Use of a gonadotropin-releasing hormone agonist or human chorionic gonadotropin for timed insemination in cattle

Three experiments were conducted to evaluate a synchronization protocol with AI at a predetermined time. In Exp. 1, 169 dairy heifers were assigned randomly to two groups: 1) timed AI (TAI), consisting of GnRH agonist injection (d 0, 1700), PGF2 alpha injection (d 7, 1700), GnRH agonist injection (d 8, 1700), and AI (d 9, 0800); and 2) AI at estrus (AIE), consisting of GnRH agonist injection (d 0, 1700), PGF2 alpha injection (d 7, 1700), and AI at detected estrus. Pregnancy rate was 25.8% for TAI (n = 89) compared with 48.7% for AIE (n = 80; P < .001). Experiment 2 was comparable to Exp. 1, but the second GnRH agonist injection in TAI was given 48 h after injection of PGF2 alpha. Heifers in TAI (n = 187) were inseminated at detected estrus if estrus occurred within 39 h after administration of PGF2 alpha (n = 47). Pregnancy rates were 45.5% for TAI and 48.0% for AIE (n = 177). Conception rate was reduced for TAI (45.5 [85/187] < 61.2% [85/139]; P < .005). In Exp. 3, the second injection of GnRH agonist, given at 48 h after injection of PGF2 alpha, was replaced with hCG (3,000 IU, i.m.). No differences in pregnancy rate were detected for TAI (52.9% [54/102]) vs AIE (56.1% [55/98]). Conception rate was reduced for TAI (52.9 [54/102] < 72.3% [55/76]; P < .005). Delaying the second GnRH agonist injection by 24 h improved pregnancy rate, but replacing the second injection of GnRH agonist with an injection of hCG did not prevent a reduction in conception rate.

Differential response of the luteal phase and fertility in cattle following ovulation of the first-wave follicle with human chorionic gonadotropin or an agonist of gonadotropin-releasing hormone

A series of experiments with Holstein heifers was conducted to develop the capability of inducing accessory corpus luteum (CL) with a GnRH agonist (Buserelin, 8 micrograms; GnRHa) or hCG (3,000 IU) to increase plasma progesterone concentrations (Exp. 1, 2, and 3) and to test whether induction of accessory CL with hCG will increase conception rates in heifers (Exp. 4) and lactating cows (Exp. 5). In Exp. 1, heifers were treated on d 5 after estrus with GnRHa (n = 8) or saline (n = 7); heifers in Exp. 2 received hCG (n = 5) or saline (n = 4) on d 5. Experiment 3 allowed a contemporary evaluation of heifers treated on d 5 with GnRHa (n = 6), hCG (n = 6), saline (n = 6), or GnRHa at d 5 and hCG at the time of the induced ovulation (n = 5). The GnRHa and hCG were equally effective in inducing an accessory CL (93% induction rate), but the subsequent increase in progesterone concentrations was greater in hCG-treated heifers. A greater half life of hCG may provide longer LH-like stimulation of the first-wave follicle and subsequent developing accessory CL or a greater luteotropic effect on the original CL. Induction of an accessory CL with hCG on d 5 or 6 after insemination did not increase pregnancy rates in fertile heifers (Exp. 4: hCG = 64.8% vs control = 62.9%; n = 243) or lactating dairy cows during summer heat stress (Exp. 5: hCG = 24.2% vs control = 23.5%; n = 201).

Effect of a gonadotropin-releasing hormone agonist on follicle recruitment and pregnancy rate in cattle

