The effect of treatment with bovine somatotropin (BST) on the superovulatory response of cattle

Embryo transfer in Bos indicus cattle

In the present short review superovulation treatments commonly used for Bos taurus and/or Bos indicus will be addressed with emphasis in recent superstimulation protocols associated with pharmacological manipulation of the follicular dynamics to improve donor management and potentially embryo yield. Results obtained after superovulation treatments in which the time of LH surge is selectively delayed as an attempt to improve embryo yield are presented and discussed.

Effects of growth hormone on female reproductive organs

During the last decade many experiments have been performed to study the effects of growth hormone (GH, somatotropin) on reproductive functions. Most of the studies found only slight or no effects of GH treatment, both on the oestrous cycle and on gonadotropin, progesterone. or oestrogen serum levels. In GH-treated animals, elevated levels of insulin-like growth factor I and GH in the serum could be correlated with an increased number of small (< 5 mm in diameter) ovarian follicles, possibly as a consequence of a reduction of apoptosis and follicular atresia. There is still controversy over the effects of GH on in vivo and in vitro embryo production and on the gestation period. Recent studies produced some evidence that GH-receptor is expressed in ovarian tissue, implying a direct role for GH in the ovary.

Effect of long-term treatment with recombinant bovine somatotropin and estradiol on hormone concentrations and ovulatory response of superovulated cattle

The objective was to assess effects of long-term treatment with recombinant bovine somatotropin (bST) and estradiol-17beta (E2) on the number of follicles that ovulated in response to FSH. Non-lactating Holstein and Jersey cows (Trial 1, n=27) and Angus cows and heifers (Trial 2, n=35) received two ear implants of E2 and biweekly injections of bST in a 2 x 2 arrangement of treatments. Estradiol implants were removed 74.6 +/- 1.1 d after insertion and 18.1 +/- 0.9 d after the last biweekly injection of bST. Cows were stimulated with FSH-P beginning 2 d after removal of E2 implants, and PGF2alpha (PGF) was given on the third day of FSH treatment. Ovaries were collected to determine the number of CL at 1 to 2 wk after treatment with PGF. In Trial 2 only, cattle were inseminated at estrus and embryos were collected 6 to 8 d later. Implants of E2 increased (P < 0.01) serum E2 8-fold initially and E2 was still elevated 5-fold at removal of implants. Injections of bST increased (P < 0.01) serum growth hormone (GH) 15-fold and insulin-like growth factor-I (IGF-I) 3-fold. In Trial 1, number of CL was increased by the combination of bST+E2 (P < 0.01). In Trial 2, E2 increased the number of CL (P < 0.05), and bST increased the number of total ova and transferable embryos (P < 0.01). We conclude that long-term treatment with bST and E2 may interact to enhance follicular development and ovulatory response to FSH.

Messenger RNA expression and protein localization of growth hormone in bovine ovarian tissue and in cumulus oocyte complexes (COCs) during in vitro maturation

The aim of this study was to investigate whether bovine cumulus oocyte complexes (COCs) obtained from 2 to 8 mm follicles synthesize growth hormone (GH) during in vitro maturation. In addition the expression of growth hormone releasing hormone receptor (GHRH-r) in the COCs before and after in vitro maturation was investigated. Therefore, COCs obtained from small and medium sized follicles were cultured in M199 supplemented with 10% FCS and gonadotropins for 24 hr. At 0, 6, 12, and 24 hr after the onset of culture, COCs were removed and were prepared for immunohistochemical staining to detect the presence of GH. In addition, sections of ovary were stained to study the differential localization of GH in the ovary. At 0 and 24 hr COCs were removed and together with samples from granulosa cells and theca cells were prepared for reverse transcriptase polymerase chain reaction (RT-PCR) to assess the expression of mRNA of GH and GHRH-r. Within COCs, cumulus cells and oocytes showed GH immunoreactivity, while expression of GH mRNA was only found in the oocyte. At the onset of culture, oocytes and cumulus cells in the majority of COCs generally showed moderate and strong staining intensity for GH, respectively. While GH staining in the cumulus cells did hardly change during 24 hr of culture, GH staining in the oocyte was absent after 24 hr of culture in 70% of COCs. Within the ovary, GH was localized in antral follicles larger than 2 mm and no staining was found in primordial, primary and secondary follicles or in the stroma. The intensity of the staining increased with the size of the follicles. Within the follicular wall the GH was persistently observed in granulosa cells, while theca cells were occasionally negative. GH mRNA in follicular compartments was only found in the oocyte and mural granulosa cells. No GHRH-r mRNA was found in the COCs nor in the granulosa or the stroma. In conclusion, the gradual increase of GH staining during follicular development and the consistent synthesis of GH in oocytes and granulosa cells, suggest a paracrine and/or autocrine action for GH in bovine follicular growth and oocyte maturation. The absence of mRNA for GHRH receptor in the COCs indicates that ovarian production of GH is not regulated by GHRH.

