F. Moreira

Effects of hormonal treatments on reproductive performance and embryo production

Developments in the use of drugs to improve reproduction and embryo production have focused on estrus and ovulation synchronization protocols and embryonic survival. Protocols for synchronization of ovulation eliminate the need for detection of estrus and allow timed insemination of all cows enrolled. Various estrogenic, progestational, GnRH and PGF2 alpha-like drugs are used to synchronize follicle development, CL regression and induction of ovulation. Strategies are discussed to optimize such programs to maximize herd pregnancy rates. Use of bovine Somatotrophin (bST) in combination with the Ovsynch protocol resulted in increased pregnancy rates, indicating possible effects on oocyte and embryonic development. Treatment of embryo donor cows with bST reduced the proportion of unfertilized oocytes and increased the number of transferable embryos. Furthermore, bST increased pregnancy rate when given to the recipient. Sub-luteal plasma progesterone concentrations after insemination have been associated with lower pregnancy rates. Injection of hCG on day 5 post-insemination resulted in induction of an accessory CL, increased plasma progesterone concentrations and increased conception rates. Strategies involving the use of sustained GnRH agonists to enhance CL development and alter follicular development are considered for future programs to enhance pregnancy rates.

Effects of growth hormone and insulin-like growth factor-I on development of in vitro derived bovine embryos

The objectives of this study were to determine whether the addition of growth hormone (GH) to maturation medium and GH or insulin-like growth factor-I (IGF-I) to culture medium affects development of cultured bovine embryos. We matured groups of 10 cumulus-oocyte complexes (COCs) in serum-free TCM-199 medium containing FSH and estradiol with or without 100 ng/ml GH. After fertilization, we transferred groups of 10 putative zygotes to 25 microl drops of a modified KSOM medium containing the following treatments: non-specific IgG (a control antibody, 10 microg/ml); GH (100 ng/ml) + IgG (10 microg/ml, GH/IgG); IGF-I (100 ng/ml) + IgG (10 microg/ml, IGF/IgG); antibody to IGF-I (10 microg/ml, anti-IGF); GH (100 ng/ml) + anti-IGF (10 microg/ml GH/anti-IGF); IGF-I (100 ng/ml) + anti-IGF (10 microg/ml, IGF/anti-IGF); no further additions (control). We repeated the experiment six times. Adding GH to the maturation medium increased cleavage rates at Day 3 compared to control (87.3 +/- 1.2% > 83.9 +/- 1.2%; P < 0.05) but had no effects on blastocyst development at Day 8. At Day 8, blastocyst development was greater (P < 0.01) for GH/IgG (24.8 +/- 2.5%) and IGF/IgG (33.7 +/- 2.5%) than for IgG (16.1 +/- 2.1%) and greater for IGF/IgG than for GH/IgG (P < 0.02). Blastocyst development at Day 8 did not differ between anti-IGF (20.4 +/- 1.8%) and GH/anti-IGF (24.1 +/- 1.9%) or IGF/anti-IGF (17.7 +/- 1.9%), but it was greater for GH/anti-IGF than for IGF/anti-IGF (P < 0.05). The Day 8 blastocysts of GH/IgG and IGF-I/IgG groups had a higher (P < 0.01) number of cells than the IgG group. The addition of anti-IGF-I eliminated the effects of IGF-I on cell number but did not alter GH effects. In conclusion, both GH and IGF-I stimulate embryonic development in cattle and GH effects may likely involve IGF-I-independent mechanisms.

Effect of body condition on reproductive efficiency of lactattng dairy cows receiving a timed insemination