Two experiments were conducted to determine whether a GnRH agonist eliminated a potentially persistent first-wave dominant follicle (PDF) and recruited a new dominant follicle with improved fertility upon ovulation. In Exp. 1, five nonlactating Holstein cows were treated on d 7 (d 0 = estrus) with a norgestomet implant and PGF2 alpha (25 mg); a GnRH agonist was injected on d 9. On d 16, the norgestomet implant was removed and PGF2 alpha was injected. The corpus luteum (CL) regressed (5/5 cows), and plasma progesterone (P4) decreased (P < .01) from d 7 (P4 = 10.4 +/- .3) to 9 (P4 = 1.0 +/- .3 ng/mL). The GnRH agonist induced ovulation of the first-wave dominant follicle. New dominant follicles emerged by d 12 +/- 1. In all cows, removal of norgestomet implants and injection of PGF2 alpha on d 16 caused regression (P < .01) of the CL induced by the GnRH agonist. The GnRH agonist-recruited dominant follicles were highly estrogenic on d 17 (estradiol = 19.6 +/- .8 pg/mL) and ovulated on d 19.8 +/- .2 (5/5). In Exp. 2, 147 heifers at a synchronized estrus were assigned disproportionally but randomly to two treatments (GnRHa, n = 94; PDF, n = 53). On d 7, a used controlled internal drug releasing (CIDR-B) device was inserted into the vagina and PGF2 alpha was injected. On d 9, heifers in GnRHa were injected with GnRH agonist. The CIDR-B devices were removed and PGF2 alpha was injected into all heifers on d 16. Within 4 d after removal of CIDR-B devices, 96.8 and 94.3% of heifers in GnRHa and PDF were detected in estrus and inseminated. Pregnancy rates were GnRHa = 60.6% > PDF = 43.4% (P < .05). In summary, fertility after ovulation of a persistent first-wave dominant follicle is reduced, whereas induction of a new dominant follicle following injection of a GnRH agonist results in greater fertility.

Control and management of ovarian follicles in cattle to optimize fertility

Experiments were designed to elucidate the control of ovarian follicle turnover and the impact of follicular dynamics on the subsequent fertility of dairy cattle. An experimental model was established to examine the interrelationships of gene expression for steroid enzymes, the insulin-like growth factor system and inhibin production as associated with follicle selection, dominance and atresia. Follicular dynamics during the postpartum period and the oestrous cycle are shown to be altered markedly by the metabolic demands of lactation. The feeding of ruminally-inert fat stimulated follicular development and improved reproductive performance. The development of persistent follicles during oestrus synchronization causes a reduction in fertility that can be corrected by recruitment and selection of a new ovulatory follicle after the injection of a gonadotrophin-releasing hormone agonist. Present systems of oestrus synchronization need to consider both synchronization of follicular development and corpus luteal regression in order to optimize fertility. With current systems manipulating follicle development, the potential to implement a timed insemination programme to improve reproductive management exists. Ovulation of the first-wave dominant follicle with human chorionic gonadotrophin provides a means to markedly enhance concentrations of plasma progesterone in the luteal phase.

Characterization of the oviductal sperm reservoir in cattle

A reservoir for sperm has been found in the oviductal isthmus in several species. Sperm are apparently trapped in the reservoir by binding to the oviductal epithelium, although other factors may be involved. We hypothesized that binding sites for bovine sperm are limited to the isthmus and are regulated by the hormonal state of the cow. Ipsilateral oviducts were obtained from heifers that were preovulatory (in estrus), had ovulated recently (within 12 h), or were in diestrus (Day 10). The isthmic and the ampullar epithelium were milked out and incubated separately in serum-free (SFRE-199-2) medium, at 39 degrees C in 5% CO2. Frozen-thawed sperm from bulls were added to the epithelium and coincubated for 15 min. The number of spermatozoa that bound to explants was not affected by stage of cycle or by anatomic origin of the explants (p > 0.05). In an additional experiment, oviducts were infused with sperm in vivo and then prepared for scanning electron microscopy, which revealed that sperm were associated with ciliated epithelium in both the isthmus and ampulla. Thus, bovine sperm may form a reservoir in the isthmic end of the oviduct because it is the first oviductal region that they encounter.

Extension of corpus luteum lifespan and reduction of uterine secretion of prostaglandin F2 alpha of cows in response to recombinant interferon-tau

