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T R Hansen

Publications and source records attributed to T R Hansen.

At least 55 records · Page 3Linked to original sources
PubMed1991

The genes for the trophoblast interferons and the related interferon-alpha II possess distinct 5'-promoter and 3'-flanking sequences.

The genes for trophoblast interferons (IFN) bovine trophoblast protein-1 (bTP-1) and ovine trophoblast protein-1 (oTP-1) are expressed massively in the trophectoderm of preimplantation bovine and ovine concepti during the period of maternal recognition of pregnancy. These 172-amino acid IFN are closely related to the IFN-alpha II, a family of "long" IFN expressed in virus-induced leukocytes. Genomic Southern blotting with a full-length bTP-1 cDNA revealed about 15 genes that bind the probe with varying intensities. By using more specific probes for the 3'-ends of the cDNA, we have shown that only four to five of these represent bTP-1 genes, whereas no more than another four are IFN-alpha II. Genes for bTP-1 and IFN-alpha II, all of which are intronless, have been isolated from bovine genomic libraries, and their nucleotide sequences were compared. Additional bTP-1 genes and two distinct oTP-1 genes have been isolated from bovine and ovine genomic DNA by using the polymerase chain reaction procedure in conjunction with specific 3'- and 5'- primers (derived from the bTP-1 gene sequences determined above). The promoter region up to 100 bases upstream from the transcription start sites of the trophoblast IFN are almost completely conserved across different genes and across species, yet show only limited sequence identity with IFN-alpha II. Two putative binding regions for interferon regulatory factor-1 as well as several GAAANN motifs (where N is any nucleotide) that have been implicated in viral responsiveness of alpha 1- and beta-IFN genes are retained at identical positions in all of the trophoblast genes. Putative interferon regulatory factor-1-binding nucleotide hexamers and GAAANN motifs are also present in the IFN-alpha II genes, but these are organized very differently than in the trophoblast IFN genes. A GAAATG motif is present in IFN-alpha II promoters but is absent in trophoblast IFN genes. Based on the evidence presented, it is proposed that the trophoblast interferons constitute a separate subclass of IFN-alpha distinct from IFN-alpha II and IFN-alpha I.

Animals↗
PubMed1991

Preoperative laboratory screening in healthy Mayo patients: cost-effective elimination of tests and unchanged outcomes.

We reviewed the results of preoperative screening laboratory tests in asymptomatic healthy patients who underwent elective surgical procedures at our institution in 1988. Substantially abnormal results were found in 160 of 3,782 patients. All such abnormalities involved five tests: aspartate aminotransferase, glucose, potassium, platelet count, and hemoglobin. Thirty of the abnormal test results were predictable on the basis of the history or physical examination. The abnormal test result prompted further assessment in 47 patients. No surgical procedure was delayed, and no association was noted between adverse outcome and any preoperative laboratory abnormality. Because of our findings in this analysis and similar studies on specific tests from other institutions, we no longer require preoperative laboratory screening tests for healthy patients.

Adult↗
PubMed1991

Slowed transcription and rapid messenger RNA turnover contribute to a decline in synthesis of ovine trophoblast protein-1 during in vitro culture.

Ovine trophoblast protein-1 (oTP-1) is produced in massive amounts by conceptuses during the Day-12-20-period of early pregnancy. The rate of production of oTP-1 declines during culture of conceptuses, however, suggesting a role for critical intrauterine factors for continued production. The present study was conducted to define the mechanism responsible for the in vitro decline in oTP-1 synthesis. Over 24 h culture, synthesis of oTP-1 was initially rapid but then declined such that there was little increase in either the protein or its antiviral activity after 12 h. By contrast, the release of total protein into the medium continued at an approximately linear rate for the entire 24-h period of culture. By using in situ hybridization to tissue sections and dot-blot analysis of tissue extracts with labeled cDNA probes, it was shown that the quantity of oTP-1 mRNA fell 3- to 5-fold during culture, whereas the amount of actin mRNA remained relatively constant. To determine whether this selective fall in levels of oTP-1 mRNA resulted from decreased transcription rate and/or high turnover rate of existing mRNA, conceptuses were either provided continuously with [3H]uridine for 24 h or labeled for 9 h and then exposed to medium enriched in unlabeled uridine and cytidine for a further 15 h. Specific incorporation of 3H into oTP-1 mRNA was assessed by hybridization to excess oTP-1 cDNA immobilized on nitrocellulose membranes. In the continuous labeling study, 3H in total RNA increased at an approximately linear rate for at least 18 h, whereas the content of 3H in oTP-1 mRNA peaked at 9 h and declined about 10-fold by 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The polypeptides and genes for ovine and bovine trophoblast protein-1.

Ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1) have been strongly implicated as antiluteolytic agents and responsible for maternal recognition of pregnancy in sheep and cattle, respectively. Both are interferons (IFN) belonging to the IFN-alpha family, but their length (172 residues versus 166 for most IFN-alpha) places them in an unusual subclass (the IFN-alpha II). The various isoforms of oTP-1 and bTP-1 produced by trophoblast tissue appear to arise in part from translation of multiple mRNAs which are themselves the products of distinct genes. These genes, like those for other IFN-alpha, are without introns. However, the genes for oTP-1 and bTP-1 form a distinct subgroup within the IFN-alpha II on the basis of their overall primary sequences and the high conservation of the 3'-untranslated ends of their transcription units. The bTP-1 genes also differ from the bovine IFN-alpha II in the organization of the promoter regions upstream from the transcription start site. Nevertheless, computer-aided analysis of the primary polypeptide sequences of oTP-1 and bTP-1 indicates that the molecules are likely to have approximately the same shapes and dimensions as all other IFN-alpha molecules. It remains to be determined whether they have unique biological properties which distinguish them from other IFN-alpha molecules.

Amino Acid Sequence↗
PubMed1990

Expression of trophoblastic interferon genes in sheep and cattle.

The trophoblastic interferons ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1, respectively) have been implicated as mediators of maternal recognition of pregnancy in sheep and cattle. The objective of this study was to describe the onset and duration of gene expression for oTP-1 and bTP-1 in preimplantation ovine and bovine conceptuses by in situ hybridization and Northern analysis. Sections from paraffin-embedded ovine conceptuses, collected on Days 10, 11, 12, 13, and 15 of gestation (n = 1, 3, 3, 2, 2), and bovine conceptuses, collected on Days 12/13, 15/16, and 19 (n = 2, 4, 5), were hybridized to specific [35S]-labeled cDNA probes. Two different probes, one encompassing bases 442-918 and representing both coding and 3'-untranslated regions, and a second 3'-specific probe (bases 650-912) were used to detect oTP-1 mRNA. At all stages examined, oTP-1 mRNA was confined to trophectoderm of ovine conceptuses. Consistent with earlier studies, expression increased markedly at Day 13. oTP-1 mRNA was detected at low levels in seven of seven ovine conceptuses prior to Day 13 when the longer probe was employed. With the 3'-specific probe, however, oTP-1 mRNA was detected in only one of the seven ovine conceptuses prior to Day 13. Thus, although low amounts of oTP-1 mRNA may be present in ovine conceptuses prior to Day 13, massive induction of this mRNA occurs on Day 13 coincident with the initiation of maternal recognition of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1990

Interferons at the placental interface.

The antiluteolytic factors secreted by sheep and cattle conceptuses are closely related structurally to alpha-interferons (IFN-alpha s). They are known as ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1), respectively. The mRNAs for oTP-1 and bTP-1 are transcribed from multiple genes and are the major translatable messages of Day 13-17 sheep conceptuses and Day 15-20 cattle conceptuses. The proteins belong to the 172-amino acid IFN-alpha II (or IFN-omega) subfamily and have the typical antiviral and antiproliferative properties of the 166-residue IFN-alpha Is. These embryonic interferons also bind to the IFN-alpha receptor, which is present in uterine endometrium in high concentrations, and can influence the production of prostaglandin F-2 alpha and the pattern of protein secretion in that tissue. Through use of in-situ hybridization procedures on tissue sections and Northern and dot blot analyses of extracted conceptus RNA, ovine oTP-1 mRNA has been shown to increase markedly around Day 13 and to decrease after about Day 15 of pregnancy. The mRNA is confined entirely to cells of the trophectoderm. Significant induction of mRNA that hybridizes to an oTP-1 cDNA occurs in response to exposure to polyI:polyC in Day 11 sheep blastocysts which normally have low levels of oTP-1 expression. However, the basis for induction in the normal progression of embryonic development remains unclear. The fact that preimplantation conceptuses of other species, e.g. pig, release substances with antiviral activity suggests that IFNs may have an important role in pregnancy that extends beyond the domestic ruminants.

Amino Acid Sequence↗
PubMed1989

Interferon production by the preimplantation sheep embryo.

