فهرست مطالب mohammad ali eslami

The past few decades have seen a dramatic decrease in the fertility of dairy cows. Thus, reproductive performance became one of the main concerns in the dairy cow industry. Improvement of fertility increases the farmer’s income by reducing the culling rate, increasing milk production, and reducing the calving interval. Factors involved in reproductive management are multifactorial such as management, nutrition, and genetics. Synchronization protocols are one of the main management tools that have improved the reproduction of high-producing dairy cows. Nevertheless, the efficiency of these protocols is still not satisfying and the current study was carried out to improve the double Ovsynch protocol in postpartum dairy cows.

A total of 318 healthy postpartum dairy cows were used in the current study. Data of parity and milk yield (1st and 2nd months) were recorded for all cows. Briefly, on 40 DIM, cows were subjected to a double Ovsynch program and were checked for corpus luteum via ultrasonography on d 57, at the start of the 2nd Ovsynch. Cows without CL were divided into two groups including control (DO-CL, continuing the routine program), and DO+CIDR (including one progesterone supplement). Those bearing CL were considered as DO-CL receiving routine injections. All cows were checked for pregnancy via ultrasonography on d 32, 60, and 120 post-AI, and pregnancy per artificial insemination (P/AI) and pregnancy loss rate were calculated. Data were analyzed using the GLIMMIX Procedure of SAS software.

Cows bearing CL at the start of TAI Ovsynch, compared to DO-CL and DO-CIDR groups, had significantly higher P/AI on d 32 (50.84 vs. 29.27 and 41.46%, P = 0.03), 60 (45.76 vs. 21.95 and 36.58%, P = 0.01), and 120 (43.22 vs. 21.95 and 34.14%, P = 0.03) post-AI. Although cows with CL at the start of the TAI program had 15% lower pregnancy loss compared to the control group, this trait in the 2nd (P = 0.31) and 3rd-4th month (P = 0.75) was not significantly affected by treatments. Parity (primiparous vs. multiparous) had a significant effect on P/AI on d 32 (P = 0.04), but not on d 60 (P = 0.17) and 120 (P = 0.28) post-AI. The effect of milk yield (M ≥ 36 vs. M ˂36) on P/AI at d 32 (P = 0.003), 60 (P = 0.001), and 120 (P = 0.001) was significant. Dairy cows in M ˂36 group compared to M ≥ 36 had significantly higher P/AI on d 32 (52.96 vs. 35.63%), 60 (46.62 vs 28.11%), and 120 (44.41 vs. 26.08%) post-AI. The effects of treatment × parity (P = 0.41) or treatment × milk yield (P = 0.45) interactions were not significant.

Improvement of P/AI via evaluating the presence of CL at the start of the TAI program and using a progesterone insert in cows without CL suggests an important role of progesterone during the growth of ovulatory follicles. Therefore, the identification of cows not bearing CL and applying progesterone is highly recommended. However, the difference between P/AI in cows that received CIDR compared to those in diestrous suggests that using a CIDR may not be sufficient and two CIDRs should be applied in order to achieve optimum results.