Rafaela Talini

Determination of progesterone concentration during the estrous cycle in dairy cows using a chemiluminescence assay

The study aimed to determine the patterns of serum progesterone concentration in estrous cycle in dairy cows by a chemiluminescence assay (CLIA). Four non-lactating multiparous Jersey cows were used. Animals with a corpus luteum (CL) in any of the ovaries were induced into estrus. Day zero (d0) of the estrous cycle was defined as the day of visible estrus. Blood samples were collected and ultrasonography (US) of the ovaries were performed until a new manifestation of visible estrus was observed. The lengths of the estrous cycles (estrus to estrus) of the four cows were 20, 21, 22, and 23 days. The mean serum concentrations of P4 (x ± s) were 2.8 ± 1.4 ng/mL in proestrus, 2.4 ± 1.5 ng/mL in estrus, 2.0 ± 1.8 ng/mL in metestrus, and 11.9 ± 5.7 ng/mL in diestrus. The follicular and luteal phases of the estrous cycle were established based on P4 concentrations. P4 serum concentrations ≥5.48 ng/mL indicated the presence of functional CL, which was observed from d3 to d12 of the cycle. P4 concentrations decreased from d13 until next estrus. Thus, the previously mentioned P4 serum concentration was established as the limit for a predominantly functional CL. P4 concentrations < 5.48 ng/mL indicated a nonfunctional CL or CL that is not yet fully formed, which is observed in metestrus. A P4 standard curve, constructed based on the Lorentz distribution, was used to determine values of < 5.48 ng/mL of serum P4 concentration for the follicular phase and ≥ 5.48 ng/mL for the luteal phase. Data obtained from US examinations were consistent with P4 concentrations determined using CLIA. In conclusion, the automated CLIA was efficient in determining the P4 concentrations during the various stages of estrous cycles in dairy cows. The findings of the study will help researchers in the animal reproduction field. We recommend the use of CLIA because it´s available in many laboratories worldwide with the ability to process thousands of samples per day.

Reproductive Performance of Prebubertal and Pubertal Heifers Submitted to Timed Artificial Insemination Protocols

High numbers of prepubertal heifers at the beginning of the breeding season (BS) reduces reproductive efficiency in beef cattle.1 In Brazil, grazing Bos indicus heifers reach puberty between 22 and 36months, and the age at first calving is between 44 and 48months.2 Seasonality, poor pasture management, and poor nutrition during the heifer’s growth phase are some of the variables that lead to the delayed onset of puberty in Bos indicus cattle.3 Studies have been conducted to induce puberty in heifers, using either nutritional management strategies,4 or intravaginal progesterone (P4) devices.5 Sales et al.6 induced prepubertal Bos indicus heifers by administering P4 with estradiol cypionate (ECP) after 10days. Silveira et al.5 used prepubertal and pubertal zebu heifers for timed artificial insemination (TAI). They found a higher pregnancy rate (PR) in the groups that had received P4 with estradiol benzoate (EB) and ECP compared to prepubertal heifers only exposed to bulls. The exposure of prepubertal heifers to P4 for 8days induced and synchronized estrus. Similar effects were observed by Wheaton et al.7 and Demeterco et al.8 Treatment with a P4 intravaginal device induced prepubertal heifers to cycle and also increased the uterine diameter6 even during anestrus.9 The addition of EB at the time of P4 removal potentiates this action.3