Ovine trophoblast protein-1 (oTP-1), the major product secreted by the trophectoderm of the sheep conceptus between days 13 and 21 of pregnancy, is considered to mediate maternal recognition of pregnancy by maintaining the function of the corpus luteum. Its amino acid sequence has 40-55% identity with various mammalian interferons-alpha (IFN-alpha), and it has been shown to have antiviral activity. The present results confirm that oTP-1, which at days 15-17 of pregnancy is produced by a single embryo at more than 100 micrograms (greater than 1 million antiviral units) per day, is a functional IFN. A preparation of purified oTP-1 was made. Its amino-terminal sequence suggested that it consisted of a single homogeneous protein, so that its antiviral activity probably was not due to a contaminant. In a cytopathic effect inhibition assay with GBK-2 bovine cells challenged with vesicular stomatitis, its specific activity was 1.3 X 10(7) end point units/mg protein. It also protected GBK-2 cells against four other viruses, and A549 human cells against encephalomyocarditis virus. The antiviral activity was neutralized by an antiserum to human leukocyte IFN. Like human IFN-alpha, oTP-1 at concentrations as low as 10(-9) M inhibited the growth of GBK cells in culture and suppressed mitogen-stimulated incorporation of [3H]thymidine into ovine lymphocytes. Possible roles for oTP-1, functioning as an IFN-alpha during early pregnancy, are discussed.

Age Factors↗
PubMed1989

Complex binding of the embryonic interferon, ovine trophoblast protein-1, to endometrial receptors.

Ovine embryos produce an interferon (IFN)-alpha II in significant quantities during early pregnancy. This IFN, previously termed ovine trophoblast protein-1 (oTP-1), is a 172-amino-acid polypeptide which has been suggested to be the causal agent in maternal recognition of pregnancy in the ewe. Here we report the binding of oTP-1 and a recombinant bovine IFN-alpha I1 (rBoIFN-alpha I1; 165-166 amino acids long) to membrane preparations from ovine uterine endometrium. Both oTP-1 and rBoIFN-alpha I1 competed with each other for receptor binding. Based on Scatchard analysis, [125I]oTP-1 binding was determined to be complex and resolvable into a high-affinity (Kd = 3.8 x 10(-11) M, 30 fmoles/mg protein) and a low affinity (Kd = 1.7 x 10(-10) M; 96 fmoles/mg protein) component. Conversely [125I]rBoIFN-alpha I1 bound to only a single high-affinity receptor (Kd = 6.1 x 10(-11) M; 174 fmoles/mg protein). Cross-linking experiments using disuccinimidyl suberate revealed that [125I]oTP-1 associated with membrane polypeptides of two molecular weight classes (Mr 100,000 and 70,000), and could be displaced from both with rBoIFN-alpha I1. In contrast, [125I]rBoIFN-alpha I1 cross-linked to only the 100,000 Mr membrane polypeptide. These data provide evidence that the binding parameters of oTP-1 and rBoIFN-alpha I1 to endometrial receptors are different.

Animals↗
PubMed1989

Suppression of T-lymphocyte blastogenesis by ovine trophoblast protein-1 and human interferon-alpha may be independent of interleukin-2 production.

Cells derived from the trophoblast tissue of a day 15 sheep conceptus released substances that inhibit incorporation of [3H]thymidine into phytohemagglutinin (PHA)-stimulated ovine lymphocytes. This effect was partially reversed by addition of antiserum to ovine trophoblast protein-1 (oTP-1), a major secretory product of day 13-21 sheep conceptuses and a protein structurally and functionally related to alpha-interferons (IFN-alpha). Human IFN-alpha, unlike dexamethasone, inhibits phytohemagglutinin-induced lymphocyte blastogenesis without reducing interleukin-2 (IL-2) production by the cultures, and conditioned medium containing IL-2 does not promote [3H]thymidine incorporation into ovine lymphocytes when oTP-1 is present. Thus, oTP-1, by virtue of being an IFN, may have a local immunomodulatory role by selectively inhibiting the proliferative responses of certain maternal immune cells to IL-2.

Animals↗
PubMed1989

Molecular cloning and characterization of complementary deoxyribonucleic acids corresponding to bovine trophoblast protein-1: a comparison with ovine trophoblast protein-1 and bovine interferon-alpha II.

Bovine trophoblast protein-1 (bTP-1) is a secreted glycoprotein that consists of several forms differing slightly in mol wt and isoelectric point. It is produced by bovine conceptuses after about day 15 of pregnancy and is believed to play a key role in signalling the presence of an embryo to the mother. In this study, a series of recombinant cDNA clones corresponding to the mRNA for bTP-1 have been isolated from cDNA libraries representing day 18-19 bovine conceptus poly(A)+ mRNA. Base sequencing of several cDNAs indicated that multiple mRNAs for bTP-1 exist. Northern blotting and primer extension experiments showed that the mRNAs average about 1 kilobase in length. One apparently full-length cDNA clone consisted of 1035 bases up to the beginning of the poly(A) tail. It contained an open reading frame of 195 codons which began at a position 79 bases from the 5' end. Its entire sequence was 85% identical to that of a cDNA for the immunologically related ovine trophoblast protein-1 (oTP-1) and about 79% identical to that for a bovine interferon-alpha II (IFN alpha II). The highest conservation of sequence (greater than 90%) was noted in the 3'-untranslated sequences of the bTP-1 and oTP-1 cDNAs. The deduced amino acid sequence of bTP-1 shared 80% identity with oTP-1, between 45-55% with human, rodent, porcine, and bovine IFNs of the alpha 1 subfamily and about 70% with a bovine IFN alpha II. A single potential site for N-glycosylation was noted at Asn78. These results show that bTP-1, like its ovine counterpart oTP-1, is structurally related to the IFN alpha S. We suggest that these embryonic IFNs play a role in controlling immunoreactions at the trophoblast-uterus interface as well as triggering other maternal responses to pregnancy.

Amino Acid Sequence↗
PubMed1988

Interferon RNA of embryonic origin is expressed transiently during early pregnancy in the ewe.

Ovine trophoblast protein-1 (oTP-1), an interferon of embryonic origin, is produced during the peri-implantation period of early pregnancy. Secretion of oTP-1 is detectable between days 13 and 21, but not beyond. In this study, the levels of oTP-1 mRNA in embryos were analyzed to determine if they reflected the transient nature of oTP-1 production. Total cellular RNA (tcRNA) was isolated from embryos representing day 12 (n = 5), 14 (n = 7), 16 (n = 5), 18 (n = 6), 20 (n = 4), and 22 (n = 5) of pregnancy and spotted on nylon membranes. Complementary RNA was transcribed from a specific oTP-1 cDNA (550 base pairs) template and applied (16-1000 pg) to nylon membranes to develop a standard curve. The fixed RNA samples were then allowed to hybridize with the 32P-labeled oTP-1 cDNA. oTP-1 mRNA was not detectable on day 12, increased to high levels (3.6 +/- 1.6 ng/ug of embryo DNA) on day 14, decreased about 5-fold by day 16, 15-fold by day 18, 170-fold by day 20, and 200-fold by day 22 of pregnancy. At day 14 oTP-1 mRNA comprised 0.060 +/- 0.019% of the tcRNA and was more abundant than actin mRNA. Northern analyses of pooled tcRNA representing each day of pregnancy showed that the oTP-1 probe hybridized to a single class of mRNA (approximately 1.1 kilobases) and confirmed the results obtained with dot blots.

Actins↗
PubMed1988

Granulosa cell steroidogenesis and follicular fluid steroid concentrations after the onset of oestrus in cows.

Granulosa cell responsiveness at an early (1-2 h) or late (14-16 h) stage of differentiation following the onset of oestrus [and presumably the LH surge] was studied in 16 cows. Follicular fluid collected at the early stage (8 preovulatory follicles) had a higher concentration of testosterone (P less than 0.05), oestradiol (P less than 0.01) and oestrone (P less than 0.01) than did follicular fluid collected at the late stage of oestrus (8 preovulatory follicles). No difference in follicular fluid progesterone was noted between follicles collected at the early and late stages of oestrus. Granulosa cells collected at the early stage of oestrus had a higher in-vitro response (progesterone production) to LH (P less than 0.05), forskolin (P less than 0.08) and diacylglycerol (P less than 0.05) than did granulosa cells collected at the late stage of oestrus. However, later stage granulosa cells produced more (P less than 0.01) progesterone after culture with prostaglandin E-2 than did earlier stage granulosa cells. These results show that follicular fluid oestrogen decreases, which suggests a loss of aromatase activity as oestrus progresses, and that granulosa cells become refractory (low progesterone production) to in-vitro LH, forskolin, and diacylglycerol challenge, yet acquire responsiveness to prostaglandin E-2 as oestrus progresses.

Animals↗
PubMed1987

Bovine corpus luteum regression and estrous response following treatment with alfaprostol.

Two trials evaluated bovine corpus luteum (CL) regression and estrous response following treatment with alfaprostol (AP), a prostaglandin F2 alpha analogue. Expression of at least one estrous cycle (16 to 26 d) and a palpable mid-cycle CL were required prior to random assignment of females to receive 0, .38, .75, 1.50 or 2.25 mg AP/100 kg body weight. Alfaprostol was evaluated in Brahman cows and heifers that were treated on d 11 to 13 (trial 1) and in Simmental X Brahman-Hereford (crossbred) heifers that were treated on d 8 to 10 or d 11 to 13 of the estrous cycle (trial 2). In trial 1, Brahman heifers appeared to require a higher AP dose (greater than .38 mg/100 kg body weight) to elicit luteolysis and expression of estrus than Brahman cows. Alfaprostol treatment (greater than or equal to .75 mg/100 kg body weight) induced (P less than .0001) luteolysis followed by estrus in Brahman cows and heifers. In trial 2, crossbred heifers that received AP on d 8 to 10 appeared to require a higher dose of AP (greater than .38 mg/100 kg body weight) to elicit luteolysis and estrus than heifers that received AP on d 11 to 13 of the estrous cycle. Alfaprostol treatment greater than or equal to .75 mg/100 kg body weight on d 8 to 10 and d 11 to 13 of the estrous cycle induced (P less than .0001) luteolysis followed by estrus in crossbred heifers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Corpus luteum function following spontaneous or prostaglandin-induced estrus in Brahman cows and heifers.

Corpus luteum (CL) function following spontaneous or prostaglandin F2 alpha-induced estrus was studied in 27 Brahman cows and 16 Brahman heifers. Females received one injection of 0, .38, .75 or 2.25 mg alfaprostol (PGF)/100 kg body weight at 12 +/- .1 d post-estrus. Serum progesterone (P4) during CL formation, following the subsequent estrus, increased over time (P less than .001, 1 to 13 d post-estrus) and was influenced by PGF (P less than .06) and a PGF X time interaction (P less than .02). Low serum P4 concentrations were observed during CL formation (d 3, 4, 10, and 12) in cattle that received 2.25 mg PGF. On d 13 post-estrus, CL were removed. No differences in weight, P4 content or number of luteinizing hormone (LH) receptors was evident between CL derived 13 d following spontaneous vs PGF-induced estrus. The CL formed following PGF-induced estrus had fewer large (P less than .002) and small (P less than .09) luteal cells in heifers, a lower (P less than .008) percentage composition of histological type I and II luteal cells in cows and a lower (P less than .0001) in vitro P4 response to LH in both cows and heifers when compared with the CL formed following spontaneous estrus. Cows had heavier (P less than .002) CL with a higher (P less than .05) number of large cells, a higher (P less than .09) percentage composition of histological cell type I and II luteal cells, and a higher (P less than .03) in vitro basal and stimulated P4 secretion. It is concluded that 1) the events associated with artificially shortening the estrous cycle with PGF altered subsequent CL function in Brahman females; 2) cows had heavier CL, which were composed of more steroidogenically functional luteal cells, than heifers and 3) age of animal interacted with PGF to alter subsequent CL function in Brahman females.

Animals↗
PubMed1984

Mechanism of action of barium ion on rat aortic smooth muscle.

The mechanism of action of barium ion on the aortic smooth muscle of the normal rat was investigated using in vitro calcium-depleted aortic strips. Aortic strips were depleted of calcium by repeated exposure to norepinephrine in a calcium-free bathing solution. Although calcium depletion abrogated the response of strips to catecholamines and depolarizing agents, the response to barium chloride remained quantitatively intact. The calcium influx blocker D 600 prevented the contractile response to barium but not to catecholamines, whereas phentolamine prevented the response to catecholamines but not barium. The strip response to barium was depressed by a twofold increase in extracellular magnesium concentration whether the strip was intact or calcium depleted. Although increased concentrations of calcium in the extracellular medium inhibited the contractile response to potassium ion, increases in barium merely potentiated the potassium contracture. These findings indicate that barium produces its contractile effect on vascular smooth muscle by a direct intracellular interaction with the contractile or regulatory proteins. Barium enters these cells via calcium influx channels and is probably not sequestered in a physiologically releasable pool. Unlike calcium, barium does not stabilize the smooth muscle sarcolemma when present in high concentration.

Animals↗
PubMed1984

Ovarian and uterine morphology and function in Angus and Brahman cows.

