Luteinizing hormone response to estradiol benzoate in cows postpartum and cows with ovarian cysts.

Twenty-seven dairy cows were evenly assigned to one of three groups and given an intramuscular injection of 2 mg estradiol benzoate. Cows in group 1 were greater than 30 days postpartum at treatment and had been diagnosed via rectal palpation to have ovarian cysts. Cows in groups 2 and 3 were 12 to 14 and 30 to 40 days postpartum, respectively. Blood plasma was collected from all cows before treatment and then every three hours for 36 hours post-treatment. Concentrations of LH, estradiol-17 beta and progesterone in plasma were determined by radioimmunoassay. Four, zero and five cows in groups 1, 2 and 3, respectively, had concentrations of progesterone greater than 1.0 ng/ml before estradiol benzoate treatment. None of these cows had a peak LH release greater than 5 ng/ml following estradiol benzoate treatment. The numbers of cows with progesterone concentrations less than 1 ng/ml that released LH (>5 ng/ml) in response to estradiol benzoate were 3 of 5, 3 of 9, and 4 of 4 for groups 1, 2, and 3, respectively; the proportion for group 3 was higher (P<.05) than for group 2. Of the cows that released LH, mean peak LH concentrations were 33.3+/-5.4, 14.8+/-7.2 and 24.6+/-9.8 ng/ml for groups 1, 2 and 3, respectively, and the duration of the LH increase was 8.0+/-1.0, 8.0+/-2.0 and 13.0+/-4.0 hours. The time from estradiol benzoate treatment to peak LH release for cows with ovarian cysts (25+/-2 hours) was delayed (P<.05) compared with that for cows 30 to 40 days postpartum without ovarian cysts (16+/-1 hour). In summary, responsiveness to estradiol benzoate is regained between 2 to 4 weeks postpartum in most cows. In addition, some cows with ovarian cysts can release LH in response to estradiol benzoate, but peak LH release is delayed compared to cows at a comparable stage postpartum without ovarian cysts.

GnRH induced LH release in suckled beef cows. 1. The effects of days postpartum and estradiol-17beta concentrations on the release of LH following administration of GnRH.

Twenty suckled CharloixxHereford beef cows (5 cows/group) were assigned at random to receive 100 microg GnRH (IM) at either 2 to 3, 7 to 8, 15 to 16, or 31 to 32 days postpartum, Groups 1 through 4, respectively. Blood samples for hormone determinations were collected at time 0 (pre-GnRH), every half hr for 3 hr, and at 4.0 hr and 6.0 hr post-GnRH. Mean plasma LH, estradiol-17beta, or progesterone concentrations were not different among groups prior to GnRH. Plasma LH increased (P<.05) following GnRH in Groups 2, 3 and 4, but not in Group 1. Peak GnRH induced LH release was greater (P<.05) in Groups 3 and 4 than in Groups 1 or 2. Correlation coefficients between days postpartum and peak LH release (r=.72), and estradiol-17beta concentrations and time of LH peak (r=-.42) were significant (P<.05). These data indicate that LH release in response to GnRH, in suckled beef cows is not fully restored until 15 to 16 days postpartum.

Effect of ovarian activity and endogenous reproductive hormones on GnRH-induced ovarian cycles in postpartum dairy cows.

