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Biomedical subjects

R D Randel

Publications and source records attributed to R D Randel.

At least 145 records · Page 8Linked to original sources
PubMed1980

The effect of dietary monensin on th luteinizing hormone response of prepuberal heifers given a multiple gonadotropin-releasing hormone challenge.

Ten prepuberal Simmental X Brahman-Hereford heifers (average weight 208 +/- 4 kg) were randomly assigned to receive either 2.7 kg/head/day of ground milo containing 0 mg monensin sodium (C) or 2.7 kg/head/day of ground milo containing 200 mg monensin sodium (M). Both groups of animals (n = 5) received Coastal bermudagrass hay ad libitum throughout the trial. On day 21 of the feeding period all heifers were fitted with jugular cannulas. Immediately after cannulation, the heifers were injected IM with 100 microgram of gonadotropin-releasing hormone (GnRH) and blood was collected every 10 min for 4 hours. Four hours after the first GnRH challenge, a second 100-microgram GnRH injection was administered, and blood samples were collected at 10-min intervals for an additional 5 hours. Serum was stored at -20 C until radioimmunoassayed for luteinizing hormone (LH). The amount of LH released after each GnRH injection was greater in the heifers fed M than in the controls (P less than .05). Peak LH after the first GnRH challenge was greater (P less than .05) in heifers fed M than in controls. The area under th first GnRH induced LH curve tended (P less than .20) to be greater for the M group than for the controls. Peak LH concentration was greater in heifers fed M than in control heifers, as the duration (P less than .05) and area under the second GnRH-induced LH curve. In prepuberal heifers, dietary monensin appears to increase hypophyseal capability of releasing LH after a first and second GnRH challenge.

Animals↗
PubMed1979

Prolactin levels in ovariectomized Brahman, Brahman x Hereford and Hereford cows following a 20 mg dose of estradiol-17beta.

Six Brahman (B), six Brahman x Hereford (BxH) and six Hereford (H) chronically ovariectomized cows were injected intramuscularly with 20 mg of estradiol-17beta (E2). The cows were bled via coccygeal vessel puncture immediately before E2 injection, every 2 hr from 0 to 8 hr post-injection, every hr from 9 to 24 hr post-injection and every 2 hr from 26 to 36 hr post-injection. Serum prolactin (PRL) concentrations were quantitated by a validated radioimmunoassay. All cows exhibited a PRL surge following the E2 injection. A PRL surge was defined as a sustained elevation in PRL of at least one standard deviation above the level of PRL before the rise. Nadir levels of PRL prior to the surge did not differ significantly between breeds. Time (hr) to the onset of the E2-induced PRL surge was 5.0, 5.0 and 6.2 in B, BxH and H, respectively (P<.10). Elapsed time (hr) from E2 injection to the PRL peak level varied (P<.01) between B (10.8) and H (17.8) and BxH (11.8) and H. Peak PRL levels (ng/ml) varied (P<.10) between breeds (B, 70.6; BxH, 123.9; H, 49.4). Area under the PRL curve (sq cm) varied (P<.05) between BxH (45.2) and H (24.7) but not between BxH and B (34.3; P>.10) or B and H (P>.10). Duration (hr) of the PRL surge did not differ significantly between breeds (B, 19.3; BxH, 20.5; H, 21.2). Overall, bleeding period effects (P<.01), breed effects (P<.10), and breed x period interactions (P<.01) were found.

Journal Article↗
PubMed1979

Successful superovulation, nonsurgical collection and transfer of embryos from Brahman cows.

Nonsurgical recoveries and transfers of embryos were performed at the McKellar Embryo Transplant Center from 122 superovulated Brahman cows. FSH-P (Armour) was used to superovulate all cows at dose levels ranging from 36 to 48 mg total FSH-P. Luteal regression was induced by use of 40 mg PGF(2(alpha)) in all 122 cows. Embryos were transferred into recipients 6, 7 or 8 days after observed estrus. Embryos were successfully collected from 82% of the FSH-P treated cows. The dose level of FSH-P affected numbers of embryos collected (P<.05). Numbers of embryos collected from cows superovulated with 36-38, 40, 42, 43, 44, 45, 46 and 47-48 mg FSH-P were 2.8 +/- 1.0, 6.8 +/- 1.1, 9.4 +/- 1.4, 10.0 +/- 2.7, 7.1 +/- 1.6, 6.8 +/- 2.0, 5.0 +/- 1.7 and 4.6 +/- 2.0 embryos, respectively. The dose level of FSH-P also affected numbers of embryos transferred (P<.10). Number of embryos transferred from cows superovulated with 36-38, 40, 42, 43, 44, 45, 46 and 47-48 mg FSH-P were 2.8 +/- 1.9, 5.2 +/- 0.9, 6.9 +/- 1.2, 6.7 +/- 2.1, 4.8 +/- 1.3, 5.1 +/- 1.4, 3.4 +/- 1.2 and 3.2 +/- 2.1 embryos, respectively. The developmental stage (D) of the embryo was also a factor in pregnancy rate of recipients (morula = 13.8%, blastocyst = 22.1% and expanded blastocyst = 29.9%; P<.005). The skill of the technician (T) transferring the embryo had a dramatic effect upon subsequent pregnancy rate of the recipients (T 1 = 46.0% vs T 2 = 22.6% pregnancy rate; P<.005). Pregnancy rate of recipients was also affected by the stage postestrus (S) at which the embryo was transferred (day 6 = 23.5%, day 7 = 25.5% and day 8 = 42.3% pregnancy rate; P<.05). Interactions were found between T x S, T x D, S x D and T x S x D (P<.05). These data indicate that use of 40, 42, or 43 mg total doses of FSH-P were quite effective in superovulating the Brahman cow. Recipients transferred on day 8 postestrus achieved higher pregnancy rates than recipients transferred on days 6 or 7 postestrus. Embryos transferred in the expanded blastocyst stage of development proved to yield the highest pregnancy rates in recipients.

Journal Article↗
PubMed1979

Steroid levels after intramuscular injection of radioactive estradiol-17beta, estrone, progesterone and testosterone in the bovine.

Eight 2 year old Hereford cows from days 8 to 12 of the estrous cycle were injected intramuscularly with 5 ml of corn oil containing 5 mg of estradiol-17beta (two cows), estrone (two cows), progesterone (two cows) or testosterone (two cows). Each cow treated with estradiol received 494 microc of estradiol-17beta-6, 7 H3 and each cow treated with estrone received 492 microc of estrone-6, 7 H3. Each cow treated with progesterone or testosterone received 400 muc of H3 compound labeled in the 7 position. Total urine was collected by urethral catheterization of the cows treated with estrogens. Blood samples for plasma and serum were collected via jugular cannulae. Blood and urine samples from estrogen-treated cows were collected hourly for the first 24 hr, at 2 hr intervals for the next 26 hr, at 4 hr intervals for the next 12 hr and at 12 hr intervals until background was reached. Blood samples were collected hourly from 1 to 8 hr after injection from progesterone or testosterone-treated cows. Plasma and serum levels of radioactive estradiol-17beta, estrone, progesterone and testosterone were similar. Blood levels of radioactivity peaked at 2 hr post-injection in cows receiving estradiol-17beta and at 3 hr in cows receiving estrone. Blood levels of labeled estradiol-17beta and estrone were nondetectable by 54 hr and 83 hr, respectively. Peak urinary excretion of radioactivity was reached at 7 hr for estradiol-17beta and at 14 hr for estrone and nondetectable levels were reached by 95 hr for estradiol-17beta and 14 hr for estrone. At these times, 15.5% of the total dose of radioactive estradiol-17beta and 17.5% of the injected estrone had been excreted in the urine. Peak blood and urinary excretion levels were reached earlier for radioactive estradiol-17beta than for estrone, and excretion of estradiol-17beta was completed more rapidly. No difference was found in plasma and serum levels for any steroid studies; thus, endogenous steroid titers in blood plasma and serum are not different in the cow.

Journal Article↗
PubMed1979

Effect of mating stimuli on LH release in bulls.

Fourteen crossbred beef bulls were assigned at random to receive one of four sexual stimuli treatments. Treatments consisted of: (1) controls (four bulls), no visual or physical contact with any cows; (2) false mount (two bulls), allowed to mount an estrual cow; (3) mated (four bulls), allowed to mount an estrual cow with intromission and ejaculation; (4) electroejaculated (four bulls), no exposure to cows. Serum from blood samples taken at 15-min intervals from -15 min to 2 hr from sexual stimuli were radioimmunoassayed for luteinizing hormone (LH). Four bulls had elevated levels at the pretreatment bleeding, but none of the stimuli induced or were associated with LH releases. Basal levels of LH were consistent within bulls but varied considerably among bulls. Conclusion is that stimuli associated with mating do not cause a release of LH.

Journal Article↗
PubMed1979

Temporal relationships among peripheral blood concentrations of corticosteroids, luteinizing hormone and testosterone in bulls.

Interrelationships among peripheral blood concentrations of corticosteroids (CS), luteinizing hormone (LH) and testosterone (T) were evaluated over a 24-hr period in four Angus bulls (18 months of age and 450 kg in body weight). Concentrations of LH and T were determined by radioimmunoassay and concentrations of CS by competitive protein binding assay of blood samples collected via jugular cannula at hourly intervals for 24 consecutive hr. A positive temporal relationship was observed between LH and T as significant positive correlations were obtained between concentrations of LH at one hour and concentrations of T at the subsequent hour in 3 of 4 bulls. Although LH peaks preceded T peaks by 1 hr, variation in this temporal relationship was observed as LH peaks occurred which were not accompanied by T peaks in some bulls. LH peaks were usually preceded by basal or declining concentrations of CS and prolonged elevations in concentrations of CS were often coincident with basal concentrations of LH and T. Negative correlations were obtained between concentrations of CS at one hour and concentrations of LH and T at the subsequent hour. These data describe the positive regulatory role of LH in testicular T production in the bull and suggest that alterations in endogenous concentrations of CS may influence peripheral concentrations of LH and T in the bull.

Journal Article↗
PubMed1977

Urinary creatinine as an index of urinary excretion of estrogen in cows prepartum and postpartum.

Urine was collected from 55 cows via indwelling urinary catheters for periods of 12 h on different days (28 days prepartum to 60 days postpartum). Excretion of urinary creatinine (mg/h per kg bodyweight) among Holsteins increased from .94 on day 28 prepartum to 1.14 on day .5 postpartum and then decreased to .82 on days 30 to 45 of lactation. Excretion of creatinine among 12-h collections of urine on different days did not differ for groups of cows within periods prepartum and postpartum, and coefficients of variation within cows were 12 to 13%. Ratio of urinary estradiol (-17 alpha) to urinary creatinine was correlated (.93) more highly with its excretion based on volume of urine excreted than was its urinary concentration (.79) within periods prepartum and postpartum. Ratios of urinary metabolites to urinary creatinine rather than their concentrations should be used to express rates of excretion in cows' urine when urine excreted per hour is unknown. Moreover, daily rates of excretion of estradiol in urine can be estimated [ng estradiol/day = A X ng/mg urinary creatinine x kg bodyweight x 24 h, where A is average excretion of urinary creatinine (mg/h per kg bodyweight)] for respective days prepartum and postpartum.

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