Body condition may influence pregnancy rates to a timed insemination (Ovsynch/TAI) protocol and affect the economical performance of dairy farms. The objectives were to compare pregnancy rates using the Ovsynch/TAI protocol for the first service of lactating dairy cows with body condition scores < 2.5 (scale: 1 to 5, low BCS group) versus > or = 2.5 (control group) and to estimate the economic impact of the effect of body condition on reproductive performance. At 63 +/- 3 d post partum, cows were assigned to 2 experimental groups (low BCS = 81; control = 126), and were treated with GnRH at d 0 and with PGF2alpha 7 d later. At 48 h after PGF2alpha, cows received an injection of GnRH and were inseminated 16 h later. Pregnancy rates to the Ovsynch/TAI protocol were lower for the low BCS group than for the control group at 27 d (18.1 +/- 6.1% < 33.8 +/- 4.5%; P<0.02) and at 45 d (11.1 +/- 5.4% < 25.6 +/- 4.1%; P<0.02) after insemination. Economic analysis indicated that reducing the percentage of the herd in low body condition increases net revenues per cow per year. Body condition influenced pregnancy rates to the Ovsynch/TAI protocol.

Evaluation of timed insemination during summer heat stress in lactating dairy cattle

We wished to compare the effect of summer heat stress on pregnancy rate in cows that were inseminated at a set interval associated with a synchronized ovulation vs those inseminated upon routine estrus detection. The study was carried out on a commercial dairy farm in Florida from May to September 1995. Lactating dairy cows were given PGF2 alpha (25 mg i.m.) at 30 + 3 d postpartum and randomly assigned to be inseminated at a set time (Timed group) or when estrus was detected (Control group). Cows in the Timed group were synchronized by sequential administration of Buserelin (8 micrograms i.m.) on Day 0 at 1600 h, PGF2 alpha (25 mg i.m.) on Day 7 at 1600 h and Buserelin (8 micrograms i.m.) on Day 9 at 1600 h. They were inseminated on Day 10 between 0800 and 0900 h (Day 9 + 16 h). Cows in the Control group were given PGF2 alpha at 57 + 3 d postpartum and inseminated when detected in estrus. Estrus detection or insemination rate for control insemination cows was 18.1 +/- 2.5% versus 100% for time inseminated cows (P < 0.01). Mean interval from PGF2 alpha to insemination was shorter for time inseminated cows (3 +/- 2.1 d < 35.5 +/- 1.9 d; P < 0.01). Pregnancy rate was greater for time inseminated cows (13.9 +/- 2.6 > 4.8 +/- 2.5%; P < 0.01) as was overall pregnancy rate by 120 d postpartum (27.0 +/- 3.6 > 16.5 +/- 3.5%; P < 0.05). Number of days open for cows conceiving by 120 d postpartum was less for time inseminated cows (77.6 +/- 3.8 < 90.0 +/- 4.2 d; P < 0.05), as was interval to first service (58.7 +/- 2.1 < 91.0 +/- 1.9 d; P < 0.01). Services per conception were greater for time inseminated cows (1.63 +/- 0.10 > 1.27 +/- 0.11; P < 0.05). The timed insemination program did improve group reproductive performance. However, the timed insemination program will not protect the embryo from temperature-induced embryonic mortality, but management limitations induced by heat stress on estrus detection are eliminated. An economical evaluation of the timed insemination program indicates an increase in net revenue per cow with implementation of timed insemination for first service during the summer months.

Bovine somatotropin increases embryonic development in superovulated cows and improves post-transfer pregnancy rates when given to lactating recipient cows.

