Vitamin A depletion and repletion in thoroughbred horses

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dc.contributor.authorGreiwe-Crandell, Kathleen M.en
dc.contributor.committeechairKronfeld, David S.en
dc.contributor.committeememberBowen, John M.en
dc.contributor.committeememberHerbein, Joseph H. Jr.en
dc.contributor.committeememberJack, Nancy E.en
dc.contributor.committeememberKnight, James W.en
dc.contributor.committeememberLey, William B.en
dc.contributor.committeememberSklan, David S.en
dc.contributor.departmentAnimal Scienceen
dc.date.accessioned2014-03-14T21:12:47Zen
dc.date.adate2008-06-06en
dc.date.available2014-03-14T21:12:47Zen
dc.date.issued1996-11-18en
dc.date.rdate2008-06-06en
dc.date.sdate2008-06-06en
dc.description.abstractThe purpose of this research was to study vitamin A status in grazing horses throughout the year and to evaluate the effectiveness of vitamin A and β-carotene as supplements. Vitamin A status was assessed by serum retinol concentrations (SR) and the relative dose response (RDR) which was adapted for use in the horse. The horses (45 Thoroughbred mares) were divided into three diet groups: pasture and hay only (PH); pasture, hay and vitamin A-free concentrate (PHC); and hay and vitamin A-free concentrate (HC). The mares, as well as their foals, were assessed for vitamin A status during the summer, fall and winter. After eight months, each diet group was subdivided and supplemented with either: retinyl palmitate at two times the recommended level (A), the equivalent in water dispersible β-carotene (B), or a placebo (C). Supplementation continued for 20 months during which the vitamin A status was assessed every 60 days in the mares, and at birth in the neonates. During both the depletion and the repletion phase the mares were kept on a regular breeding schedule and the reproductive rates were determined as well as the general health of the mares and their offspring. The RDR proved more sensitive at detecting changes in vitamin A status than SR, and a combination of both was used. A measurable decline in vitamin A stores was seen in the HC group within 2 months, and in PH and PHC groups during the winter. The HC group remained lower in vitamin A status throughout the study. A seasonal fluctuation of vitamin A status was observed regardless of supplementation. Supplementation with retinyl palmitate improved vitamin A status in all three diet groups, however, supplementation with β-carotene did not. Both neonates and young growing horses were lower in vitamin A status than the adult. A respiratory infection observed in the weanlings affected vitamin A status as well. Supplementation of the dam had no effect on neonatal vitamin A status. Deleterious effects on reproductive rates and health were also observed with vitamin A depletion. Supplementation of β-carotene had a negative effect on reproductive rates in this study.en
dc.description.degreePh. D.en
dc.format.extentx, 159 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-06062008-155702en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-06062008-155702/en
dc.identifier.urihttp://hdl.handle.net/10919/38134en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V856_1996.G745.pdfen
dc.relation.isformatofOCLC# 36391788en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectHorsesen
dc.subjectgrowthen
dc.subjectvitamin Aen
dc.subjectβ-caroteneen
dc.subjectReproductionen
dc.subjectrelative dose responseen
dc.subjectserum retinolen
dc.subject.lccLD5655.V856 1996.G745en
dc.titleVitamin A depletion and repletion in thoroughbred horsesen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineAnimal Scienceen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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