This study was carried out to examine the relationship between the corpus luteum (CL) weight, CL and follicle diameters and progesterone, beta-carotene and vitamin A levels in reproductive organs of cattle obtained from the slaughterhouse. The beta-carotene and vitamin A levels were determined in plasma, CL and follicular fluid (FF) using a spectrophotometric method at different stages of the oestrous cycle (n=40) and at 3-6 months of pregnancy (n=10). The diameters of the CL and follicle were measured using ultrasonography. Plasma progesterone concentrations were determined by an enzyme immunoassay method. The vitamin A levels of the plasma, CL and FF were not related to each other. The highest plasma vitamin A levels were observed in the proestrus and oestrus, at which periods follicular activity dominates. The vitamin A levels in the CL and FF were negatively related to the weight and diameter of the CL and the diameter of follicle, respectively. In contrast to vitamin A, beta-carotene concentrations of plasma, CL and FF were significantly correlated with each other. The highest beta-carotene levels in the plasma, CL and FF were found during pregnancy when there is maximal luteal function, and the beta-carotene level of the CL was significantly correlated with the weight and diameter of CL. Furthermore, the intrafollicular beta-carotene level was negatively correlated with the follicle diameter. There was a positive correlation between plasma progesterone level and the weight and diameter of the CL, but a negative correlation between plasma progesterone level and follicle diameter. Moreover, plasma, FF and CL beta-carotene levels were positively correlated with plasma progesterone levels. This study revealed that beta-carotene levels in the plasma, CL and FF were influenced by the stage of the oestrous cycle or the pregnancy and were related to bovine luteal function without depending on vitamin A.

We previously reported that administration of flunixin meglumine two times at a critical stage approaching pregnancy recognition associated with maintenance of the corpus luteum (CL) increased early embryo survival and pregnancy rate via an additive antiluteolytic effect with the conceptus [Vet Rec 160 (2007) 404]. In this study, the objective was to determine if a single administration of meloxicam, a non-steroid anti-inflammatory drug with a longer half-life, could be used instead of flunixin meglumine. This would avoid repeated injections in heifers following insemination at a critical stage to increase pregnancy rate due to its inhibitory effect on prostaglandin F(2alpha) synthesis. Eighty-five, 15- to 18-month-old Holstein heifers were synchronized, and following insemination (day 0) heifers were assigned to receive subcutaneous meloxicam injection (0.5 mg/kg; n = 37) on the afternoon of day 15 or were untreated as a control (n = 48). Pregnancy rates were defined as the percentage of heifers inseminated that were diagnosed pregnant by ultrasound between days 31 and 38 after artificial insemination. Effect of the treatment on pregnancy rates was analysed by chi-square test. Meloxicam treatment on day 15 after insemination dramatically decreased pregnancy rates in the heifers (52%; 25 of 48 in the control group vs 24.3%; 9 of 37 in the meloxicam-treated group; p < 0.01). This result indicates that administration of meloxicam at the time associated with pregnancy recognition processes to maintain the CL was harmful to the pregnancy even though the drug is considered to be safe during pregnancy in cattle.

Fifty-two 15-month-old Holstein heifers were synchronised with single or double injections of prostaglandin F(2alpha), followed by an injection of gonadotrophin-releasing hormone (gnrh) 48 hours later, and inseminated 12 to 14 hours after the injection of gnrh (day 0). Half of them were then injected twice intramuscularly with 1.1 mg/kg flunixin meglumine 12 hours apart, on the evening of day 15 and the morning of day 16, and the other 26 were not treated. Pregnancy was diagnosed by ultrasound 29 and 65 days after they were inseminated. On day 29, 20 of the treated heifers were pregnant compared with 13 of the control heifers (P<0.05); on day 65, 18 of the treated heifers were still pregnant compared with 12 of the control heifers (P<0.10).

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