The postpartum induced corpus luteum: functional differences from that of cycling cows and the effects of progesterone pretreatment

Body condition at parturition and postpartum weight changes do not influence the incidence of short-lived corpora lutea in postpartum beef cows1

Seventy-seven multiparous beef cows (Hereford and Angus x Hereford) with thin to moderate BCS at calving were used to evaluate the effects of body condition at parturition and BW change after calving on duration and occurence of luteal activity before and after first estrus. Blood samples were collected twice weekly after parturition to determine the occurrence of the first postpartum luteal activity (LA, progesterone > or = 0.5 ng/mL). Weight changes and BCS were determined at 2-wk intervals. Cows were exposed to bulls and observed twice daily for behavioral estrus. Luteal activity was classified as normal if plasma concentrations of progesterone were > or = 0.5 ng/mL for at least 11 d, or short if concentrations of progesterone were > or = 0.5 ng/mL for 10 d or less. The interval from parturition to first normal LA was shorter (P < 0.001) for moderate condition (BCS > or = 4.5) than for thin (BCS < or = 4) cows (58.3 +/- 3.2 vs. 93.3 +/- 5.1 d, respectively). Interval to first estrus also was shorter (P < 0.001) for moderate than for thin cows (53.3 +/- 3.7 vs. 89.3 +/- 5.6 d, respectively). Before the first normal LA, 78% of cows had an increase in progesterone for < 11 d. Postpartum weight change and BCS at calving did not influence the incidence of estrus associated with first normal LA. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase, and 12% lacked LA. Postpartum weight change and BCS did not influence the length of LA associated with the first estrus. Cows with normal LA had increased (P < 0.05) maximal concentrations of progesterone compared with cows that had a short luteal phase. When a transient increase in progesterone occurred before first behavioral estrus, 81% of cows had normal luteal function after estrus. We conclude that when beef cows are in thin to moderate body condition at calving, postpartum BW change and BCS at calving do not influence the duration of luteal activity before or after the first postpartum estrus.

Postpartum acyclicity in suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows is a source of economic loss to beef cattle producers. Duration of postpartum acyclicity is influenced by suckling status, nutritional status, calving season, age, and several other factors. Although uterine involution begins and ovarian follicular waves resume soon after parturition, dominant follicles of these waves fail to ovulate, due to a failure to undergo terminal maturation. As a result, postpartum anovulatory dominant follicles are smaller than the ovulatory follicles in cyclic cows. Failure of postpartum dominant follicles to undergo terminal maturation is due to absence of appropriate LH pulses, a prerequisite for follicular terminal maturation prior to ovulation. Absence of LH pulses early post partum is primarily due to depletion of anterior pituitary LH stores, although GnRH pulses are also absent during this period due to suckling. Following replenishment of LH stores between Days 15 and 30 post partum, absence of LH pulses is due to continued sensitivity of the hypothalamic GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta, which results in absence of GnRH pulses. This negative feedback effect of estradiol-17beta is modulated by suckling which stimulates release of endogenous opioid peptides from the hypothalamus. As the postpartum interval increases, sensitivity of the GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta decreases. This is followed by an increasing frequency of GnRH discharges and LH pulses, terminal follicular maturation, ovulation, and continued cyclicity. The first ovulation post partum is usually followed by a short cycle due to premature luteolysis because of premature release of PGF2alpha from the uterine endometrium, which is possibly intensified by the suckling-induced oxytocin release from the posterior pituitary. A model for the postpartum ovulatory acyclicity and for the resumption of cyclicity is presented.

