50 Intake, digestibility, and nitrogen balance in horses fed rhizoma peanut hay

Abstract

Rhizoma peanut hay has the potential to meet horses’ crude protein requirements with reduced nitrogen excretion. This study aimed to evaluate nutrient intake, apparent digestibility, and nitrogen balance of rhizoma peanut (RP, Arachis glabrata cv Florigraze) hay compared with alfalfa (ALF, Medicago sativa L. cv Legendary XHD) and bermudagrass (CB, Cynodon dactylon L. cv Coastal) hays when fed to maintenance horses at 2% BW/d on a dry-matter (DM) basis. Six mature Quarter Horse geldings (593 ± 40 kg; mean ± SD) were randomly assigned to one of the hays in a replicated 3 × 3 Latin square with 21-d periods. A 14-d adaptation phase was followed by a 3-d total fecal and urine collection. Intake of nutrients is reported on a DM basis. Both legumes (ALF = 1.99% BW and RP = 1.97% BW) provided DM intake greater ( P < 0.05) than CB (1.82% BW) but were not different from one another. Digestible energy (DE) intake of ALF (29.9 Mcal/d) and RP (29.4 Mcal/d) were greater ( P < 0.05) than CB (20.8 Mcal/d). Crude protein (CP) intake was greater ( P < 0.05) for ALF (2,542 g/d), followed by RP (1,859 g/d), and then CB (1,477 g/d). Alfalfa provided the highest ( P < 0.05) calcium to phosphorus ratio of 6.3:1, while RP provided 4.4:1, and CB provided the lowest (1.7:1). Intake of all hays exceeded maintenance DE, CP, Ca, and P requirements. Apparent DM ( P < 0.05) and CP ( P < 0.05) digestibility were greater for ALF (69%, 84%), followed by RP (61%, 72%), and lowest for CB (46%, 64%). Neutral detergent fiber apparent digestibility did not differ ( P = 0.2228) among the 3 hays, while acid detergent fiber digestibility ( P = 0.0054) was lower for RP and similar for ALF and CB. Apparent digestibility of non-structural carbohydrate ( P < 0.05) was greater for ALF, followed by RP, and lowest for CB, while starch ( P < 0.05) digestibility was similar between the legumes and lowest for CB. Water intake for ALF was greater ( P < 0.05) than RP and CB. Greater urinary excretion ( P < 0.05) was observed for alfalfa, while water excreted through feces was greater ( P < 0.05) for CB, followed by RP, and lower for ALF. Urinary nitrogen (N) excretion was greater ( P < 0.05) for ALF, followed by RP, and lower for CB whereas fecal N excretion for both RP and CB were greater ( P < 0.05) than for ALF. Total N excreted was greater ( P < 0.05) for ALF (278 g/d), followed by RP (211 g/d), and lower for CB (179 g/d). Nitrogen retention was greater ( P < 0.05) for ALF when represented as g/d, but similar to RP when presented as percent of N intake. Results indicate that rhizoma peanut hay is a suitable legume for horses by meeting DE and CP requirements with significantly less N excretion than alfalfa.