Two experiments tested the effect of recombinant ovine and bovine interferon-tau on corpus luteum lifespan, interestrous interval, and oxytocin-induced uterine secretion of prostaglandin F2 alpha. Cows received intrauterine injections of 100 micrograms of recombinant ovine interferon-tau plus 1.4 mg of BSA or of 1.5 mg of BSA alone in Experiment 1 and 200 micrograms of recombinant bovine interferon-tau plus 1.3 mg of BSA or 1.5 mg of BSA alone in Experiment 2. Twice daily injections (0700 and 1900 h) were split evenly between the uterine horns from d 14 to 24 of the experimental estrous cycle via an AI pipette in Experiment 1 and via intrauterine catheters in Experiment 2. On d 17, cows were injected with 100 IU of oxytocin, and plasma was collected for analysis of 13,14-dihydro-15-keto-prostaglandinF2 alpha. Recombinant ovine interferon-tau extended the lifespan of the corpus luteum (27.5 vs. 19.2 d) and interestrous interval (30.5 vs. 20.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandinF2 alpha, which peaked at 30 min for the BSA control group (210.8 pg/ml). Recombinant bovine interferon-tau also extended the lifespan of the corpus luteum (29.0 vs. 21.4 d) and interestrous interval (31.5 vs. 22.6 d) and abolished the oxytocin-induced increase in 13,14-dihydro-15-keto-prostaglandin F2 alpha, which peaked at 30 min for the BSA control group (205.6 pg/ml). In conclusion, recombinant ovine interferon-tau and recombinant bovine interferon-tau were effective antiluteolytic agents in cattle.

Effect of bovine interferon-tau on body temperature and plasma progesterone concentrations in cyclic dairy cows

We examined the effect of intramuscular injections of recombinant bovine interferon-tau on basal body temperature and plasma concentrations of progesterone in cows. Six mature, nonlactating Holstein cows were synchronized for estrus and assigned randomly to a replicated 3 x 3 Latin square design to receive 0, 1, or 5 mg of recombinant bovine interferon-tau intramuscularly on d 9, 12, or 15 of the estrous cycle. Rectal temperatures were measured, and blood was collected just prior to injection, at hourly intervals for 8 h, and at 10 and 12 h after injection. Treatment with 1 and 5 mg of recombinant bovine interferon-tau caused a rise in body temperature that peaked at 6 h (39.5 +/- .13 degrees C) and 4 h (40.3 +/- .13 degrees C), respectively. Analysis of homogeneity of regression for response curves indicated that 5 mg of recombinant bovine interferon-tau decreased plasma progesterone concentrations. This effect was not detected for the 1-mg dose of recombinant bovine interferon-tau. Intramuscular administration of 5 mg of recombinant bovine interferon-tau caused a hyperthermic response that was temporally associated with the decrease in plasma progesterone. Intramuscular administration of 1 mg of recombinant bovine interferon-tau caused a slight rise in temperature occurring 4 h later than that caused by 5 mg of recombinant bovine interferon-tau, and no decrease in plasma progesterone was detected. Recombinant bovine interferon-tau, administered at a 1-mg dose, warrants further study to determine whether it will alter survival rate of cattle embryos.

Protein intake and development of ovarian follicles and embryos of superovulated nonlactating dairy cows

Nonlactating Holstein cows (n = 12) were assigned randomly to one of two diets (approximately 30% concentrate) in a crossover design. Urea and soybean meal were used to increase CP content of diet from 12.3 to 27.4%. Mean concentrations of plasma urea were 9.8 and 21.3 mg/dl for respective diets. After 35 d on diets, cows were brought to a synchronized estrus (progestin implant plus PGF2 alpha injection). From d 10.5 to 14.5 following estrus, cows received i.m. injections of decreasing doses of FSH to initiate superovulation. On d 3 of FSH treatment, PGF2 alpha was injected with FSH. Cows were bred twice by AI when detected in estrus. Embryos were collected nonsurgically 6.5 d after breeding, and quality was assessed using visual, microscopic, and staining techniques. Development of follicles throughout this period was monitored using ultrasonography. Using ultrasonography, no differences were detected in the number or percentages of preovulatory, anovulatory, and ovulatory follicles induced during superovulation. Number of recovered embryos averaged eight per cow. Numbers and percentages of normal embryos, abnormal or retarded embryos, and unfertilized ova were similar between diets, as were the numbers and percentages of transferable and nontransferable embryos. Excess intake of CP failed to affect the growth or number of ovarian follicles and health and number of embryos of energy adequate, nonlactating dairy cows.