Follicle-stimulating hormone and growth hormone act differently on nuclear maturation while both enhance developmental competence of in vitro matured bovine oocytes

This study was designed to investigate the effect of follicle-stimulating hormone (FSH) on nuclear maturation, fertilization, and early embryonic development of in-vitro-matured bovine oocytes and to find out whether this effect is exerted through a cyclic adenosine monophosphate (cAMP) signal transduction pathway. In addition the effect of the combination of FSH and growth hormone (GH) on subsequent cleavage and embryo development was studied. Therefore cumulus oocyte complexes were cultured in the presence of FSH (0.05 IU/ml) and the nuclear stage of the oocytes was assessed using 4,6-diamino-2-phenyl-indole (DAPI) staining either after 16, 20, or 24 hr of in vitro maturation or 18 hr after the onset of fertilization. To assess the effect of FSH and the combination of FSH and GH added during in vitro maturation on the developmental capacity of the oocytes, cumulus oocyte complexes were incubated in the presence of either FSH (0.05 IU/ml) or FSH (0.05 IU/ml) plus GH (100 ng/ml) for 22 hr, followed by in vitro fertilization and in vitro embryo culture. To investigate whether FSH-induced oocyte maturation is exerted through the cAMP pathway, cumulus oocyte complexes were cultured in M199 supplemented with FSH (0.05 IU/ml) and H-89 (10 microM), a specific inhibitor of cAMP-dependent protein kinase A. After 16 hr of culture, the proportion of oocytes in metaphase II (MII) stage was determined. Cultures with GH and without FSH and H-89 served as controls. The percentage of MII oocytes at 16 hr of incubation was significantly lower (P < 0.001) in the presence of FSH than in the control group, while the number of MII oocytes beyond 20 hr did not differ from the control group. That points to a transient inhibition of nuclear maturation by FSH. Opposite to FSH, addition of GH during in vitro maturation significantly enhanced the number of MII oocytes after 16 hr of culture (P < 0.001), which points to the acceleration of nuclear maturation by GH. Addition of FSH during in vitro maturation significantly enhanced the proportion of normal fertilized oocytes, cleaved embryos and blastocysts (P < 0.001). Similarly, addition of GH during in vitro maturation significantly enhanced the number of cleaved embryos and blastocysts (P < 0.001); however, in vitro maturation in the presence of GH and FSH did not result in an extra enhancement of the embryo development. Both the inhibition of nuclear maturation by FSH and its acceleration by GH was completely abolished by H-89. In conclusion, in vitro maturation of bovine oocytes in the presence of FSH retards nuclear maturation via a cAMP-mediated pathway, while it enhances fertilizability and developmental ability of the oocytes. Supplementation of GH and FSH during in vitro maturation did not result in an extra increase in the number of blastocysts following in vitro fertilization and in vitro embryo culture.

