Changes in plasma concentrations of leptin in ewes during pregnancy

Previous research has demonstrated circulating concentrations of leptin increase in ewes during mid pregnancy then decline in late pregnancy and early lactation. The objective of this study was to more narrowly define the timing of changes in circulating concentrations of leptin with pregnancy in ewes. Katahdin ewes (n= 19) located at latitude 34.275 and longitude -85.183 (Mount Berry, GA) were utilized. Blood samples were collected weekly via jugular veinpuncture beginning immediately before ram exposure on September 23 and continuing until 4 weeks post-lambing. Ewes were exposed to a ram fitted with a marking harness for a 63 day breeding season. Breeding marks were recorded daily. Lambing date and number of lambs born was recorded. Week of gestation was calculated by breeding mark. The blood sample collected prior to breeding was considered week 0. Plasma concentration of leptin was determined by radioimmunoassay. Data were tested for effects of date of sample, pregnancy status, and date of sample by pregnancy status interaction using procedures for repeated measures (JMP version 7; SAS Institute Inc., Cary, NC). Data were also tested for effects of week of gestation and number of lambs. Pregnancy had an effect on plasma concentrations of leptin (P = 0.0407; 6.06 ± 0.19 vs 4.67 ± 0.64 ng/ml in pregnant vs non-pregnant ewes, respectively). There was also an effect of date of sample (P < 0.0001) on plasma concentrations of leptin. Week of gestation had an effect of plasma concentrations of leptin (P < 0.0001) with ewes having lower plasma concentrations of leptin during weeks 12, 13, 16, and 18-21 of gestation as well as four weeks after lambing when compared to before breeding. Plasma concentrations of leptin were higher weeks 1-12, 14, 15, and 17 of gestation than after lambing, but did not differ from values before lambing. These data confirm a decline in circulating concentrations of leptin in the last third of gestation and continuing into early lactation in ewes.