The objectives were to evaluate the reproductive indices and survival analysis of pregnancy outcomes in multiparous repeat breeder Holstein cows (n = 557). The cows were synchronized to ovulate by Ovsynch, new controlled internal drug release device (N-CIDRsynch), and once-used CIDR device (U-CIDRsynch). The pregnancy per AI at 28 days post-insemination (P/AI 28) in the N-CIDRsynch group (28.75%) was significantly (COR = 1.49; p = 0.011) greater than that reported in the Ovsynch (23.46%) and U-CIDRsynch (21.73%) groups. Furthermore, the pregnancy per AI at day 75 post-insemination (P/AI 75) in the N-CIDRsynch group was significantly greater than the Ovysync group (COR = 1.35; p = 0.050). The repeat breeder cows received a N-CIDR device had a significantly higher progesterone level on day 2 and day 4 of CIDR insertion (1.38 and 1.67 ng/ml, respectively) than those received a U-CIDR device or the control group (p = 0.012 and 0.001, respectively). The Cox regression model recorded significant associations for synchronization protocols, THI at the TAI and season of calving with the hazard of P/AI 28 and P/AI 75 (p = 0.044 and 0.046; 0.001 and 0.005; 0.003 and 0.001, respectively). Multiparous repeat breeder cows (>3) had a lower hazard ratio (HR) of P/AI 28 than that reported in the reference (2nd parity) group (HR = 0.74, p = 0.050). The repeat breeder cows inseminated at 76-80 and >80 temperature-humidity index (THI) had significantly lower HR of P/AI 28 than those inseminated at the baseline (<70) THI value (HR = 0.73 and 0.30, p = 0.036 and 0.001, respectively). The current results indicate that the use of N-CIDR synch protocol may achieve satisfactory pregnancy outcomes in repeat breeder cows.

The aim was to elucidate the impact of oral folic acid (FA) supplements on progesterone profile, blood metabolites and biochemical indices of heat-stressed Holstein cows during the early stage of pregnancy. The study lasted from the day of artificial insemination through the end of the fourth week of pregnancy. The first group (CON, n = 17) received 0 μg of FA/kg BW as a control. The second and third groups received oral FA doses of 5 (FA5, n = 19) and 10 (FA10, n = 20) μg kg−1 BW, respectively. At the 2nd and 3rd weeks of pregnancy, the FA10 group had greater progesterone levels than the CON group (p < 0.05). The FA10 group had a greater progesterone level than the FA5 and CON groups at the fourth week of pregnancy (p < 0.01). The FA10 group had higher folate levels than CON group during the first three weeks of pregnancy (p < 0.01). Both FA-supplemented groups had significantly greater serum folates than the CON group by the end of the fourth week of pregnancy (p < 0.01). At the 2nd and 4th weeks of pregnancy, the FA10 group had greater levels of serum glucose and globulin than the CON group (p = 0.028 and 0.049, respectively). Both FA-supplemented groups had greater serum growth hormone (GH) levels at the 4th week of pregnancy (p = 0.020). Additionally, the FA10 group showed significantly higher levels of IGF-1 at the 2nd and 4th week of gestation (p = 0.040 and 0.001, respectively). FA supplementation decreased the levels of non-esterified fatty acid (NEFA) at the 2nd and 4th week of gestation (p = 0.020 and 0.035, respectively). Additionally, the FA10 group showed significantly higher pregnancy-associated glycoprotein (PAG) levels at the 2nd and 4th week of gestation (p = 0.005 and 0.001, respectively). In conclusion, oral FA supplementation (10 mcg kg−1) in the first month of gestation improved the progesterone profile, as well as blood folates, PAG, GH, and IGF-1 concentrations in heat-stressed Holstein cows. These findings could be useful in developing practical strategies to keep dairy cows’ regular reproductive patterns under heat stress conditions.

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