Search PubMed⌕ Search

Biomedical subjects

D L Davis

Publications and source records attributed to D L Davis.

At least 163 records · Page 9Linked to original sources
PubMed1987

Endocrine changes before and after weaning in response to boar exposure and altered suckling in sows.

Eighteen sows (6 primiparous and 12 multiparous) were allotted randomly within parity to two lactational treatments: litter separation (LS; 6 h/day) plus boar exposure (BE; 1 h/day; N = 14) beginning 8 days before weaning (4 weeks) and no LS + no BE (controls; N = 4). Blood was collected from all sows via indwelling venous catheters at 20-min intervals for 5 h on Days -1, 0, 1, 2 and 3 from start of treatment. Control sows and those exposed to LS + BE not exhibiting oestrus during lactation were resampled on Days -1, 0, 1 and 2 from weaning. All 10 multiparous sows receiving LS + BE exhibited oestrus during lactation, whereas none of the 4 primiparous sows exposed to LS + BE or the 2 control multiparous and 2 control primiparous sows exhibited lactational oestrus. Overall concentrations of LH in serum were higher (P less than 0.05) in sows receiving LS + BE than in control sows during lactation, whereas overall FSH was higher (P less than 0.05) in primiparous than multiparous sows. Number and amplitude of pulses of LH were greater (P less than 0.05) for treated primiparous than multiparous sows during lactation. Oestradiol-17 beta increased (P less than 0.05) in sows during LS + BE and was higher (P less than 0.01) in multiparous sows of this group than control multiparous or treated primiparous sows. Preweaning concentrations of cortisol and progesterone in serum were higher (P less than 0.05) in treated than control sows for multiparous and primiparous animals. In sows resampled at weaning, the number of pulses of LH was greater (P less than 0.05) in treated primiparous than in control sows. Postweaning concentrations of FSH in serum were unaffected by preweaning treatments. It was concluded that (1) litter separation and boar exposure increased basal and pulsatile secretion of LH in multiparous and primiparous sows; (2) lack of ovarian follicular development and oestradiol secretion may preclude expression of oestrus in primiparous sows during lactation, despite elevated concentrations of FSH and LH in serum; and (3) if elevated concentrations of cortisol and progesterone inhibit the onset of oestrous cycles, in response to litter separation and boar exposure during lactation, the effect is limited to primiparous sows.

Animals↗
PubMed1987

Estrous and litter traits in gilts altered by altrenogest, flushing and pubertal status.

Influences of estrous synchronization with altrenogest and flushing on reproductive traits in gilts were evaluated in three experiments on two farms. Crossbred gilts were fed altrenogest or altrenogest and an additional 1.55 kg ground sorghum grain for at least 10 d before breeding (flushing), or served as controls. Additional grain for the flushing treatment was provided to gilts from the eighth day of altrenogest treatment until they were detected in estrus. The combination of altrenogest and flushing (on Farm A) increased (P less than .05) litter size when compared with gilts treated only with altrenogest and controls that received neither altrenogest nor flushing. This response was entirely among gilts inseminated at their pubertal estrus. For pubertal gilts fed altrenogest and the flushing treatment, litter traits were similar to other treated or control gilts inseminated at a postpubertal estrus. No treatment effects on litter size were detected for gilts inseminated at a postpubertal estrus. Gilts on Farm B responded differently, with larger litter sizes (P = .08) for those treated with altrenogest and flushing plus altrenogest than for control gilts. Reasons for farm differences might be unidentified genetic or management factors or different seasons of the year when gilts were treated on Farm B (summer) vs Farm A (fall, winter and spring). Our results indicate a marked potential for increasing litter size in gilts mated at their pubertal estrus because their unstimulated ovulation rate (no altrenogest or flushing) did not challenge adequately the biological capacity of their uteri.

Animal Nutritional Physiological Phenomena↗
PubMed1987

Influence of duration of litter separation and boar exposure on estrous expression of sows during and after lactation.

