Relationship of pregnancy rate to peripheral concentrations of progesterone and estradiol in beef cows.
The relationship between pregnancy rate and concentrations of progesterone (P(4)) and estradiol-17beta (E(2)) in serum was examined in inseminated beef cows. Jugular blood was collected twice daily on Days 4 through 7 and Days 14 through 17 after estrus to establish patterns of secretion of P(4) and E(2). Pregnancy rate was determined by palpation per rectum at 45 d. Mean concentrations of each hormone, ratio of E(2):P(4) and regressions of hormone on day were the variables measured for each of the 2 periods. Cows were classified into low (n=26), medium (n=50) and high (n=26) groups for each variable. The relationship of pregnancy rate to each variable was tested using Chi-square analyses. Pregnancy rates to the first service decreased linearly as relative mean concentrations of E(2) increased on Days 14 through 17 (P<0.05) but were not affected by any of the other hormonal variables studied during either period. Pregnancy rates to the second service were not related to concentrations of P(4) or E(2) during the luteal phase before mating (Days 14 through 17). The effects of pregnancy on concentrations of E(2) and P(4) also were tested. On Days 14 through 17, P(4) increased slightly in pregnant cows and declined slightly in nonpregnant cows (P<0.05), but pregnancy did not affect E(2) during either period or P(4) on Days 4 through 7. In summary, pregnancy rate to the first service decreased significantly as concentrations of E(2) increased on Days 14 through 17.
Pritchard
J Y
JY
Division of Animal and Veterinary Sciences West Virgina University Morgantown, WV 26506, USA.
Schrick
F N
FN
Inskeep
E K
EK