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Concentrations of progesterone, estrogen, and insulin in serum during early pregnancy in crossbred Angus beef heifersConcentrations of progesterone, estrogen, and insulin in serum during early pregnancy in crossbred Angus beef heifers
Objectives were to evaluate circulating progesterone, estrogen, and insulin concentrations in beef heifers during the first 50 d of gestation. We hypothesized that concentrations of progesterone would remain constant during pregnancy while estrogen and insulin would fluctuate during the establishment of pregnancy. To address our hypothesis, crossbred Angus heifers (n = 46), were synchronized, bred via AI and fed to gain 0.22 kg/ d. Blood samples were taken via jugular venipuncture on d 16, 22, 28, 34, 40, and 50 of gestation. Non-bred, non-pregnant control heifers were sampled on d 16 of the estrous cycle. Concentrations of progesterone, estrogen, and insulin in serum were determined using an Immulite 1000 (Siemens, Los Angeles, CA). Statistical analyses were done within PROC MIXED of SAS with day as the variable and cow as a repeated measure. Progesterone was analyzed with a Compound Symmetry covariance structure. Estrogen and insulin were analyzed with a Toeplitz covariance structure. Concentrations of progesterone on d 0 and 50 (1.8 ± 1.8 and 3.6 ± 1.0 ng/mL; respectively) were decreased (P < 0.01) compared with all other days (7.4 ± 0.6 ng/mL). Concentrations of estrogen were similar (P > 0.40) among non-pregnant (42.4 ± 9.0 pg/mL) and pregnant heifers (44.2 ± 3.1 pg/mL). Pregnant heifers had decreased (P < 0.05) concentrations of estrogen on d 16 (36.5 ± 2.5 pg/mL) compared with all other days (45.7 ± 3.2 pg/mL). Concentrations of estrogen were greater (P < 0.05) on d 40 (50.5 ± 3.6 pg/mL), compared with d 28 and 50 (42.7 ± 2.7 and 43.9 ± 3.9 pg/mL; respectively). Concentrations of estrogen tended (P = 0.07) to be decreased on d 22 vs. d 40 (44.4 ± 2.7 vs. 50.5 ± 3.6 pg/mL; respectively). There was also a tendency (P = 0.08) for estrogen to be reduced on d 28 (42.7 ± 2.7 pg/mL) compared with d 50 (43.9 ± 3.9 pg/mL). Concentrations of insulin were not different (P = 0.53) among pregnancy status or days of gestation. In conclusion, concentrations of progesterone in non-pregnant heifers were less than those of pregnant heifers until d 50 post-breeding, and estrogen but not insulin was differentially observed through the early gestational period.
Keywords:
beef cattle, early gestation, estrogen, progesterone