title: Protein quality and utilization of timothy, oat-supplemented timothy, and alfalfa at differing harvest maturities in exercised Arabian horses.
abstract: To evaluate the protein quality and postgut N utilization of full-bloom timothy hay, oat-supplemented timothy-hay diets, and alfalfa hay harvested at different maturities, apparent whole tract N digestibility, urinary N excretion, and serum AA profiles were determined in light to moderately exercised Arabian horses. Six Arabian geldings (16.0 ± 0.3 yr; 467 ± 11 kg of BW) were randomly allocated to a 6 × 6 Latin square design. Diets included full-bloom timothy grass hay (G), G + 0.2% BW oat (G1), G + 0.4% BW oat (G2), mid-bloom alfalfa (A1), early-bloom alfalfa (A2), and early-bud alfalfa hay (A3). Forages were fed at 1.6% of the BW of the horse (as-fed). Each period consisted of an 11-d adaptation period followed by total collection of feces and urine for 3 d. Blood samples were taken on d 11 for analysis of serum AA concentrations. During the 3-d collection period, urine and feces were collected every 8 h and measured and weighed, respectively. Approximately 10% of the total urine volume and fecal weight per period was retained for N analyses. Fecal DM output was less (P < 0.05) in A1, A2, or A3 compared with G, G1, or G2. Apparent whole tract N digestibility was greater (P < 0.01) in A1, A2, and A3 compared with G, G1, or G2, and was greater (P < 0.05) in G1 and G2 compared with G. Nitrogen retention was not different from zero, and there were no differences (P > 0.05) in N retention among diets. Urinary N excretion and total N excretion were greater (P < 0.05) in A1, A2, and A3 compared with G, G1, or G2. Plasma concentrations for the majority of AA increased curvilinearly in response to feeding G, A1, A2, and A3 (quadratic, P < 0.05), with values appearing to maximize 2-h postfeeding. Although alfalfa N digestibility increased with decreasing harvest maturity, N retention did not differ and urinary volume and N excretion increased, indicating that postabsorptive N utilization decreased. In contrast, inclusion of oats at either 0.2 or 0.4% of the BW of the horse to timothy hay markedly enhanced N digestibility without increasing N excretion, indicating improvement in postgut N utilization. These findings indicate that feeding oat-supplemented timothy hay is more environmentally sustainable than feeding alfalfa to the horse at maintenance or under light to moderate exercise.
authors.affiliation: Department of Animal Science, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: Woodward
authors.forename: B D
authors.initials: BD
authors.lastname: Nielsen
authors.forename: J
authors.initials: J
authors.lastname: Liesman
authors.forename: T
authors.initials: T
authors.lastname: Lavin
authors.forename: N L
authors.initials: NL
authors.lastname: Trottier
mesh_terms: D000821:Animal Feed / Q000032:analysis* / Q000592:standards; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001120:Arginine / Q000097:blood; D018592:Cross-Over Studies; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000032:analysis / Q000378:metabolism*; D006736:Horses / Q000502:physiology*; D008297:Male; D000455:Medicago sativa / Q000737:chemistry*; D010805:Physical Conditioning, Animal; D006109:Poaceae / Q000737:chemistry*; D013997:Time Factors
chemical_list: D004044:Dietary Proteins; D001120:Arginine