Cervical mucus characteristics and periestrual hormone concentration in relation to ovulation time in Zebu (Sahiwal) cattle

The present study was conducted to determine the association among cervical mucus characteristics, periestrual progesterone (P4) and luteinizing hormone (LH) concentrations and ovulation time in Zebu cattle. In experiment 1 the relationship between cervical mucus characteristics and ovulation time was determined. Cervical mucus was collected from Sahiwal cows (n=60) before artificial insemination from mid-cervix and rheological and chemical properties were studied. Ovulation time was determined by ultrasound examination at 2 h intervals starting from the onset of estrus to ovulation. Cervical mucus was copious and thin in 70.2 and 63.2 percent of estrus periods, respectively. Cervical mucus from 57.9 percent of the estruses had a typical arborization pattern. The Means±SEM of pH, electrical conductivity and spinnbarkeit value of the mucus were 7.59±0.06, 15.21±0.15 mS/cm and 11.06±1.06 cm, respectively. Estrus to ovulation duration was significantly greater (P<0.05) in cows that had 8-16 cm spinnbarkeit value of cervical mucus than cows with higher or lower values. In experiment 2 the relationship among peripheral P4, LH concentrations and ovulation time was determined. For this purpose blood samples were collected from 20 Sahiwal cows (10 natural estruses and 10 induced estruses) at 2 h intervals from the onset of estrus until ovulation. Peripheral P4 and LH concentrations were measured using bovine-specific ELISA kits. The duration of estrus to LH-peak and LH-peak to ovulation was 2.2±1.62 h and 29.45±1.73 h in natural estrus and 3.3±0.67 h and 32.75±3.62 h in induced estrus, respectively. The peak LH value did not vary significantly in synchronised (15.26±2.8 ng/mL) and natural estrus (12.67±1.96 ng/mL). Plasma P4 concentration on the day of estrus was significantly greater (P<0.05) in the synchronised estruses (1.23±0.23 ng/mL) compared to the natural estruses (0.65±0.11 ng/mL). The estrus to ovulation interval was significantly (P<0.05) greater when the P4 concentration was >1 ng/mL on the day of estrus (36.17±0.73 h in natural and 37.57±4.32 h in synchronised) compared to <1 ng/mL (31.28±1.74 h in natural and 28.83±3.61 h in synchronised). Taken together, the spinnbarkeit value and arborization pattern of cervical mucus had strong relationship with plasma P4 concentration and ovulation time indicating that the parameters could be used as a tool to decide optimal time of insemination in Sahiwal cattle.