Effects of long-term treatment with bovine somatotropin on follicular dynamics and subsequent oocyte and blastocyst yield in an OPU-IVF program

Fourteen Holstein-Friesian heifers between 15 and 22 months of age with normal reproductive tracts were used in an experimental set up to investigate the effect of a long term rBST-treatment on the follicular population prior to transvaginal ovum pick-up (OPU). The estrous cycle of the animals was synchronized by means of a double injection of 2 ml cloprostenol 11 days apart. The heifers were divided in 2 equal groups (n = 7) in which the animals had the same average body weight, one group receiving a weekly subcutaneous injection of 640 mg recombinantly derived bovine somatotropin (rBST) on Mondays (rBST-treatment group) and a control group, being injected with 10 ml of saline. Heifers in both groups were submitted to OPU twice a week on Mondays and Thursdays using a 5 Mhz transducer and a disposable, 55 mm long, 20-g short bevelled needle at a vacuum pressure corresponding to approximately 13 ml water/min. The experimental period lasted for 10 weeks (April to June), each animal receiving a total of 10 injections and being submitted to OPU for 20 times. Oocytes were subsequently matured and cultured in a separate drop per cow following conventional IVF procedures. A blood sample was taken on heparin immediately after each OPU session, for determination of blood progesterone concentrations to assess the influence of treatment and OPU procedure on the cow's estrous cycle. Although results show a significant increase in the total number of follicles and medium sized follicles in the rBST-treated group, no statistically significant different number of retrieved oocytes between the rBST-treated and nontreated group could be detected. The average number of retrieved oocytes per session per cow was comparable, being 6.4 for the treated and 6.0 for the control group. Additionally, the average number of blastocysts per cow per session did not differ significantly between groups, being 1.41 in the rBST-treated group and 1.53 in the control group. The number of cultured oocytes which developed to the blastocyst stage was 22% in the rBST-treated group, which was not significantly different from 25% in the control group. Repeated OPU appeared to induce a certain degree of acyclicity in both treated and nontreated animals.

Stimulatory effect of growth hormone on in vitro maturation of bovine oocytes is exerted through cumulus cells and not mediated by IGF-I

A previous study reported that the addition of bovine growth hormone (bGH) during in vitro maturation of bovine oocytes accelerates nuclear maturation and stimulates subsequent embryonic development. The aim of this study was to investigate whether bovine cumulus oocyte complexes (COCs) contain growth hormone receptor (GHR), and whether the stimulatory effect of GH on oocyte maturation is cumulus-dependent and mediated by insulin-like-growth factor (IGF-I). The expression of growth hormone receptor mRNA in mural granulosa cells, in cumulus cells, and in the oocyte was studied using reverse transcriptase polymerase chain reaction (RT-PCR). To investigate the importance of cumulus cells for GH-promoted maturation, COCs and denuded oocytes were cultured for 16 hr in M199 with or without bGH s(NIH-GH-B18). To investigate whether GH action is mediated by IGF-I, COCs were cultured in 1) 100 ng/ml bGH, 2) 100 ng/ml bGH plus anti-IGF-I, 1:100 dilution, 3) 100 ng/ml h-IGF-I, 4) 100 ng/ml h-IGF-I plus anti-IGF-I, 1:100 dilution, and 5) anti-IGF-I, 1:100 dilution. Culture was performed at 39 degrees C in a humidified atmosphere with 5% CO2 in air, and the nuclear stage of oocytes was assessed using 4,6-diamino-2-phenyl-indole (DAPI) staining. PCR on cDNA of mural granulosa cells, cumulus cells, and oocytes revealed that mRNA for GHR was present in all cell types. Addition of GH (100 ng/ml) to the culture medium of denuded oocytes did not affect the number of metaphase II oocytes after 16 hr, while a significant (P < 0.001) increase was observed, when COCs were cultured in the presence of GH. Addition of the antibody against IGF-I to the culture medium completely suppressed the stimulatory effect of IGF-I on oocyte maturation and cumulus expansion, while stimulation by GH was not affected by the antibody. It is concluded that bovine cumulus cells, mural granulosa, and oocytes express mRNA for the GH receptor. The stimulatory effect of GH on bovine oocyte maturation is dependent on the cumulus cells and is not mediated by IGF-I.

