Leptin Levels at Different Stages of the Luteal Phase in Cattle and Their Relationship with Conception

The objective of this study was to evaluate the relationship between plasma leptin levels in the early and late luteal periods of cows and conception rate. In the present study, the ovsynch + progesterone (P4) protocol was employed in 50 Holstein cows. Blood samples were collected on the 5th and 18th days following artificial insemination, and the levels of leptin and progesterone were subsequently measured. Subsequent to artificial insemination, mean leptin levels in the early (day 5) and late (day 18) luteal phases of the cows were measured as 5.96 ± 2.54 and 8.02 ± 4.14 ng/mL, respectively. Levels of leptin in the blood of pregnant cows on both day 5 (9.01 ± 4.40 ng/mL) and day 18 (12.04 ± 6.49 ng/mL) were higher than those in the blood of non-pregnant cows (4.44 ± 3.83 ng/mL and 6.01 ± 4.93 ng/mL, respectively). The findings revealed that progesterone levels on the 5th day following artificial insemination exhibited higher mean values (2.11 ± 0.64 ng/mL) in pregnant cows as compared to non-pregnant cows (1.49 ± 0.51 ng/mL). Furthermore, a higher level of progesterone was observed on day 18 in pregnant cows (8.89 ± 2.01 ng/mL) in comparison to non-pregnant cows (5.22 ± 2.21 ng/mL) (p<0.05). The study revealed that levels of the hormones leptin and progesterone were elevated in pregnant cows during the early and late luteal phase, in comparison to non-pregnant cows. However, no correlation was determined between P4 and leptin. The conclusion drawn was that, while there was a possibility that leptin levels could have an effect on the process of pregnancy and implantation, no relationship was found between progesterone and leptin levels