Previous studies indicated that the use of bovine somatotropin (bST) in concurrence with a timed artificial insemination (TAI) protocol increased pregnancy rates. However, the mechanisms for such a bST effect on fertility were not clear. Objectives of this study were to determine the effects of bST on fertilization and early embryonic development after cows received a superovulation treatment, test whether embryos recovered from bST-treated cows were more likely to survive after transfer to recipients, and evaluate whether treatment of recipient cows with bST affects pregnancy rates. Lactating (n = 8) and nonlactating (n = 4) Holstein donor cows were superovulated, inseminated at detected estrus and assigned to a nontreated control group or to a treatment group receiving a single injection of bST (500 mg, sc) at insemination. Embryos were nonsurgically flushed 7 days after AI and frozen in ethylene glycol for direct transfer. Embryos derived from bST-treated (bST-embryos) or control (control-embryos) donors were transferred to lactating Holstein recipient cows that received either bST treatment 1 day after estrus (500 mg, sc; bST-recipients) or were untreated controls (control-recipients). Thus, there were four treatment groups: control-embryos/control-recipients (n = 43), bST-embryos/control-recipients (n = 41), control-embryos/bST-recipients (n = 37), and bST-embryos/bST-recipients (n = 60). Pregnancy was determined by palpation per rectum 33-43 days after embryo transfer. Unfertilized ova per flush was less for bST than for control (1.0 +/- 0.9 < 3.7 +/- 0.9; P < 0.04). Percentage of transferable embryos was greater for bST than for control (77.2% > 56.4%; P < 0.01). Number of blastocysts per flush was greater for bST than for control (2.4 +/- 0.7 > 0.4 +/- 0.7; P < 0.04). Pregnancy rates following embryo transfer were 25.6% for control-recipient/control-embryo, 43.2% for bST-recipient/control-embryo, 56.1% for control-recipient/bST-embryo, and 43.3% for bST-recipient/bST-embryo. Transfer of bST-embryos increased pregnancy rates compared with transfer of control-embryos (P < 0.04). An interaction between embryo and recipient treatments (P < 0.05) indicated that treatment of recipient cows with bST increased pregnancy rates as compared to control-recipients that received a control-embryo. However, there was no additive effect when bST-recipients received a bST-embryo. Administration of bST at AI decreased the number of unfertilized ova, increased the percentage of transferable embryos, and stimulated embryonic development to the blastocyst stage. Moreover, bST affected both early embryonic development and recipient components to increase pregnancy rates following embryo transfer.

Strategies to optimize reproductive efficiency by regulation of ovarian function.

Pregnancy rate to the Ovsynch protocol can be improved if cows are presynchronized (i.e., two PGF(2alpha) injections given 14 days apart and the second injection of PGF(2alpha) given 12 days prior to the first GnRH of the Ovsynch program) so that a greater proportion of cows during the Ovsynch protocol ovulate to the first GnRH injection and have a CL at PGF(2alpha) injection. Pregnancy rates were normal in anestrous cows (39.6%) if they ovulated to both injections of GnRH. Estradiol cypionate (ECP) can be used to replace GnRH to induce ovulation as a modification of the Presync-Ovsynch program (i.e., Presync-Heatsynch). Pregnancy rates after TI were 37.1+/-5.8% for Presync-Ovsynch compared to 35.1+5.0% for Presync-Heatsynch. Use of ECP to induce ovulation was an alternative to GnRH in which greater uterine tone, ease of insemination and occurrence of estrus, improved acceptance by inseminators. A GnRH agonist (Deslorelin; 750 microg) implant inserted at 48 h after injection of PGF(2alpha), as a component of the Ovsynch protocol, induced ovulation, development of a normal CL and delayed follicular growth until 24 d after implant insertion. Utilization of Deslorelin implants (450 microg and 750 microg) to induce ovulation compared to GnRH (100 microg) within the Ovsynch protocol resulted in 27 d pregnancy rates (GnRH 100 microg, 39%; Deslorelin implants 450 microg, 40% and 750 microg, 27.5%) with 12.7%, 5.0% and 9.5% embryonic losses by 41 d of pregnancy, respectively. Induction of an accessory CL with injection of hCG on day 5 after insemination improved conception rates by 7.1%. Bovine somatotrophin injected at first insemination following a Presync-Ovsynch program in cycling-lactating dairy cows increased 74 days pregnancy rates (57.1%>42.6%).

Influence of Deslorelin (GnRH-agonist) implant on plasma progesterone, first wave dominant follicle and pregnancy in dairy cattle

