Michael J. Fields

Morphological characteristics of the bovine corpus luteum during the estrous cycle and pregnancy

The corpus luteum, one of the biological clocks of the estrous cycle and pregnancy, is known foremost for its production of progesterone that blocks the pituitary release of gonadotropins and prepares the uterus for a pregnancy. The cellular sources of this progesterone are the steroidogenic small and large luteal cells. Other luteal cells that are not steroidogenic, but are believed to have an important role in the function of this gland are the fibroblast, macrophages and endothelial cells. The most prominent luteal cell is the large steroidogenic cell characterized by an abundance of smooth endoplasmic reticulum and densely packed spherical mitochondria that are indicative of its contribution to most of the circulating progesterone believed to be constitutively secreted and not under the control of LH. Other distinguishing features of the large luteal cell are the presence of rough endoplasmic reticulum, prominent Golgi, and secretory granules that are indicative of endocrine cells. This cell undergoes dynamic changes across the estrous cycle and pregnancy, believed to reflect a change in progesterone and protein secretion that will eventually influence a successful pregnancy or another ovulation if pregnancy fails. The morphological characteristics of the bovine luteal cells are the focus of this review.

Insulin is released from rat brain neuronal cells in culture.

Abstract: Depolarization of neuronal cells in primary culture from the rat brain by potassium ions in the presence of calcium or by veratridine caused a greater than threefold stimulation of release of immunoreactive insulin. HPLC of the released insulin immunoreactivity from the neuronal cultures comigrated with the two rat insulins. The depolarization‐induced release of insulin was inhibited by cycloheximide and was specific for neuronal cultures since potassium ions failed to cause the release in comparably prepared astrocytic glial cells from the rat brain. Prelabelling of neuronal cultures with [3H]leucine followed by depolarization resulted in the release of radioactivity that immunoprecipitated with insulin antibody. The release of [3H]insulin was biphasic. These observations suggest that neuronal cells from the brain have the capacity to synthesize insulin that could be released under depolarization conditions.

Ovulation triggers oxytocin gene expression in the bovine ovary.

Oxytocin Neurophysin Corpus luteum Estrous cycle Gene expression

Aspects of the sexual development of Brahman versus Angus bulls in Florida.

Postweaning growth and reproductive traits were studied in 10 Brahman and 12 Angus bulls from 8 through 20 months of age. Brahman bulls reached puberty at 15.9+/-.4 months of age, weighed 432+/-16 kg, had a scrotal circumference (SC) of 33.4+/-1.2 cm, and plasma testosterone of 3.96+/-1.03 ng/ml. Breed differences in SC averaged over the entire study were not significant. However, the breedxday interaction (BxD) (P<.01) showed that, initially, the Brahman SC was smaller than the Angus SC; however, by the end of the study, the Brahman SC was larger than the Angus. When SC was adjusted for body weight, breed differences (P<.01) and BxD (P<.01) for SC/body weight (BW) reflected the later age and heavier weight at which the Brahman bull reached puberty. Plasma testosterone differed between breeds (Angus>Brahman, P<.01) and increased at a linear (P<.01) rate with age. There was no BxD in plasma testosterone. No breed differences in sperm concentration were observed. However, other semen traits were different (P<.01), i.e., rate of forward movement, sperm motility, total abnormalities and semen volume. A BxD (P<.01) was also evident for breed differences in these semen traits. Sexual development of the Brahman bull occurred at a later chronological age and in a nonparallel pattern to that of the Angus. Between animal variation in SC within the Brahmans and differences between this study and other reports suggest that differences in SC exist for various populations of Brahman bulls and should provide opportunities for progress in selection for this trait.

Extragonadal Luteinizing Hormone Receptors in the Reproductive Tract of Domestic Animals

Abstract Binding sites for LH/hCG and/or its mRNA are found in the uterus of several species, including human, primate, pig, cow, and turkey. Activation of LH receptors around Day 15 of the estrous cycle is associated with increased prostaglandin F2α production in the bovine, porcine, and ovine uterus. Activation of uterine LH receptors is also associated with increased levels of prostaglandins in human and primate. The presence of gonadotropin receptors with a dynamic pattern in the oviduct, endometrium, myometrium, and cervix of different species provides evidence that gonadotropins play a substantial role in molecular autocrine-paracrine regulation of the estrous cycle and implantation.

Expression of the oxytocin gene in the large cells of the bovine corpus luteum

In the bovine ovary there is a delay of 4–6 days between the observed maximum of oxytocin mRNA and the peak in the luteal levels of oxytocin nonapeptide. This implies a maturation process involving components of the post‐translational processing pathway. In situ hybridization shows the oxytocin gene to be transcribed exclusively in the large cells of the corpus luteum at the beginning of the estrous cycle.

Oxytocin and vasopressin binding sites in human and bovine ovaries

Human ovarian tissue and bovine ovarian stroma and follicles bound tritiated oxytocin and tritiated arginine vasopressin with similar affinity, whereas bovine corpora lutea bound tritiated oxytocin only. Competition for the binding of tritiated oxytocin by various agonists and antagonists was suggestive of receptor function. The number of oxytocin binding sites varied cyclically in all tissues. In bovine ovarian stroma and corpora lutea the concentrations were lowest on day 14 and highest on days 17, 19, and 21 after ovulation, with a striking peak in the luteal concentration on day 19. In human ovarian tissues the concentrations also were highest in samples obtained in late luteal phase. In large follicles the concentration of oxytocin binding sites was highest on the day of estrus and lowest on day 7. In bovine ovary the number of arginine vasopressin binding sites was approximately 50% lower than oxytocin binding sites and the cyclic variations were not significant. Human ovarian tissue had similar numbers of oxytocin and arginine vasopressin binding sites. Because bovine ovaries produce oxytocin and arginine vasopressin the results suggest a paracrine or autocrine role for these neuropeptides in luteolysis and ovulation. Although their synthesis in human ovaries is still controversial the presence of binding sites suggests a physiologic role in the regulation of human ovarian function as well.