The objective was to determine the relationship of prior follicular development to GnRH-induced cyclic ovarian activity in dairy cows postpartum. Sixty lactating Holstein and Guernsey cows from the University of Missouri dairy herds were assigned at random to one of two groups. Group I consisted of 20 cows (control) given a single intramuscular (IM) injection of saline. Group II consisted of 40 cows given a single injection of 100 micrograms gonadotropin releasing hormone (GnRH) IM. Treatments were administered 12 to 14 days postpartum. All cows were palpated per rectum to monitor ovarian activity prior to treatment (time 0) and 2 to 3 and 7 to 9 days post-treatment. Blood was collected via tail vessel puncture at time 0 and 7 to 9 days post-treatment. The percentage of cows exhibiting a follicle 10 mm or greater in diameter prior to treatment was not different between Group I (50%) and Group II (43%). However, twenty (50%) of the GnRH-treated cows initiated cyclic ovarian activity following treatment as evidenced by palpable CL and plasma progesterone greater than or equal to 1.0 ng/ml on day 9 post-treatment in contrast to only four (20%) saline-treated cows (P less than 0.05). Seventeen of 20 cows ovulating in Group II exhibited a palpable follicle greater than or equal to 10 mm in diameter prior to treatment compared to 3 of 4 cows in Group I. Prior to treatment, plasma concentrations of LH, estradiol-17 beta and progesterone were not different (P less than .05) between cows in Groups I and II. In Group II, preinjection levels of estradiol-17 beta and LH for cows ovulating in response to GnRH were higher (P less than .01) than in cows not ovulating. Postinjection concentrations of progesterone in plasma on days 7 to 9 were higher (P less than .01) in cows ovulating than in cows not ovulating. Six (30%) cows in Group I developed ovarian cysts prior to conception as compared to 12.5% (5) of the cows in Group II (P less than .05). The present study suggests: (1) GnRH treatment as early as 12 to 14 days postpartum may initiate cyclic ovarian activity in normal dairy cows; (2) elevated preinjection concentrations of estradiol-17 beta and follicular growth are important for GnRH induced ovulations; and (3) GnRH treatment 12 to 14 days postpartum may be useful in reducing abnormal ovarian activity.

Concentrations of progesterone in milk as a monitor of early pregnancy diagnosis in dairy cows.

The objectives of the experiment were to evaluate the efficacy of using progesterone concentrations in milk and palpation per rectum on days 21 or 22 postbreeding to estimate pregnancy and evaluate management practices; and to investigate physiological occurrences leading to incorrect diagnosis of pregnancy when serial samples of milk were collected. Of particular interest were indications of early embyronic death and insemination of cows not in estrus. Milk samples were collected at the afternoon milking of days 0 or 1 (day 0 = day of estrus), 9 or 10, 21 or 22 and 27 or 28 following breeding in 200 lactating dairy cows. Tentative diagnosis of pregnancy was made based on concentrations of progesterone in milk on days 21 and 22 alone and on days 21 or 22 and 27 or 28. In addition all cows were palpated per rectum on days 21 or 22 postbreeding and a tentative pregnancy diagnosis was made. Pregnancy was confirmed by examination of the genital tract per rectum between 35 and 50 days after breeding. Values of 4 ng/ml or greater and/or the presence of a mature corpus luteum were considered positive signs of pregnancy. Progesterone in milk ranged from 0.1 to 18 ng/ml. On days 0 or 1, 9 or 10, 21 or 22 and 27 or 28 concentrations of progesterone in milk averaged 1.5 +/- 0.3, 11.1 +/- 0.5, 12.0 +/- 0.4 12.5 +/- 0.5 ng/ml for pregnant cows. Corresponding samples from nonpregnant cows averaged 1.2 +/- 0.2, 10.3 +/- 0.4, 3.0 +/- 0.4, 6.8 +/- 0.6 ng/ml, respectively. Ninety-six and 104 cows were classified as pregnant and nonpregnant on days 21 or 22 as compared to 78 and 118 cows diagnosed as pregnant and nonpregnant on days 21 or 22 and 27 or 28 combined. Pregnancy detection by progesterone in milk on days 21 or 22 with pregnancy determined via rectal palpation 35 to 50 days postbreeding was 77 and 100% accurate for positive and negative diagnosis, respectively. The percent agreement using progesterone in milk on days 21 or 22 and 27 or 28 combined was 95 and 100%, respectively, for positive and negative diagnosis. Diagnosis based on rectal palpation 21 or 22 days postbreeding was 63 92 (69%) and 76 88 (87%) for pregnant and nonpregnant cows, respectively. Ten of the 200 cows had progesterone concentratins in milk of > 4 ng/ml at the time of breeding. Six of these cows were pregnant from a previous insemination. The other four cows were nonpregnant and were inseminated during the luteal phase of the cycle. In conclusion, measurement of progesterone in milk is a useful tool in early detection of pregnant and nonpregnant cows and may be useful in detecting reproductive problems in a dairy herd. It will probably be most useful when used in combination with later pregnancy diagnosis per rectum .