Randel Rd

Profiles of reproductive hormones associated with fertile and nonfertile inseminations of dairy cows

Differences in plasma levels of estrogen, progesterone, luteinizing hormone (LH), and urinary estrogens between fertile and nonfertile matings in dairy cows were studied. Samples were collected at 8-hour intervals prior to ovulation (Day 0), every day through Day 8, and on alternate days during Days 10-18. Every nonfertile case had hormonal levels outside the limits found in 10 of 11 fertile cases. Of 27 cases, 30 which involved lactating cows, 32 had a palpable corpus luteum following insemination, and 11 were fertile. Delayed estrus and a delayed preovulatory increase in LH following a decrease in progesterone to less than .75 ng/ml were consistently observed in nonfertile matings. These cases represented 75% of those with subnormal postovulatory levels of progesterone. Asynchronies among nonfertile cases compared with fertile cases involved progesterone, LH, estrogens, and urinary estradiol-17beta prior to ovulation. Examples illustrative of abnormal hormonal profiles included ovarian cysts and early and late regression of the corpus luteum.

Dietary urea for dairy cattle IV. effect on reproductive hormones

Abstract Effects of continuous free-choice feeding of urea in blended rations on reproductive hormones were compared during three consecutive reproductive periods. Urea nitrogen replaced plant nitrogen as follows for Groups 1, 2 and 3, respectively: 0, 22 and 45% from insemination to mid pregnancy, 0, 8 and 16% thereafter until 2 weeks before first calving, and 0, 18 and 36% precalving and during lactations. Dietary urea was consistently associated with significantly increased progesterone in blood plasma at all periods. In contrast, estrogen was significantly lower in urine of Group 3 during Days 1 to 18 after first insemination as heifers, but not at second calving or during Days 1 to 18 after insemination for third pregnancy. Plasma estrogen was significantly lower in Group 3 than Group 1 only during the first pregnancy. Group 2 was intermediate. Length of first gestation was subnormal in Groups 1 and 2. It was concluded that dietary urea caused differences in reproductive hormones which were improtant only during the first pregnancy as heifers.