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): I. Fertility.

Two trials were conducted over a two-year period with 519 cycling Bos taurus x Bos indicus heifers and cows. The objectives of these trials were: 1) To compare fertility of artificial insemination at the cloprostenol-induced estrus and the naturally occurring estrus, 2) To evaluate the fertility of artificial insemination at a predetermined time (Timed AI) following an estrous synchronization regime with cloprostenol (CLP) and 3) To define the optimum interval from a second CLP treatment for Timed AI. In Trial I, 128 animals were assigned to four treatments: 1) Controls, which were inseminated at the natural occurring estrus; 2) timed AI at 72 hr and again at 96 hr post-second CLP; 3) Timed AI at 72 hr post-second CLP and 4) AI at the CLP-induced estrus. Trial II included 391 heifers distributed among six treatments; 1) Timed AI between 70 and 90 hr post-second CLP; 2) Sham AI between 70 and 90 hr post-second CLP, 3) Chute Stress between 70 and 90 hr post-second CLP; 4) AI at the CLP-induced estrus; 5) Control-AI at the naturally occurring estrus and 6) Non-treated and exposed to fertile bulls. The fertility of the animals artificially inseminated at the CLP-induced estrus was similar to that of insemination at the naturally occurring estrus in Trial I and Trial II (30 vs 46%; 37 vs 38%, respectively). The first service pregnancy rates of the animals bred at a predetermined time were similar to those bred at the CLP-induced estrus in Trial I, but lower in Trial II (P<.01).

Factors affecting calf crop : biotechnology of reproduction

Developments in Reproductive Biotechnology that will Improve the Weaned Calf Crop, R. Collier Bovine Estrus: Tools for Detection and Understanding, D.O. Rae An Array of Approaches to Synchronize Estrus with Prostaglandins, J.W. Lauderdale Estrous Synchronization of Cyclic and Anestrous Cows with SYNCRO-MATE-B(R), W.E. Beal Use of GnRH to Synchronize Estrus and (or) Ovulation in Beef Cows with or without Timed Insemination, J.S. Stevenson Current and Emerging Methods to Synchronize Estrus with Melengestrol Acetate (MGA), D.J. Patterson, S.L. Wood, F.N. Kojima, M.F. Smith A Vaginal Insert (CIDR) to Synchronize Estrus and Timed AI, J.V. Yelich Management of Follicular Growth with Progesterone and Estradiol within Progestin-Based Estrous Synchrony Systems, M.L. Day and C.R. Burke The Freezing, Thawing, and Transfer of Cattle Embryos, J.F. Hasler Application of Embryo Transfer to the Beef Cattle Industry, W.E. Beal Embryo Transfer in Tropically Adapted Cattle in the Semitropics, C.C. Chase, Jr. In Vitro Fertilization to Improve Cattle Production, J.J. Rutledge National Bovine Genomics Projects: Present Status, Future Directions, and Why They are Important, R.M. Roberts Genetic Technologies in Cow-Calf Operations, S.K. De Nise and J.F. Medrano Somatic Cell Cloning in the Beef Industry, A. Spell and J.M. Robl Alternative Methods to Micromanipulation for Producing Transgenic Cattle, M. Shemesh, M. Gurevich, E. Harel-Markowitz, L, Benvenisti, L.S. Shore, Y. Stram Cloning and the Beef Cattle Industry, K. Moore Reproductive Real-Time Ultrasound Technology, G.C. Lamb Factors that Affect Embryonic Survival in the Cow: Application of Technology to Improve the Calf Crop, K. Inskeep Sexing Sperm for Beef and Dairy Cattle Breeding, G.E. Seidel, Jr. New Developments in Managing the Bull, R.L. Ax. H.E. Hawkins, S.K. DE Nise, T.R. Holm, H.M. Zhang, J.N. Oyarzo, and M.E. Bellin

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): II. Estrous response.

Data collected from two controlled breeding field trials involving 561 Bos indicusxBos taurus cows and heifers were analyzed for estrous and fertility response following a cloprostenol ICI-80, 996 (CLP) synchronization regime. Fertility data were discussed in a companion paper (1). In Trial 1, 128 animals were assigned to four treatments: 1) controls which were inseminated at the naturally occurring estrus; 2) Animals artificially inseminated at approximately 72 hr and 96 hr following a second CLP; 3) Animals artificially inseminated at approximately 72 hr following a second CLP; and 4) Animals artificially inseminated approximately 12 hr after detection of estrus post-second CLP. Trial II included 391 heifers distributed among six treatments: 1) Artificially inseminated between 70 and 90 hr post-second CLP; 2) Sham inseminated between 70 and 90 hr post-second CLP; 3) Processed with no manipulation of the genital tract between 70 and 90 hr post-second CLP; 4) Artificially inseminated approximately 12 hr after the detection of estrus following a second CLP; 5) Artificially inseminated at the naturally occurring estrus and 6) Non-treated heifers exposed to fertile bulls. Cloprostenol ICI-80996 was effective (P<.01) in synchronizing estrus in comparisons of treated vs non-treated controls in Trials I and II (82 vs 29%; 57 vs 19%, respectively). However, a significant reduction in the expression of estrus was observed following Timed AI when compared to heifers bred 12 hr after detection of CLP-induced estrus in Trial II (37 vs 54%, P<.05). The authors conclude that a single timed insemination of Brahman crossbred heifers suppresses the behavioral expression of estrus. Other evidence (1) indicates that the fertility during this period is similarly reduced.