Long Term and Short Term Changes in Leptin, Insulin and Glucose in Grazing Thoroughbred Mares

The objective was to evaluate the insulin-leptin interactions in grazing mares and their impact on aspects of reproductive function using a series of four studies. Fourteen mares were first examined, 10 grazing and 4 confined to stalls in four 22-h studies in April, August, October (2005) and January (2006). There was a positive relationship between insulin and leptin concentrations (r = 0.50; P < 0.001). The second study used 24 mares maintained at pasture and fed supplements rich in either FF, or SS, or pasture forage. Nonstructural carbohydrate (NSC) content of forage was correlated to insulin concentration (r = 0.55; P < 0.01). Insulin was associated with leptin (r = 0.55; P < 0.001) and progesterone (r = 0.48; P < 0.001). In the third study nine mares adapted to FF, SS or forage only underwent two FSIGT tests; once during the luteal phase and again during the follicular phase of the estrous cycle. Minimal model analysis was used to describe insulin sensitivity (SI), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and the disposition index (DI). SI was lower (P < 0.001) in the luteal phase (3.1 ± 0.6) compared to the follicular phase (5.0 ± 0.6). In the fourth study 15 mares had their follicular fluid collected during the luteal and follicular phase of the estrous cycle. Insulin concentration (ln (x+1)) was 52% higher (P < 0.01) in large (> 25 mm) follicles (1.4 ± 0.1 mIU/L) than either medium (16 to 25 mm) or small (le; 15 mm) follicles (0.9 ± 0.1; 0.9 ± 0.1 mIU/L, respectively) irrespective of estrous cycle phase. A correlation was observed between follicular fluid (FFL) leptin and plasma leptin (r = 0.30; P < 0.001). A similar relationship was observed between FFL insulin and plasma insulin (r = 0.25; P < 0.001). Plasma insulin and leptin were positively associated (r = 0.45, P < 0.0001), along with FFL insulin and FFL leptin (r = 0.46, P < 0.0001). Both leptin and insulin were affected by season and this observation contradicts the use of single sample analysis for determining detrimental concentrations of these hormones.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Animal and Poultry Sciences

Department dc:contributor.department

Animal and Poultry Sciences

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2007

Author dc:creator

• Cubitt, Tania Anne

Chair dc:contributor.committeechair

• Geor, Raymond J.

Committee members dc:contributor.committeemember

• Staniar, William Burton
• Gwazdauskas, Francis C.
• Splan, Rebecca K.
• Bowen, John M.
• Kronfeld, David S.

• leptin
• glucose
• insulin
• estrous cycle
• follicle
• season
• circadian pattern

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-11302007-115548

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/29807