Stage-specific appearance of the mouse antigen TEC-3 in normal and nuclear transfer bovine embryos: re-expression after nuclear transfer

Bovine embryos, recovered from the uterus in vivo or derived from in vitro matured and in vitro fertilized oocytes, were investigated for the presence of the developmentally regulated mouse antigen TEC-3 by indirect immunofluorescence. During preimplantation embryo development TEC-3 is expressed on bovine morulae and blastocysts. It is absent from unfertilized and fertilized oocytes, and from all stages before the 32-cell stage. The finding that TEC-3 is not expressed before the onset of embryonic transcription, which occurs at the eight-cell stage in the bovine, but only when the embryonic genome is active, makes it a potential marker for studying nuclear reprogramming after nuclear transfer. Nuclear transfer embryos were made by electrical fusion of blastomeres from morulae derived in vivo with enucleated metaphase II oocytes. Indirect immunofluorescence with the TEC-03 antibody showed that the TEC-3 antigen, present on blastomeres of the morula stage embryo, disappeared after fusion and was expressed again when the nuclear transfer embryos developed to the morula and blastocyst stage. These data suggest that the bovine embryonic nucleus may be able to revert to the equivalent of an earlier developmental stage when transferred to ooplasm, and is then capable of following the normal developmental program.

Effects of calving-related disorders on prostaglandin, calcium, ovarian activity and uterine involution in postrartum dairy cows

Postpartum ovarian activity, uterine involution and plasma concentrations of calcium and 15-keto-13, 14 dihydro-prostaglandin F2alpha (PGFM) were assessed in dairy cows with retained fetal membranes (n=10) and milk fever (n=10) at parturition. In addition, calcium and PGFM were evaluated in dairy cows affected with uterine prolapse (n=10) and pyometra (n=14). Cows with retained fetal membrane averaged 24.2+/-3.7 d until their first postpartum ovulation, while controls averaged 29.0+/-3.7 d (P>0.10). In cows with retained fetal membranes, the difference in follicular activity between the contralateral and ipsilateral ovaries in relation to the previously gravid uterine horn was appreciably greater post partum when compared with that of the controls. Cows with milk fever had an average of 30.8+/-3.1 d until their first postpartum ovulation, while control cows had an average of 20.4+/-3.3 d (P<0.05). The mean diameter of the uterine horns in cows with milk fever was greater (P<0.05) compared with that of the controls between Days 15-32 post partum. Concentrations of plasma calcium were lower in cows with retained fetal membranes within 24 h after parturition and during the first week post partum than in the controls (6.27+/-0.18 vs 7.40+/-0.18 mg/100ml, P<0.05). Concentration of calcium was lower (P<0.05) in cows with milk fever on Day 1 prior to treatment (4.68+/-0.40 < 5.8+/-0.45 mg/100ml) than in control cows; however, the calcium (Ca) level was not different during the subsequent 7 d post partum after treatment. Cows with uterine prolapse had lower concentrations of Ca during the first 7 d post partum than the controls (6.10+/-0.15 vs 7.33+/-0.12mg/100ml; P<0.01). Cows with pyometra had higher (P<0.05) concentrations of plasma PGFM than the controls (208.+/-13.2 > 138.1+/-15.2).

Developmental changes in embryonic resistance to adverse effects of maternal heat stress in cows

The objective of this study was to determine whether bovine embryos become more resistant to deleterious effects of maternal heat stress as early embryonic development progresses. Superovulated, lactating Holstein cows were bred by AI and assigned to be heat stressed on d 1, 3, 5, or 7 of pregnancy (d 0 = day of estrus) or not heat stressed (control). Embryos were retrieved from the uterus on d 8 and evaluated for viability and stage of development. Compared with embryos of control cows, embryos of cows receiving heat stress on d 1 had decreased viability and development. Maternal heat stress on other days had no detrimental effect on embryonic viability or stage of development. Bovine embryos become more resistant to adverse effects of maternal heat stress as pregnancy progresses; substantial resistance develops by d 3. This information may be useful in design of environmental modification systems that provide cooling at critical periods of gestation to enhance pregnancy rates during summer in hot climates.