In vitro maturation of bovine oocytes in the presence of growth hormone accelerates nuclear maturation and promotes subsequent embryonic development

Regulatory effect of GH on follicular growth and development in the cow is well documented. The aim of this study was to investigate the role of GH on in vitro bovine oocyte maturation. Therefore bovine cumulus oocyte complexes (COCs) were cultured in M199 without FCS and gonadotropins and in the presence of 10, 100, or 1,000 ng/ml bovine GH (NIH-GH-B18). The COCs were incubated at 39 degrees C in a humidified atmosphere with 5% CO2 in air and nuclear stage was assessed after 2, 4, 8, 16, 22, and 24 hr of incubation using DAPI staining. To assess the effect of GH on developmental capacity of the oocytes, COCs were incubated in the presence of GH for 22 hr, followed by IVF and in vitro embryo culture. Cultures without GH served as controls. For subsequent development, the embryos were cultured in M199 supplemented with 10% FCS on a monolayer of BRL cells. Embryos were scored morphologically and the efficiency of the culture system was evaluated as (1) the percentage of cleaved embryos 4 days after IVF, (2) the percentage of blastocysts on day 9 expressed on the basis of the number of oocytes at the onset of culture, and (3) the percentage of hatched blastocysts on day 11 expressed on the basis of the total number of blastocysts present at day 9. GH (100 and 1,000 ng/ml) significantly accelerated nuclear maturation (P < 0.001). At 4 and 8 h the percentage of oocytes in GV stage after GH treatment (54% and 19%) was significantly lower than the control (64% and 41%). Similarly at 16 and 22 h the percentage of oocytes in MII stage was significantly higher in the GH-treated group; (58% and 77%) and (46% and 62%) for GH and control respectively. The number of oocytes in MII beyond 22 hr of culture did not differ; 100 and 1,000 ng/ml GH induced significant cumulus expansion (P < 0.05), which was not observed in the absence of GH. Addition of 100 and 1,000 ng/ml GH during maturation significantly (P < 0.01) enhanced subsequent cleavage rate from (64% and 67%) in control to (75% and 81%) in GH-treated group; embryonic development in terms of day 9 blastocyst formation was also significantly increased in the presence of GH (29% and 34%) compared to the control (18% and 24%). The hatchability of the blastocysts was not influenced by GH. From the present data, it can be concluded that GH present during IVM has a beneficial effect on subsequent development.

Pretreatment with recombinant bovine somatotropin enhances the superovulatory response to FSH in heifers

One of the primary limiting factors to superovulation and embryo transfer in cattle has been the large variability in response, both between and within animals. It appears that the primary source of this problem is the variability in the population of gonadotropin-responsive follicles present in ovaries at the time of stimulation. We have shown that treatment of heifers with recombinant bovine somatotropin (rbGH) increases the number of small antral follicles (2 to 5 mm) and, therefore, enhances the subsequent superovulatory response to eCG. To investigate further the potential of using this approach to improve superovulatory regimens in cattle, the effect of rbGH pretreatment on the response to pituitary FSH was studied. The estrous cycles of 16 heifers were synchronized using PGF2alpha. On Day 7 of the synchronized cycle, half of the animals were injected with 320 mg sustained-release formulated rbGH, while the other half received 10 ml saline. Five days later, all heifers were given a decreasing-dose regimen of twice daily injections of oFSH for 4 d, incorporating an injection of PGF2alpha with the fifth FSH treatment, to induce superovulation. All animals were artificially inseminated twice with semen from the same bull during estrus. Ova/embryos were recovered nonsurgically on Days 6 to 8 of the following estrous cycle, and the ovulation rate assessed on Day 9 by laparoscopy. Using the same animals as described above, the experiment was repeated twice, 3 and 6 mo later, with no laparoscopy in the third experiment. The animals were randomized both between experiments and for the day of ova/embryo collection. Pretreatment of heifers with rbGH significantly (P < 0.01) increased the number of ovulations, total number of ova/embryos recovered and the number of transferable embryos. The percentage of transferable embryos was significantly (P < 0.05) increased by rbGH pretreatment. In addition, the incidence (2/16) of follicular cysts with a poor ovulatory response (< 6 ovulations) for the rbGH-pretreated heifers was significantly lower (P < 0.05) when compared with the incidence (7/16) in the control animals. It is concluded that pretreatment with rbGH may provide a useful approach for improving superovulatory response in cattle.