Abstract
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.
Highlights
Assisted bovine reproductive techniques have been increasingly used because of the need for reproductive efficiency
The objective of the study was to establish the physiological patterns of serum progesterone concentration in estrous cycle by chemiluminescence in dairy cows
Our results showed P4 concentrations of 5.49 to 28.6 ng/mL for the active corpus luteum (CL), which are much higher than those reported by Fantini Filho et al (2004)
Summary
Assisted bovine reproductive techniques (such as artificial insemination, timed-artificial insemination, embryo transfer, fixed-time embryo transfer, and in vitro embryo production) have been increasingly used because of the need for reproductive efficiency. In order to make the aforementioned biotechnologies more efficient, it is necessary to provide laboratory support, based mainly on hormonal determinations of progesterone (P4). Serum P4 profile can be determined using immunoassays such as radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), fluoroimmunoassay (FIA), or chemiluminescence immunoassay (CLIA). Immunoassays utilize the principle of binding of an antibody to its specific antigen to measure the concentration of either the antigen or the antibody. Any marker that allows sensitive measurements can be used. One of the first markers developed was a radioactive isotope, which resulted in the development of RIA technique that is currently still in use. The measurement depends on the ability of the unlabeled (unknown) antigen to inhibit the binding of the radioactive antigen and the antibody, and it is considered a competitive immunoassay (Parker, 1981)
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