparison to mixed cool-season grass [CSG; 'Inavale' orchardgrass (Dactylis glomerata [L.]), 'Tower' tall fescue (Lolium arundinaceum [Schreb.] Darbysh.), and 'Argyle' Kentucky bluegrass (Poa pratensis [L.])]. Samples were collected at 4-hour intervals over 3 d when each forage reached the boot stage of maturity. Digestible energy was greatest for CSG (2.29 ± 0.34 Mcal/kg) and lowest for BER (2.13 ± 0.34 Mcal/kg), while crude protein was lowest for CSG (16.1 ± 0.29%) and neutral detergent fiber was greatest for BER (60.0 ± 0.41; P ≤ .0008). Non-structural carbohydrates were greater for CSG (17.6% ± 0.26%) compared to BER (10.6% ± 0.26%) or CRB (10.9% ± 0.26%; P < .0001). Overall, NSC was greatest in the afternoon and evening (14.5-14.9 ± 0.60%) and lowest in the early morning (11.2-11.4 ± 0.60%; P ≤ .04), but diurnal variation was most pronounced in CSG versus either Warm-season grasses. Results of this study provide needed data on nutritional composition of CRB and BER and demonstrate that these grasses may serve as pasture forages for horses where NSC intake is of concern. Results also support recommendations for restricting grazing to early morning to limit NSC consumption, particularly in CSG pastures.