The influence of litter separation (LS) that included a change in housing environment and social status of sows, boar exposure (BE), and parity on estrous expression by sows during and after lactation was examined in two experiments utilizing 140 crossbred sows. In Exp. 1 (Yorkshire X Duroc sows), limiting duration of LS to 6 or 3 h/d during the last 8 d of lactation in two trials, while maintaining 1 h BE, resulted in similar proportions of sows in estrus during lactation (65 vs 79% for 3- and 6-h sows). However, 6-h LS tended to reduce (P = .08) the interval to estrus by .6 d for those sows that expressed a preweaning estrus. Postweaning intervals to estrus were unaffected by duration of LS in the remaining sows. In Exp. 2, sows (Yorkshire X Duroc X Chester White) were assigned to four treatment groups during the last 8 d of lactation: 1) BE (1 h/d), 2) LS (6 h/d), 3) LS + BE and 4) no LS + no BE (control). Only nine sows expressed estrus during lactation; four of 28 LS sows and five of 28 LS + BE sows. No sows were in estrus before weaning during August 1985 and only one sow (LS group) was in estrus before weaning during October 1986. Postweaning intervals to estrus were reduced (P less than .05) by .9 d after preweaning BE compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The meaning of menopause in a Newfoundland fishing village.

A comparison of etic and emic options for climacteric research shows that the emic option is best suited to the study of the meaning of menopause in the Southwest coast Newfoundland outport fishing village of Grey Rock Harbour. Standard menopause survey instruments, as the Neugarten Attitudes Toward Menopause checklist (1963) and the Datan et al. Sociocultural Patterns and the Involutional Crisis interview schedule (1981) were administered to 38 women and found to be of limited utility because they assume the following: that respondents can rank stimuli along linearly constructed continuums, that the questionnaire items contain sufficient contextual information for Harbour women to make psychosocial judgements such as agree and disagree, and that respondents are capable of and experience no difficulty in making public pronouncements based on insightful self-evaluations. More qualitative ethnographic description and emic analysis address, yet go beyond, the popular semantics of menopause to explore the meaning of middle-aging in the symbolic, moral and institutional spheres of Harbour life. For more suitable context for understanding the role that sociocultural factors can play in shaping women's experience of middle-aging, in depth analyses of the following are offered: the continued importance of the fishery and the idealized social image of outport Newfoundlanders as a "tough race"; the expectation that women should endure hardship and solve problems rather than create them; and the strict enforcement of an egalitarian ethic throughout the community.

Climacteric↗
PubMed1986

Increasing trends in some cancers in older Americans: fact or artifact?

In analyzing U.S. cancer mortality from 1933 to 1978, Doll and Peto speculated that recently recorded increases in mortality among those over age 64 were likely to be artifacts, reflecting deaths previously misattributed to such causes as nonspecific cancer, pneumonia, and senility and other ill-defined causes. We test this hypothesis by examining some age-specific, cause-specific mortality in persons 35 to 84 for the period of the 8-ICDA, 1968-1978, which corresponds to the last eleven years of the period studied by Doll and Peto. Our analysis reveals increasing trends in mortality from lung cancer, brain cancer and multiple myeloma in older whites and nonwhites along with increases in several potentially miscoded causes of death from 1968 to 1978. Thus, these increasing cancers in the elderly cannot be explained solely as artifacts. Further studies of trends in site-specific cancer mortality should include age groups through at least age 85. Continued monitoring of site-specific cancer mortality patterns, particularly among the elderly, remains crucial for developing preventive strategies to reduce cancers.

Adult↗
PubMed1986

Tibial nerve and deep fibular nerve effects on venous and extravascular volumes.

The innervation of the vasculature of the dog hindpaw separately controls the series and parallel coupled vessels by means of the tibial, deep fibular, and superficial fibular nerves. The latter primarily affects veins. The venous effects of the tibial and deep fibular nerves have not been adequately defined. The right hindpaw of anesthetized dogs was vascularly and neurally isolated in a volume recorder. The animals were heparinized and the preparation autoperfused (constant pressure). Total tissue volume changes were determined by the volume recorder. Total vascular volume changes were calculated from changes in paw 51Cr-red blood cell radioactivity measured by a scintillation detector. Arterial pressure and paw blood flow were monitored. The tibial and deep fibular nerves were each separately stimulated at 1, 5, and 15 Hz. Deep fibular nerve stimulations resulted in progressively significant increases in precapillary flow resistance. Vascular and tissue volumes decreased with stimulation frequency but vascular volume decreased significantly less than tissue volume change. Tibial nerve stimulation resulted in significant precapillary resistance increases. Vascular and tissue volumes decreased by similar amounts. Thus, deep fibular nerve stimulation causes passive decrease in venous volume, reduced capillary pressure, and fluid absorption. