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Biomedical subjects

T G Dunn

Publications and source records attributed to T G Dunn.

At least 37 records · Page 2Linked to original sources
PubMed1982

Alterations in follicular steroid hormones during the preovulatory period in the ewe.

Progesterone, testosterone and estradiol-17 beta were quantified within the thecal layer, granulosal layer and fluid of the preovulatory follicle and in ovarian and jugular venous sera of sheep. Prior to the preovulatory surge of luteinizing hormone (LH), the total content of estradiol-17 beta was elevated within each follicular constituent. These levels diminished rapidly to minimal values concurrent with the surge of LH. Follicular tissue and fluid contents of testosterone were low at all times, but were higher before the surge of LH and subsequently (like estradiol-17 beta) declined. The initial decrease in follicular estradiol-17 beta occurred before the first detected decline in testosterone. Changes in sera concentrations of estradiol-17 beta in the ovarian vein draining the ovary with the preovulatory follicle or in the jugular vein were similar to follicular variations in estradiol-17 beta. Likewise, changes in concentrations of testosterone in ovarian venous sera were indicative of follicular changes. Testosterone was undetectable in jugular venous sera. During the period leading up to the anticipated time of ovulation, and approximately 8 h after follicular testosterone and estradiol-17 beta had fallen, content of progesterone within thecal tissue, granulosal tissue and follicular fluid increased. Alterations in follicular progesterone were not reflected by hormone changes in either ovarian or peripheral sera.

Animals↗
PubMed1982

Relationship of growth and puberty in beef heifers fed monensin.

An experiment was designed to determine the effects of dietary monensin on age and weight at puberty in Bos taurus crossbred beef heifers. One hundred and forty heifers were allotted to two weight classes: heavy (H) and light (L) groups, consisting of heifers above and below the average weaning weight, respectively. Heifers within each weight class were assigned to one of three diets during a 203-d winter feeding period: (1) R, 80% roughage: 20% concentrate; (2) M1, R diet plus monensin (200 mg/head daily) with feed intake restricted to produce average daily gains (ADG) similar to R and (3) M2, R diet plus monensin (200 mg/head daily). ADG was higher (P less than .001) for M2 heifers than for R and M1 heifers, which performed similarly. Age and weight at puberty were similar across treatments in L heifers. However, in the H group, HM1 and HM2 heifers were younger (P less than .07) at puberty than HR heifers and this difference was not removed by covariate adjustment of either ADG or body weight. Weigh at puberty was greater (P less than .01) for HM2 heifers than for HM1 or HR heifers; however, this difference was removed by covariate adjustment of either ADG or body weight. Ninety-one percent of LM2 heifers and 100% of all other groups had reached puberty before the breeding season. Pregnancy rates did not differ significantly between treatment groups. Supplementation of a high roughage diet with monensin decreased age at puberty of heifers in the heavy weight class and this decrease was not due to increased body weight or ADG. Perhaps heifers with above average weaning weight possess a greater inherent growth potential than heifers below the average weaning weight and hence are more capable of utilizing monensin to an advantage.

Acetates↗
PubMed1981

Estriol- and estradiol-17 beta-induced luteinizing hormone release in ovariectomized cows and ewes.

Two studies were conducted with ovariectomized animals to compare luteinizing hormone (LH) responses during the 24-hr period following an IM injection of either estriol or estradiol-17 beta. In Exp. 1, six long-term ovariectomized (6 months) beef cows were randomly assigned to be given 1 mg of estriol or estradiol 17 beta injected in 4 ml of corn oil. Two months later, the experiment was replicated in a switch back design. In Exp. 2, eight ewes that had been ovariectomized for 1 to 4 months were randomly assigned to be given 150 micrograms of estriol or estradiol-17 beta injected in 1.5 ml of corn oil. The initial increase in serum LH concentrations occurred earlier in both cows (P less than .01) and ewes (P less than .05) in response to estriol (8 to 9 hr) than in response to estradiol 17 beta (12 to 18 hr). In addition, duration of the decrease in LH release that occurred 1 hr after estrogen injection in ewes was 3 hr shorter (P less than .05) in response to estriol than in response to estradiol-17 beta. The total area under the LH response curve was greater for both cows (P less than .05) and ewes (P less than .01) given estradiol-17 beta than for those given estriol. Administration of estradiol-17 beta induced a 10-fold increase in serum estradiol-17 beta concentrations and a two to fourfold increase in serum estrone concentrations. Both estrogens returned to basal concentrations by 24 hr after administration. Peak serum estriol exceeded 300 pg/ml within 1 hr of estriol injection, but decreased to nondetectable levels within 12 hours. We concluded that estriol can stimulate LH release from the pituitary. Furthermore, the differential LH response to the two estrogens suggests that the positive effects of estriol are mediated earlier but that estradiol-17 beta is a more potent stimulus when administered as a single IM injection.