Effects of induction of low plasma progesterone concentrations with a progesterone-releasing intravaginal device on follicular turnover and fertility in cattle

The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF2 alpha (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (approximately 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF2 alpha injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 +/- 1.6 mm, 20 +/- 1.3 mm and 10 +/- 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5-9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of environmental heat stress on follicular development and steroidogenesis in lactating Holstein cows

Lactating Holstein cows were utilized over two replicate periods (July and September, 1990) to examine the effect of summer heat stress on follicular growth and steroidogenesis. On day of synchronized ovulations, cows were assigned to shade (n=11) or no shade (n=12) management systems. Follicular development was monitored daily by ultrasonography until ovariectomy on Day 8 post estrus. At time of ovariectomy, dominant and second largest follicles were dissected from the ovary. Aromatase activity and steroid concentrations in dominant and subordinate follicles were measured. Acute heat stress had no effects on patterns of growth of first wave dominant and subordinate follicles between Days 1 and 7 of the cycle. Compared with shaded cows, the heat stressed cows did not have suppression of medium size (6 to 9 mm) follicles between Days 5 and 7. A treatment x follicle interaction was detected (P<0.01) for follicular diameter and fluid volume at Day 8. Dominant follicles in shade were bigger (16.4>14.5 mm) and contained more fluid (1.9>1.1 ml) than dominant follicles in no shade. Conversely, subordinate follicles in no shade were bigger (10.1>7.9 mm) and contained more fluid (0.4>0.2 ml) than subordinate follicles in shade. Concentrations of estradiol in plasma and follicular fluid were higher (P<0.01) in July than in September. Heat stress appears to alter the efficiency of follicular selection and dominance, and to have adverse effects on the quality of ovarian follicles.

Endocrine and ovarian responses associated with the first-wave dominant follicle in cattle

To examine endocrine and biochemical differences between dominant and subordinate follicles and how the dominant follicle affects the hypothalamic-pituitary-ovarian axis in Holstein cows, the ovary bearing the dominant follicle was unilaterally removed on Day 5 (n = 8), 8 (n = 8), or 12 (n = 8) of synchronized estrous cycles. Follicular development was followed daily by ultrasonography from the day of detected estrus (Day 0) until 5 days after ovariectomy. Aromatase activity and steroid concentrations in first-wave dominant and subordinate follicles were measured. Intact dominant and subordinate follicles were cultured in 4 ml Minimum Essential Medium supplemented with 100 microCi 3H-leucine to evaluate de novo protein synthesis. Five days after unilateral ovariectomy, cows were resynchronized and the experiment was repeated. Follicular growth was characterized by the development of single large dominant follicles, which was associated with suppression of other follicles. Concentrations of estradiol-17 beta (E2) in follicular fluid and aromatase activity of follicular walls were higher in dominant follicles (438.9 +/- 45.5 ng/ml; 875.4 +/- 68.2 pg E2/follicle) compared to subordinate follicles (40.6 +/- 69.4 ng/ml; 99.4 +/- 104.2 pg E2/follicle). Aromatase activity in first-wave dominant follicles was higher at Days 5 (1147.1 +/- 118.1 pg E2/follicle) and 8 (1028.2 +/- 118.1 pg E2/follicle) compared to Day 12 (450.7 +/- 118.1 pg E2/follicle). Concentrations of E2 and androstenedione in first-wave dominant follicles were higher at Day 5 (983.2 +/- 78.2 and 89.5 +/- 15.7 ng/ml) compared to Days 8 (225.1 +/- 78.6 and 5.9 +/- 14.8 ng/ml) and 12 (108.5 +/- 78.6 and 13.0 +/- 14.8 ng/ml). Concentrations of progesterone in subordinate follicles increased linearly between Days 5 and 12 of the estrous cycle. Plasma concentrations of FSH increased from 17.9 +/- 1.4 to 32.5 +/- 1.4 ng/ml between 0 and 32 h following unilateral removal of the ovary with the first-wave dominant follicle. Increases in plasma FSH were associated with increased numbers of class 1 (3-4 mm) follicles in cows that were ovariectomized at Day 5 or 8 of the cycle. Unilateral ovariectomy had no effects on plasma concentrations of LH when a CL was present on the remaining ovary. First-wave dominant follicles incorporated more 3H-leucine into macromolecules and secreted high (90,000-120,000) and low (20,000-23,000) molecular weight proteins that were not as evident for subordinate follicles at Days 8 and 12.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of bovine interferon-alpha I1 on pregnancy rate in heifers

