Evaluation of some biochemical factors and conception rates in cows pre-synchronized with progesterone and Presynch before Ovsynch protocolduring postpartum period

The objectives of this study were to investigate the effects of Presynch and progesterone co-administration as a pre-synchronization protocol before Ovsynch on ovarian activity and pregnancy rate in postpartum lactating cows and to evaluate the effects of some hormonal, biochemical and metabolic values on the results obtained during this process. The present study was used as material a total of 160 Simmental breed and crossbred cows aged between 2 and 6 years, which gave birth normally and had no problems in terms of general and reproductive health in the postpartum period. On day 35 of the study, the functional status of the ovaries was examined in all animals via rectal palpation and transrectal ultrasound. In order to ensure homogeneous distribution of the groups, the following factors were taken into consideration: localization status, body condition score, average milk yield and functional status of ovaries, and the animals with similar characteristics were distributed evenly among the groups using a randomization system. The animals were divided into four groups, including a Control (CNT) group that received no treatment and three other groups that received different treatments. The CNT group animals were inseminated approximately 12 hours after the time of first observation of behavioural signs of oestrus, following a voluntary waiting period (postpartum day 49). The Ovsynch (OVS) group animals were subjected to Ovsynch protocol starting from postpartum day 61. Presynch+Ovsynch (PR+OVS) group animals were administered with PGF2α on postpartum day 35. The second injection of PGF2α was administered 14 days later (on day 49) and the Ovsynch protocol was initiated on day12 following this application (on day 61). Presynch/CIDR+Ovsynch (PR/CD+OVS) animals were administered PGF2α on postpartum day 35 and CIDR was inserted 7 days later (on day 42). The second injection of PGF2α was administered 7 days after the application (on day 49) with the removal of the CIDR. The Ovsynch protocol was initiated on day 12 following this application (on day 61). At the end of the Ovsynch protocol, all treatment groups animals were inseminated at the 16th hour following the second GnRH injection (on day 71). At the time of artificial insemination, the clinical and behavioural signs of estrus were observed. Pregnancies were diagnosed between 40-45 days after insemination. The concentration of progesterone, the metabolic profile and the level of oxidative stress were analyzed by taking blood samples from all animals on postpartum day 35 and at the time of artificial insemination. It was determined that 60.0% (96/160) of the animals had non-functional ovaries on the postpartum day 35. Until the postpartum day 70, 65.6% (40/61) of the animals in the CNT group were in heat. This rate was higher in cows with functional ovaries on postpartum day 35. It was observed that the rate of presence of an active corpus luteum on the ovaries of the animals in the treatment groups at the beginning of the Ovsynch protocol was higher in the PR/CD+OVS group (91.7%-22/24) than in the OVS and PR+OVS groups (66.7%-16/24 and 83.3%-20/24, respectively). The behavioral signs of estrus were significantly less observed (p<0.05) in the synchronization groups when compared to the control group during the time of artificial insemination. It was found that the pregnancy rate of animals in the CNT group (70.0-28/40%) was statistically higher (p˂0.05) than the pregnancy rate of animals in the OVS group (45.0-18/40%). In the other hand, an increase was observed in the pregnancy rate of animals in the PR+OVS group (52.5-21/40%) and PR/CD+OVS group (60.0-24/40%) compared to those in the OVS group. This increase was more remarkable in cows with non- functional ovaries on day 35. Although individual differences were observed between the animals in terms of metabolic and oxidative stress parameters, it was determined that the mean values were similar among the groups and these variations had no effects on pregnancy rates. In conclusion, the combined use of Presynch and progesterone before Ovsynch protocol may improve pregnancy rates by increasing the rate of onset of cyclic activity in cows with dysfunctional ovaries on postpartum day 35. Key words: Cow, Presynch, Progesterone, Ovsynch, Pregnancy rate.