Hirokazu  Kubota, Toshihiko  Nakao, Abdelrahim  Hommeida, 
    Reduced Pregnancy Rates in Lactating Cows Inseminated Following Short or Prolonged Luteal Phases,
    Journal of Animal and Veterinary Advances,
    Volume 10,Issue 16,
    2011,
    Pages 2167-2171,
    ISSN 1680-5593,
    javaa.2011.2167.2171,
    (https://makhillpublications.co/view-article.php?doi=javaa.2011.2167.2171)
    Abstract: The objectives of this study were to describe the luteal phase during the estrous cycle preceding first insemination (1st AI) and to assess its association with the pregnancy rate. From forty-one cows milk samples were collected three times a week starting 2nd week postpartum until cows returned to estrus or were diagnosed pregnant after 1st AI. Progesterone concentrations in defatted milk were measured by enzyme immunoassay. Based on the duration of the luteal phase in the cycle preceding 1st AI, 27 (65.9%) cows had normal luteal phase (12-19 days), 8 (19.5%) had prolonged (&ge;20 days; PLP), 5 (12.2%) had short (&lt;12 days; SLP) and in one cow there was no luteal phase. Peak progesterone values were lower in cows with SLP than in cows with PLP or normal luteal phase (1.50, 2.27, 2.20 ng mL<SUP>-1</SUP>, respectively p&lt;0.01). About 5 (62.5%) of the eight cows with PLP in the preceding cycle repeated the PLP in the cycle subsequent to 1st AI. Of the 15 cows not conceiving to the 1st AI, 10 (66.7%) had abnormal luteal phases (SLP, PLP and absent) while only 4 (15.4%) of 26 cows which conceived had abnormal luteal phases (p&lt;0.01). The incidence of abnormal phases increased in cows in third parity than first or second parity (p&lt;0.05). In conclusion, inseminating cows after short or prolonged luteal phase was associated with reduced pregnancy rate.
    Keywords: cycle;pregnancy rate;luteal phase;Dairy cow;Japan;insemination