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  • Title: Characteristics and retention of luteal structures, extended postinsemination cycle, progesterone, and pregnancy-specific protein B in serum after human chorionic gonadotropin treatment of dairy cows.
    Author: Stevenson JS, Pulley SL.
    Journal: J Dairy Sci; 2012 Aug; 95(8):4396-409. PubMed ID: 22818453.
    Abstract:
    Our objectives were to determine characteristics (size, number, and stayability) of luteal structures formed in response to human chorionic gonadotropin (hCG) administered on d 7 after timed artificial insemination (AI) and the influence of hCG on returns to estrus and pregnancy outcome. Holstein cows (n=328), milked 3 times daily, previously inseminated at first service were assigned randomly to a completely randomized design consisting of 2 treatments when at least 1 corpus luteum (CL) was detected on d 7 after AI. Treatment consisted of 1,000 IU hCG or 1 mL of saline (control) administered i.m. Blood was collected and luteal structures were mapped and sized by transrectal ultrasonography on d 7, 14, 21, 28, and 32 after AI. Blood also was collected on d 60 in all pregnant cows. Treatment with hCG induced new luteal structures in 70% of cows, regardless of pregnancy status or number of pretreatment CL. Cows producing greater than the median 46 kg of energy-corrected milk per day were less likely to respond to hCG. The number of total luteal structures per cow, original CL volume, and total luteal volume (original CL + new luteal structures) were increased by hCG. Progesterone concentration was greater in pregnant than nonpregnant cows on d 14 unless cows responded to hCG by forming new luteal structures. Concentrations of progesterone were greatest in pregnant, hCG-treated cows. Pregnancy per AI at d 32 or 60 after first AI was less in hCG- than saline-treated cows because pregnancy outcome for hCG cows that had only 1 pretreatment CL and failed to respond to hCG was only 55 to 61% of that observed in controls. Proportions of cows returning to estrus from 18 to 25 d after AI were less in hCG than control cows but greater for cows returning >25 d. Regardless of treatment, 25% of cows in both treatments retained at least 1 original CL to d 28 after AI and were not pregnant on d 32. Progesterone concentrations in these nonpregnant cows with retained CL between d 14 and 28 after AI were intermediate between nonpregnant cows that returned to estrus by d 25 and all pregnant cows. Concentrations of pregnancy-specific protein B were elevated in some of these nonpregnant, CL-retained cows, indicating early pregnancy loss. Retention of original luteal tissue in nonpregnant cows to d 28 after AI indicated that pregnancy had been initiated but failed, as verified by concentrations of progesterone and pregnancy-specific protein B.
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