Pharmacologic manipulation of fertility

The professional application of agents to the manipulation of fertility of cows requires basic and applied knowledge of the physiologic mechanisms that are affected and of the pharmacologic agents that are used. In all areas of the pharmacologic manipulation of fertility, the achievement is less than the ideal, and further research is required to improve the efficiency of treatments. The induction of estrus in acyclic animals can involve a reduction in the depth of anestrus, pretreatment with progestagen to ensure estrous behavior and the formation of a normal corpus luteum, and then treatment with exogenous gonadotropin. Responsiveness to treatment can be variable and reflects the depth of anestrus of the animals. Improved treatment regimens require a knowledge of the basic mechanisms involved with the depth of anestrus, a means of assessing the depth of anestrus, and an understanding of the hormonal requirements of ovarian follicles for development and maturation in animals at different depths of anestrus. The optimal precision in the synchronization of estrus (and ovulation) in cyclic animals requires the synchronization of both follicular waves and the end of progestational phase. The end of progestational phase can be synchronized effectively using prostaglandin F2a (or analogs), or by treatment with progestagens with or without luteolytic agents. Procedures to synchronize follicular waves need to be established. The induction of superovulation can be achieved readily using gonadotropins prior to estrus synchronization using prostaglandin F2a. The responses to standard treatments in terms of ovulation rates and yield of transferable embryos are highly variable. The development of procedures to reduce this variability requires an understanding of the intra-ovarian mechanisms involved in recruitment of follicles for a wave of follicular growth, in the selection of dominant follicles for further development, and in the mechanisms controlling follicular atresia. Cystic ovarian disease can be treated effectively using HCG or GnRH (follicular cysts) or prostaglandin F2a (luteal cysts). The basic mechanisms resulting in failure of estrogen positive feedback on LH secretion (that results in cystic follicles) remain to be determined. Small but significant increases in pregnancy rates can be achieved treating cows with prostaglandin during the post-partum period, with prostaglandin to induce estrus for insemination, with GnRH or HCG at estrus, and with GnRH or progestagen treatment during diestrus. Beneficial effects of treatment have been shown in some trials but not in others.(ABSTRACT TRUNCATED AT 400 WORDS)

First postpartum luteal function in dairy cows after ovulation induced by progestogen and gonadotropin-releasing hormone

The objective was to determine the effects of progestogen treatment on the lifespan of the first corpus luteum induced by GnRH in periparturient-milked cows. Dairy cows (n = 55) were assigned randomly following normal parturitions to receive either a progestogen implant (6 mg of norgestomet) or a blank implant (control) for 6 d beginning 2 to 5 d after calving. Fifty micrograms of GnRH were administered i.m. 72 h after implant removal to induce ovulation. Concentrations of LH and FSH in serum from 24 to 30 h and from 66 to 72 h after implant removal were similar among treatments. The magnitude of LH released after GnRH injection was higher in progestogen-treated cows (7.6 +/- .9 ng/ml) than in controls (5.3 +/- .9 ng/ml). Concentrations of estradiol in serum from the beginning of the implant period until 3 d after GnRH injection were higher in cows receiving progestogen (9.1 +/- 1.7 pg/ml) than in controls (5.6 +/- 1.7 pg/ml). The proportion of cows that responded to GnRH (elevated concentrations of progesterone in serum greater than .5 ng/ml within 3 to 5 d after injection) tended to be higher in cows receiving progestogen (24 of 28) than in control cows (19 of 27). By definition, interval to first ovulation after GnRH injection was shorter in cows responding to GnRH (3.8 +/- .5 d) than in those failing to respond (20.2 +/- .9 d).(ABSTRACT TRUNCATED AT 250 WORDS)

Superovulation of beef heifers with Folltropin: A new FSH preparation containing reduced LH activity

The optimum superovulatory dose of Folltropin was determined and compared with a standard 28 mg dose of FSH-P in beef heifers. In Experiment 1, mean numbers of corpora lutea (CL) did not differ among the groups treated with 10, 20, 30 or 40 mg Folltropin or FSH-P, and the mean CL number was reduced (P<0.05) only in the 5 mg Folltropin group. Mean numbers of ova/embryos recovered, fertilized and transferable were greater (P<0.05) for the 10, 20 and 30 mg Folltropin groups than for the 5 mg group. The 40 mg Folltropin group and the FSH-P group were intermediate. The percentage of fertilized and transferable embryos did not differ over the dosages used in this experiment. In Experiment 2, mean numbers of CL were greater for the 9, 18 and 36 mg Folltropin groups than for the 4.5 mg group, with the 9 mg group being lower than the 36 mg group (P<0.05). The 18 mg group was intermediate and did not differ. Mean numbers of ova/embryos recovered and fertilized ova were greater for the 9, 18 and 36 mg groups (P<0.05) than for the 4.5 mg group. The percent of fertilized and mean number and percentage of transferable embryos did not differ among treatments. We conclude that Folltropin may be a satisfactory superovulatory replacement for FSH-P and that a dose of 18 to 20 mg Folltropin may be within the optimum superovulatory dosage range for beef heifers. Dosages of Folltropin of more than twice the optimum did not result in deterioration of ova/embryo quality.