Bovine interferon-alpha I1 (bIFN-alpha) may be useful for enhancing fertility in sheep and cattle because it has extensive sequence homology with ovine and bovine trophoblast protein-1 and, like those proteins, extends corpus luteum lifespan. To test the effectiveness of bIFN-alpha to enhance fertility, several experiments were performed in which inseminated heifers were given i.m. injections of bIFN-alpha approximately at the time of embryo-mediated signals that result in maintenance of the corpus luteum. In Exp. 1, heifers given 20 mg of bIFN-alpha daily from d 14 to 17 tended (P less than .07) to have lower pregnancy rates at d 110 to 112 of gestation (36/75; 48% vs 43/72; 60%). Similar results were obtained in Exp. 2 when heifers received a single injection of 40 mg of bIFN-alpha or placebo at d 13 after estrus; pregnancy rates at d 42 were 39/104 (38%) for bIFN-alpha and 47/98 (48%) for placebo. In Exp. 3, heifers were given gradually increasing doses of bIFN-alpha or placebo from d 11 to 19, because such a regimen had been shown to reduce the number of heifers experiencing hyperthermia after bIFN-alpha injection. Pregnancy rates were 42/95 (44%) for bIFN-alpha and 62/111 (56%) for placebo. Across all three experiments, pregnancy rates were lower (P less than .01) for heifers treated with bIFN-alpha (117/274; 43%) than for heifers treated with placebo (152/281; 54%). In conclusion, these results demonstrate that, under the administration systems used, bIFN-alpha does not increase pregnancy rate, but rather tends to reduce it.

Thermoprotection of preimplantation bovine embryos from heat shock by glutathione and taurine

To determine if deleterious effects of heat shock on embryos could be reduced in vitro by glutathione or taurine, morulae from superovulated cows were placed in modified Hams-F10 medium supplemented with 50 nM glutathione (GSH), 50 mM taurine or neither. Morulae were incubated for 2 hours at 38.5 degrees C, then at 42.0 degrees C (heat shock) or 38.5 degrees C for 2 hours and followed by incubation at 38.5 degrees C for 20 hours. Neither GSH nor taurine enhanced viability or blastocyst development at 38.5 degrees C. At 42.0 degrees C, however, GSH and taurine increased (P less than 0.02) viability (73%, 41% and 26% live for GSH, taurine and control); GSH increased (P less than 0.05) blastocyst development (55% for GSH vs. 30% for control). In conclusion, partial thermoprotection of bovine embryos from heat shock can be achieved in vitro by administration of GSH. Taurine is only slightly effective.

Ovariectomy by colpotomy in cows

For the purpose of collecting active ovarian structures for cell culture, unilateral ovariectomy (n = 34 ovaries) was performed per vagina on 17 dairy cows having normal estrous cycles, bilateral ovariectomy was performed on 9 (n = 18 ovaries) dairy cows, and corpora lutea (n = 13) were removed from 11 beef cows having normal estrous cycles. None of the cows was clinically ill after the operation. Nine of 37 cows developed adhesions of both uterine horns and the body of the uterus. Three instruments were used to perform colpotomy. The described surgical technique for removal of the ovaries or corpora lutea is practical and inexpensive, and has low morbidity associated with it.

Effects of postinsemination progesterone supplementation on fertility and subsequent estrous responses of dairy heifers