The objectives of this study were to investigate the effect of a synthetic GnRH-agonist (Deslorelin) implant on CL function and follicle dynamics when administered 48 h after PGF2 alpha, in a timed-insemination protocol, and to determine if the incorporation of a Deslorelin implant into a timed-insemination protocol to synchronize ovulation would be beneficial to the establishment of pregnancy. In Experiment 1, 15 non lactating cyclic Holstein cows received Buserelin (8 micrograms, i.m.) on Day-9, Lutalyse (25 mg, i.m.) on Day-2, and then on Day 0 received either a Deslorelin implant (700 micrograms, s.c.; n = 5), Buserelin (8 micrograms, i.m.; n = 5), or no treatment (control; n = 5). Blood samples were collected on Days-9, -2, 0 and thereafter daily until the next ovulation. Ovaries were scanned by ultrasound on Days-9, -2, 0, 1 (day of ovulation) and 3 times a week thereafter until a subsequent ovulation. From Days 0 to 15, the rate of increase of plasma progesterone (P4) was greater (P < 0.01) for Deslorelin than for control and Buserelin. Establishment of the first-wave dominant follicle (FWDF) as a Class 3 (> 9 mm) follicle was delayed (P < 0.01) with Deslorelin (14.2 +/- 1.3 d) compared with the control (4.6 +/- 1.3 d) and Buserelin (5.0 +/- 1.5 d) treatments. The FWDF resumed growth after Day 13 in all 5 Deslorelin-treated cows, and 2 cows ovulated spontaneously. In 1 Deslorelin-treated cow, the FWDF regressed, and a second-wave dominant follicle ovulated, while 2 other Deslorelin cows failed to ovulate until after Day 36. The cumulative numbers of Class 2 and 3 follicles was lowest in the Deslorelin group (P < 0.01), while the cumulative number of Class 1 follicles was highest (Deslorelin > Buserelin > Control; P < 0.01). The number of days to CL-regression and days to subsequent estrus did not differ (P > 0.05) among treatments. In Experiment II, 16 lactating potentially subfertile (body condition score 2.25) cows received Cystorelin (100 micrograms, i.m.; Day-9), Lutalyse (25 mg, i.m.; Day-2), and either a Cystorelin injection (100 micrograms, i.m.; n = 8) or Deslorelin implant (700 micrograms, s.c.; n = 8) on Day 0 and inseminated 16 h later. Deslorelin-treated cows had a higher plasma P4 concentration between Days 0 and 16 (P < 0.05) than the 2 other groups, and 5 of the 8 cows in this group were pregnant (Day 45, palpation) compared with 1 of 8 cows in the Cystorelin group (P < 0.05). Incorporation of a Deslorelin implant into a timed-insemination protocol enhanced the pregnancy rate in cows of poor body condition. The results support the hypothesis that enhanced CL function and delayed establishment of the first-wave dominant follicle may enhance embryo survival.

Use of medroxyprogesterone acetate (MAP) in lactating Holstein cows within an Ovsynch protocol: follicular growth and hormonal patterns

To evaluate the effects of incorporating medroxyprogesterone acetate (MAP) in an Ovsynch protocol, cyclic lactating dairy cows were assigned randomly to two groups (control and MAP, n=8 each). Ovsynch treatment (Day 0: GnRH, Day 7: PG, Day 9: GnRH) was initiated at random stages of the estrous cycle (control) and an intravaginal polyurethane sponge impregnated with 300mg of MAP was inserted intravaginally in the MAP group at Day 0 and removed at Day 7 of the Ovsynch protocol (MAP treatment). Ovaries were scanned daily from Day 0 until the second GnRH treatment on Day 9 and from then every 6h for 36 h. Milk samples were collected three times weekly starting 17 days before the initiation of treatment to determine the stage of the cycle at the beginning of the Ovsynch protocol. Blood samples were collected to monitor estradiol (E2), progesterone (P4), LH, and 15-ketodihydro-PGF(2alpha) (PGFM) by RIA. Response to the first GnRH treatment varied with the stage of the cycle at the time of initiation of treatment, as cows in metestrous and late diestrous did not ovulate. In cows ovulating, growth rate of the new follicle was not affected by the addition of MAP. No treatment differences were found in E2 concentrations which reached a maximum at Day 9, consistent with the maximum follicular size. At Day 7, cows with luteal concentrations of P4 had increased concentrations of PGFM, but cows with basal P4 did not show an active release of prostaglandins. There were no treatment differences in the ovulatory response to the second GnRH-induced ovulation, with 11 of the 16 cows ovulating between 16 and 32 h. The addition of MAP to the Ovsynch protocol could not mimic the normal high progesterone levels needed to prevent premature ovulations in those cows with premature CL regression.