Hormonal and Reproductive Profiles of Early Postpartum Beef Heifers after Prolactin Suppression or Steroid-Induced Luteal Function3

Abstract

Two trials were conducted with 24 primiparous suckled beef heifers to determine independent and combined effects of a prolactin-suppressing agent and exogenous steroids on serum hormones and reproductive activity. Heifers were assigned in groups of six to one of four treatments: 1. (C)-subcutaneous control injections administered once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpartum or until first naturally occurring estrus; 2. (CB)-subcutaneous injections of 80 mg CB-154 (2-bromo-~-ergokryptine) (Sandoz) in ethanol once a day for 2 days, followed by 2 days of no injections; sequence repeated from day 5 through day 40 postpartum or until first naturally occurring estrus; 3. (PE)-intramuscular (IM) injection of 25 mg progesterone in sesame oil on day 15 postpartum, followed by IM injection of 4 mg estradiol-17 in sesame oil 48 hr later, or 4. (CBPE)-treatments 2 (CB) plus 3 (PE). A marked reduction in serum prolactin was observed after a single injection CB-154 in all CB and CBPE treated heifers, reaching minimum concentrations by day 7 postpartum after a second injection on day 6. Continued treatment decreased (P<.01) prolactin concentrations over the 35 day blood sampling period to an average of .9 + .2 ng/ml as compared to 19.2 + 5.6 ng/ml for non-CB-154 treated (C and PE) heifers. In non-CB-154treated heifers, serum prolactin was higher during the spring (33.5 -+ .9 ng/ml) than the fall (2.6 + .9 ng/ml). Treatment CB had no effect on serum concentrations of LH, estradiol-17/3 or progesterone. The resumption of cyclic activity in C and CB heifers prior to day 40 postpartum was characterized in four of six animals by 4-to 5-day elevations of serum progesterone and 7-to 8-day cycles, which were preceded in every case by peaks of estradiol-17/3 (9 + 1.9 pg/ml) and nonstanding estrous behavior (three of four) or no behavior (one of four). Palpable corpora lutea were detected in two of four animals during these progesterone increases. Subnormal luteal function was followed by another estradiol-i7/3 peak (7 ---2 pg/ml) and estrus (three of four) or nonstanding estrus (one of four). Injection of progesterone followed by injection of estradiol-17/3 resulted in a preovulatory discharge of LH in 12 of 12 PE and CBPE heifers, with eight of 12 initiating luteal function within 72 hr after the LH surge. On the basis of endocrine data, suppression of endogenous prolactin release did not (P<.05) potentiate steroid treatment effects. Treatments PE and CBPE resulted in a reproductive trend which reflected endocrine findings. Data fail to provide evidence that prolactin is antigonadotropic in bovine heifers. (

Modulation of reproductive hormones by suckling and exogenous gonadal hormones in young beef cows post partum

“…However, the effect of reducing hyperprolactinaemia with bromocriptine did not shorten the anoestrous period in beef cows (Williams & Ray, 1980) and Webb, Lamming, Haynes & Foxcroft (1980) The transient elevation (> 1-5-2 ng/ml) in plasma progesterone which lasts 3-5 days and precedes the first oestrus has been reported previously (Pope, Gupta & Munro, 1969;Webb et ai, 1980). Such transient peaks in plasma progesterone occurred in 4 of the non-suckling cows (Numbers 7, 9, 10 and 11) but did not occur in the suckling cows.…”

A review of female cattle reproduction with special reference to a comparison between buffaloes, cows and zebu

“…The differences in concentration may relate to assay methodology, or to climate because daylength and ambient temperature are important in regulating prolactin release (Koprowski & Tucker, 1973). High prolactin concentrations, however, are not thought to be antigonadotrophic (Williams & Ray, 1980) or to be the cause of prolonged post-partum anoestrus in cows (Webb et al, 1980).…”

Endocrine regulation of postpartum ovarian activity in cattle : a review

“…Moreover, anoestrus length was observed by some (Chang et al, 1981) but not others (Webb et al, 1980) to be closely correlated with plasma prolactin concentrations. Finally, the injection of prolactin (Forrest et al, 1980) or of bromocryptin (Williams and Ray, 1980), an inhibitor of prolactin release, influences neither the variations of LH or FSH concentrations nor the resumption of cyclic activity after calving delay at least in bovines. However, we cannot rule out an ovarian local effect of this hormone on the synthesis of progesterone (Mc Natty et al, 1976, 1977 and on follicular development (Tsai-Morris et a/., 1983).…”