Endocrine and superovulatory responses in heifers pretreated with FSH or bovine follicular fluid

This study examined the effects of altered serum FSH concentration on subsequent ovarian response to superovulation. Synchronized heifers were assigned randomly on Day 1 of the cycle (estrus = Day 0) to three pretreatment groups that consisted of 6-d of saline (7ml, s.c., b.i.d.; Group I), FSH-P (0.5 mg, i.m., b.i.d.; Group II) or charcoal-extracted bovine follicular fluid (BFF; 7 ml, s.c., b.i.d.; Group III) injections. Superovulation was initiated on Day 7 and consisted of FSH-P in decreasing dosages over 4 d (4,3,2,1 mg; i.m., b.i.d.), with cloprostenol (500 mug) on the morning of the third day. A second replicate with 14 heifers was conducted using the same protocol but twice the pretreatment dosage of FSH-P (1 mg) and BFF (14 ml). Endogenous plasma FSH decreased during BFF and FSH-P pretreatments compared to controls (P < 0.02). Endogenous FSH concentrations in both primed groups (II and III) were similar to control values (Group I) 12 h after the start of superovulation. Basal LH concentrations were not different between pretreatment groups. The interval from cloprostenol treatment to the preovulatory LH surge in Group III was 21.3 and 23.9 h longer (P < 0.0001) than it was in Groups I and II. The postovulation progesterone rise was delayed in Group III. The number of corpora lutea (CL) was lowest in the BFF-primed group (4.2 +/- 0.8) compared with the FSH-primed (7.4 +/- 1.3) and the control (12.0 +/- 1.8; P < 0.003) groups. In the FSH-primed group (0.68 +/- 0.06 cm(3)), CL volumes were larger than in the control group (0.45 +/- 0.03 cm(3)), whereas in the BFF-primed group (0.27 +/- 0.02 cm(3)) CL volumes were smaller compared with the control group (P < 0.0001). Mean FSH concentrations for 48 h preceding superovulation and the number of CL per cow were positively correlated (r = 0.55; P < 0.004; n = 26). We concluded that both FSH-P and BFF pretreatments decreased the superovulatory response of heifers to FSH-P. The mechanism for this would appear to be associated with reduced endogenous FSH prior to the start of superovulation.

Early postpartum reproductive profiles in Holstein cows with retained placenta and uterine discharges

Sixty Holstein cows were allocated to three groups. Twenty cows had retained placenta. The remaining cows were examined on d 14 postpartum and those with purulent discharges (n = 22) were assigned to one group and the remaining (n = 18) to a control group. Within each group, cows were given randomly either gonadotropin-releasing hormone (i.m., 200 micrograms) or saline on d 15 postpartum to evaluate the effect on changes in ovarian structures and plasma progesterone through 50 d postpartum and fertility. Corpora lutea were found in control cows by d 21, cows with uterine discharge by d 28, and cows with retained placenta by d 27. Maximum progesterone production during the first luteal phase was higher in control cows than in cows with purulent discharge or retained placenta (4.66 ng/ml compared with 3.23 and 3.34 ng/ml, respectively). Duration of the first corpus luteum was affected by clinical condition. Only 6.2% of cows with retained placenta had corpora lutea of normal duration (12 to 16 d), whereas 43.8 and 50.0% of cows with uterine discharge and control cows had normal postpartum luteal phases. Measures of fertility were not affected by gonadotropin-releasing hormone. Control cows had less days to conception (97) and fewer services per conception (1.6) than cows with retained placenta (134 and 2.5, respectively). Clinical group affected reproduction more than gonadotropin-releasing hormone did, possibly by altering ovarian function.

