Abstract
The specific objective was to determine the possible influences of drenching Propylene Glycol (PrGl) at the early postpartum period on circulating levels of progesterone during ovsynch protocol and risk of pregnancy establishment in primiparous Holstein cows. Animals (n=45) were classified into a control group which did not receive any dietary supplementation (n=20) and PrGl group (n=25) where individual cows received once daily 250 mg PrGl drench starting from day of calving till day 30 postpartum. On day 60 postpartum, individual cows of both groups were submitted to ovsynch program and were timely inseminated. Serum samples as well as ovarian examination using ultrasonography were carried out on two occasions, on day seven of ovsynch at PGF2 alpha and at timed artificial insemination (TAI). Serum samples were assayed for progesterone. Results showed that PrGl drenching did not affect daily milk production, BCS of cows at synchronization as well as pregnancy rate after ovsynch (40 vs. 35% in PrGl and control cows, respectively). Regardless of treatment, cows with low progesterone at TAI had higher PR/TAI. When circulating progesterone levels were divided into quartiles, cows within the first quartile at TAI had nearly five folds greater PR/TAI, when compared to those within the forth quartile (70 vs. 14.5%, respectively). Further, treated and control cows had nearly similar size of CL at PGF2 alpha and pre-ovulatory follicle (POF) size at TAI. The size of CL at PGF2 alpha did not vary between pregnant and non-pregnant cows, regardless of treatment, however, pregnant cows had significantly higher POF size (1.580.25 cm) than control cows (1.390.27 cm). In conclusion, drenching of PrGl during the first 30 days postpartum for primiparous dairy cows did not affect their response to ovsynch. In addition, higher sizes of POF as well as lower levels of circulating progesterone at TAI were associated with greater PR/TAI.
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