Animals↗
PubMed1980

Nutrition and the postpartum interval of the ewe, sow and cow.

The effects of nutrition on the length of the postpartum interval (PPI, the interval from parturition to the first postpartum estrus that is accompanied by ovulation) were reviewed for the ewe, sow and cow. Unfortunately, information on the effects of nutrition on the PPI of the mare is nonexistent. Absence of estrus following weaning is a problem in postpartum sows, especially during the summer. High feed intake (more than 3 kg daily) immediately after weaning decreases the incidence of anestrus in sows of some breeds, but not in others. The incidence of prolonged intervals between weaning and estrus and the incidence of anestrus is more frequent in primiparous than in multiparous sows. The effect of nutrition on the PPI of the ewe is more controversial than that for the sow. In mature Merino ewes, neither lactation nor undernutrition during lactation affects the duration of the PPI while both factors increase the length of the PPI in coarse-wool breeds. Undernutrition during lactation increases the incidence of anestrus in primiparous fall-lambing Merino ewes. A cow must conceive by 80 days postpartum to have a 365-day calving interval. Excessive length of the PPI in dairy cows does not appear to be one of the major detriments to fertility since most dairy cows have a PPI of considerably less than 80 days. While feeding high protein diets to high-producing dairy cows shortens the PPI; this practice also increases the interval from parturition to conception. Weight changes, both before and after calving, and body condition at calving interact to affect the PPI of suckled beef cows. The length of the PPI in cows that are in good body condition at calving is not affected by either pre- or postpartum weight changes. More cows in moderate and thin body condition showed estrus by 60 days postpartum if the cows had gained weight prior to calving compared with those that lost weight prior to calving. A high percentage of thin cows that lose weight prior to calving does not show estrus following calving unless they gain weight after calving. The length of the PPI is affected by many factors, for example: parity, breed, lactation, environment and endocrine status. Designs of future experiments must be cognizant of these factors and the possible interactions of these factors with the nutritional status of the animal.

Animal Nutritional Physiological Phenomena↗
PubMed1979

Effect of norgestomet on peripheral levels of progesterone and estradiol-17beta in beef cows.

Peripheral levels of progesterone and estradiol 17beta were quantified in 27 cycling cows following administration of a single Hydron ear implant (G. D. Searle and Co.) containing 2, 4 or 6 mg norgestomet or controls which received no implant. Implants were inserted subcutaneously in the ear on day 15 of the estrous cycle (day of estrus = day 0) and removed 9 days later. The 4 mg (seven of seven cows) and 6 mg (six of six cows) implants suppressed estrus; however, three of eight cows in the 2 mg group exhibited estrus prior to implant removal. The 6 mg implant group had a significantly longer interval from implant removal to estrus than either the 2 or 4 mg group. Failure to detect differences in the rate at which progesterone declined indicated norgestomet treatment did not affect normal corpus luteum regression. Estradiol levels rose at a similar rate approaching estrus in all treatments. There was no indication of increased endogenous estradiol levels due to norgestomet treatment.

Journal Article↗
PubMed1976

Isolation and identification of metabolites of 14C-labeled estradiol in cattle.

A total of six steers and six heifers received three daily injections containing either 200 muCi (1 mg) of [4-14C] estradiol-17beta or 312 muCi (2.16 mg) of [4-14C] estradiol 17beta 3-benzoate. Major metabolites of the administered estradiol-17beta and estradiol-17beta 3-benzoate were identified in muscle, fat, liver, and kidney samples obtained 3 hr after the final injection. Estradiol benzoate was nondetectable in the tissues analyzed, suggesting rapid hydrolysis of the benzoate ester. Consequently, the relative proportions of the various metabolites were similar for both the injected estrogens. Estradiol-17beta and estrone, which together accounted for 80-90% of the total extracted radioactivity, appear to be the major metabolites in both muscle and fats. In contrast, the major metabolites present in liver and kidney appear in the conjugate fraction. Most of the conjugated metabolites were glucuronates, which represent 85-95% of the total recovered conjugate radioactivity.

Adipose Tissue↗