Association between energy balance and luteal function in lactating dairy cows

Our objective was to determine the relationship between energy balance and secretion of progesterone in lactating dairy cows. Eight primiparous and 24 multiparous lactating Holstein cows were studied from parturition to 100 d postpartum or conception. Cows calved normally and remained healthy throughout the study. All cows were fed ad libitum a total mixed diet formulated to satisfy requirements for maintenance and lactation. Intake of feed and production of milk per cow were measured twice daily. Body weight was determined weekly. Daily energy balance was determined by subtracting energy required for maintenance and lactation from intake of energy. Concentrations of progesterone were determined in milk sampled every 3rd d. For at least 4 successive d postpartum, 81% of cows were in negative energy balance. Variation in energy balance was explained largely by intake of energy. Duration of luteal phases was not associated with energy balance. Energy balance within 9 d postpartum was correlated positively with concentration of progesterone within second and third postpartum luteal phase. Postpartum interval to nadir and magnitude of nadir of energy balance interacted to reduce progesterone within second and third postpartum estrous cycles. Thus, in lactating cows, secretion of progesterone is reduced by spontaneous caloric deficit and is modulated by timing and magnitude of maximal caloric deficit. Spontaneous caloric deficit is a potential source of infertility in lactating dairy cows.

Effects of progesterone and weaning on LH and FSH responses to naloxone in postpartum beef cows

Two experiments were conducted to evaluate the effects of naloxone, an endogenous opioid receptor antagonist, on LH and FSH secretion in postpartum beef cows. In Experiment 1, 24 cows were divided into three equal groups. On day 15 postpartum, all cows were bled for 8 hr at 10 min intervals to evaluate LH secretory parameters. On day 18 postpartum, three treatments were administered: (a) saline at 0730 and 1130 hr; (b) 275 mg naloxone at 0730 and 1130 hr; (c) naloxone as in (b) above, plus this group was also treated with 50 mg progesterone (P4) twice daily from day 16 to day 19. In each treatment, jugular vein samples were collected at 10 min intervals from 0800 to 1600 hr. On day 19 the same treatments were administered at the same times, however, all cows were given 25 micrograms GnRH at 1200 hr to evaluate the LH secretory response. Naloxone increased mean LH concentration (P less than .05) and tended to increase pulse amplitude and frequency compared to controls. However, the most dramatic difference was due to P4 treatment which suppressed mean LH, pulse amplitude and frequency. Treatments had no effect on LH secretion in response to a 25 micrograms dose of GnRH. In Experiment 2, the effects of suckling on the naloxone response were examined in 16 postpartum cows. On day 21 postpartum, blood was collected at 10 min intervals for 8 hr and then calves were removed from half the cows. After 3 days of calf removal, all cows were sampled at 10 min intervals for 4 hr; then naloxone was injected after each 10 min sample at a dose rate of 200 mg/hr (33 mg per injection). Naloxone treatment and sampling continued for an additional 8 hr. Calf removal alone had very little effect on LH pulsatility. However, naloxone resulted in increased pulse frequency and mean LH compared to the control period. We conclude that LH release in the early postpartum cow is partially regulated by endogenous opioid peptides. We were unable to detect any effects on FSH secretion nor on pituitary sensitivity to exogenous GnRH.

Beta-carotene does not influence fertility in beef heifers

Eighty-four 18-month-old crossbred beef heifers, 3 to 4 months pregnant, were assigned by stratified randomization to either a high or low (control) beta-carotene (B-car) diet to determine the effect of long-term supplementation of B-car on reproductive performance. The heifers were followed through pregnancy, calving and subsequent breeding. The basal diet consisted of barley, canola meal and barley straw. Heifers supplemented by B-car received 625 mg B-car per day in the concentrate. Vitamin A and D complex injections were given monthly to all heifers. Heifers were bred by artificial insemination after Day 60 postpartum. Throughout the study heifers fed the B-car supplement had higher levels of B-car in plasma (> 300 ug/dl) (P < 0.01) than the heifers fed the control diet (< 50 ug/dl). Vitamin A status was satisfactory in all heifers throughout the study. Birth weight of calves, weight gain, and incidence of mortality were not influenced by B-car. For the control and B-car treatments, days postpartum to first normal luteal phase were 67.5 and 62.6 days; days postpartum to first detected estrus were 70.1 and 65.3, and services per conception were 1.24 and 1.29, respectively. Long-term supplementation of B-car increased prepartum plasma progesterone but had no effect on postpartum fertility.