Ovarian characteristics, daily serum progesterone (P4) and estradiol-17 beta (E2) concentrations (d 7 through 17) and uterine luminal secretory protein components and histological variables were evaluated in parous Bos taurus (Angus, n = 20) and Bos indicus (Brahman, n = 19) cows. Cows were slaughtered on d 17 (estrus = d 0) for measurement of ovarian structures, flushing of uteri and removal of uterine tissue for histological evaluation. Cows were placed into one of three reproductive categories: nonpregnant, remnant (flushings contained remnants of embryonic tissue) or pregnant. For ovarian and uterine variables, there were only a few differences among reproductive categories within breeds. For combined categories, weight of the active ovary (containing the corpus luteum) was similar between breeds, but inactive ovarian (P less than .001) and follicular fluid (P less than .01) weights, stromal weight (P less than .01) and number of follicles less than 5 mm in diameter (P less than .01) for both ovaries combined were greater in Brahman than Angus cows. Corpus luteum weight (P less than .001), luteal P4 content (P less than .08) and number of follicles greater than 5 mm in diameter for both ovaries combined (P less than .05) were greater for Angus than for Brahman cows. Overall, mean serum P4 concentrations were greater in nonpregnant (P less than .05), pregnant (P less than .005) and combined (P less than .025) reproductive categories for Angus than corresponding categories of Brahman cows and mean serum E2 concentrations were greater in remnant (P less than .025) and combined (P less than .05) reproductive categories for Angus than corresponding categories of Brahman cows. Mean total uterine luminal protein was greater (P less than .05) in Angus than in Brahman cows for pregnant (23.4 vs 14.7 mg, respectively) and combined reproductive categories (22.4 vs 16.1 mg, respectively). Using electrophoretic analyses, percentage composition of three uterine specific cathode migrating protein bands and quantitative estimates of proteins with molecular weights (MW, X 10(-3)) of 9, 15.5, 34.2, 41.3, 46.2 and 183.1 were greater (P less than .05 to P less than .001) in uterine flushings from Angus than from Brahman cows. Uterine, myometrial and endometrial thicknesses, number of glands/microscopic field and uterine luminal epithelial cell height variables were generally greater (P less than .05 to P less than .001) in pregnant and combined reproductive categories for Angus than for Brahman cows.

Animals↗
PubMed1982

Evidence for seasonal and nutritional modification of ovarian and pituitary function in crossbred heifers and Brahman cows.

Alterations in endocrine response in the bovine female after consumption of monensin or exposure to changes in season were observed in two experiments. Thirty-three monensin-fed (M) or control (C) crossbred heifers in Exp. 1A were given a porcine follicle stimulating hormone (FSH-P) challenge on d 16 to 21 postestrus. Nine M heifers ovariectomized (OVX) on d 11 after the FSH-challenged estrus had a greater number of smaller corpora lutea (CL; P less than .005) than did nine d 11 OVX C heifers. Serum progesterone (P4) concentrations were greater in M on d 5 through 13 following the FSH-challenged estrus (P less than .001). Seven M and seven C Brahman cows in Exp. 1B given an identical FSH challenge had similar increases in CL number and size. In Exp. 2, blood samples were obtained from 14 M and 13 C Brahman cows during winter (WI), early spring (ESp) and late spring (LSp) to characterize the preovulatory LH surge. During each seasonal period, blood samples were taken hourly from estrus through 24 h postestrus for each cow. Only one of five WI-C cows had a preovulatory LH surge compared to five of five WI-M cows (P less than .01). No differences were found in the number of cows having an LH surge in ESp or LSp groups. Analysis of combined WI and ESp group values indicated a difference in timing of the LH surge by M or C treatment. Of those cows that had an LH surge, only three of 10 C had peak LH values later than the first sample taken, compared with 10 of 15 M (P less than .10). A heightened LH response was detected in M cows in all comparisons of LH surge profiles (P less than .005). Concurrent with changes in season from WI to ESp was an increase in number of C cows having an LH surge (one of five vs nine of 10; P less than .005), and elevated LH values in ESp-C and M groups compared with WI-C and M groups (P less than .05). Midluteal blood samples taken after every estrus indicated P4 to be greatest in February M cows (P less than .10) and P4 tended to be greater in February and lower in January for all groups. Conclusions are that monensin affects the FSH-P-induced ovulation rate of bovine females of all ages. Seasonal effects occurring between the shortest and longest days of the year exert their greatest influence on the preovulatory LH surge and P4 concentrations in Brahman cows between January and March. Seasonal effects appear to be partially modulated by nutritional factors.

Animals↗