The objective of Experiment I, replicated twice, was to evaluate whether fertility of estrus-synchronized dairy heifers could be improved by postinsemination progesterone supplementation. Estrous cycles were synchronized using two injections of prostaglandin (PG) F(2alpha) adiministered 11 days apart. Heifers displaying estrus were inseminated and assigned to control (n = 155) and treated (n = 159) groups. Treatment consisted of intravaginal insertion of controlled internal drug release (CIDR) devices for Days 7 to 13 (Day 0 = day of estrus). The conception rate for CIDR-treated heifers (57.9%) did not differ significantly from that of the controls (53.6%). The return-to-estrus rate and pattern of return estruses were not affected by treatment, but indicated that early embryonic mortality may have occurred in some of the heifers diagnosed nonpregnant. The objective of Experiment II was to evaluate if used CIDR devices were effective in resynchronizing returns to estrus in previously synchronized inseminated but nonpregnant and noninseminated heifers. Estrous cycles of dairy heifers of breeding age were synchronized with PGF(2alpha). Heifers displaying estrus were assigned to be inseminated (n = 117) or not inseminated (n = 35). All heifers were treated with 9-day used CIDR devices for Days 17 to 22 after synchronized estrus in order to resynchronize returns to estrus. Of the inseminated but nonpregnant heifers (n = 41), 78.1% were detected in estrus after CIDR removal (versus 94.3% of noninseminated heifers [n = 35]; P < 0.05) and 61.0% of the estruses occurred within 4 days of CIDR removal (versus 91.4% of noninseminated; P < 0.05). Estruses of synchronized inseminated nonpregnant heifers occurred over a longer period compared with those of noninseminated heifers (P < 0.025). The results indicate that response to the resynchronization protocol was altered by the outcome (early embryo death or failed fertilization) of the previous unsuccessful insemination, and support the hypothesis that delayed returns to estrus can be attributable to a pregnancy which was initiated but failed to establish itself. Such factors should be considered when evaluating responses of cattle to treatments designed to enhance fertility.

Stimulation of proliferation of bovine placental cells by products of activated mononuclear leukocytes

Culture medium conditioned with concanavalin A-stimulated mononuclear leukocytes was tested for its ability to stimulate in vitro proliferation of bovine placental cells. The crude preparation of cytokines caused a dose-dependent increase in [3H]thymidine uptake into cells obtained by trypsinization of fresh bovine placentae and placental cell lines established from cellular outgrowths of long-term bovine placental cultures, but had no effect on growth of 3T3 fibroblasts. Growth of trypsinized placental cells was not enhanced by culture in the presence of interleukin-2, interferon-beta 2, interferon-gamma, or tumor necrosis factor-alpha. These results corroborate those of murine studies, suggesting a growth-promoting role for cytokines released into the maternal-fetal interface.

Follicular dynamics and superovulatory response in Holstein cows treated with FSH-P in different endocrine states

The effect of follicular and/or endocrine environments on superovulatory response was tested. Eighteen nonlactating Holstein cows were superovulated with 32 mg FSH-P given in decreasing doses at 12-h intervals plus two injections of prostaglandin F2-alpha (25 mg each) on the third day of treatment. Cows were assigned randomly to treatments: T1, superovulatory treatment initiated on estrous cycle Day 10.5; T2, CIDR (intravaginal device containing 1.9 g of progesterone) inserted from Days 3 to 9 and superovulation initiated on Day 6.5; T3, identical to T2 but Buserelin (GnRH agonist) was injected (8 microg, i.m.) on Day 3 at the time of CIDR insertion. Embryos were recovered on Day 7 after the superovulatory estrus. Cows were examined daily by ultrasonography and blood was collected for progesterone and estradiol determinations. Mean diameter of the dominant follicle (frequency of first-wave dominant follicle) at the beginning of FSH injections was 13.7 mm (4/6), 11.2 mm (6/6) and 8.7 mm (6/6) (P<0.01) for T1, T2 and T3, respectively. Following initiation of superovulation, follicles moved into larger follicle classes (Class I, <3 mm; Class II, 3 to 4 mm; Class III, 5 to 9 mm; Class IV >9 mm) earliest in T1 (P<0.01). Cumulative follicular diameter and plasma concentrations of estradiol at Day 4 of superovulation were higher (P<0.01) in T1 (200 mm, 82 pg/ml) compared with T2 (123 mm, 24 pg/ml) and T3 (130 mm, 18 pg/ml). Proportion of cows in estrus prior to 12 h vs 12 to 24 h differed (P<0.05) between groups (T1: 5 vs 1; T2: 2 vs 4; T3: 1 vs 5). Mean number of follicles on the last day of superovulation treatment, number of CL and number of embryos plus unfertilized ova recovered were 17.5, 12.2 and 13.3; 13.8, 10 and 8.2 (P<0.1) and 8.7, 4.5 and 2.3 (P<0.05) for T1, T2 and T3, respectively. The developmental stage of the dominant follicle was associated with not only the number of ovulations, but also the size and periestrous concentrations of plasma estradiol associated with the recruited follicles.