Association of concentrations of beta-carotene in plasma on pregnancy per artificial insemination and pregnancy loss in lactatingHolstein cows.
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The objective of this study was to determine the association of beta-carotene concentration in plasma at the moment of artificial insemination (AI) on pregnancy/AI in lactating Holstein cows. A total of 399 events from 364 lactating Holstein cows were enrolled in the trial (143 primiparous and 221 multiparous). All cows were assigned to a timed AI protocol based on estradiol and progesterone. Blood samples were collected at the moment of AI and at 24 and 31d post-AI (samples on 31d post-AI were collected only from cows that were diagnosed pregnant). The BCS were recorded at the time of AI. Plasma beta-carotene was quantified from blood samples taken at the time of AI using a single step denaturation and extraction into a solvent, followed by measurement using a portable spectrophotometer. Pregnancy-associated glycoproteins (PAG) were analyzed in blood samples taken at 24 and 31d post-AI of pregnant cows. Milk production was collected for the entire experimental period. Pregnancy diagnosis was performed by ultrasound 31 and 60d post-AI. Data was analyzed using the MIXED and GLIMMIX procedures of SAS. Cows classified as thin (<2.75) tended to have lower concentration of beta-carotene at AI when compared with those classified as Moderate (3.00; 3.80.1 vs. 4.30.1g/mL; P=0.09). Concentration of beta-carotene were greater in multiparous compared with primiparous (P<0.01). There was no correlation between concentration of beta-carotene and milk production (r=0.04; P=0.10). When plasma beta-carotene was categorized in quartiles, cows in the 1st quartile had lower pregnancy/AI and higher pregnancy losses when compared with cows that were in the 2nd, 3rd and 4th quartile (pregnancy/AI=19.24.5, 33.74.7, 36.95.0 and 39.85.4%, respectively; P=0.05; pregnancy losses=41.94.8, 20.43.7, 22.14.1, and 15.74.2%, respectively; P<0.05). There was no association between concentrations of beta-carotene at AI and PAG at 24d post-AI (P=0.60). Cows with greater concentrations of beta-carotene at AI were more likely to have greater concentrations of PAG at 31d post-AI (P<0.01). In conclusion, the concentration of beta-carotene at AI was affected by BCS and parity. Cows with higher concentrations of plasma beta-carotene at AI had greater pregnancy/AI, lower pregnancy losses and greater concentrations of PAG at d 31 post-AI, suggesting it may be associated with placental function in lactating dairy cows.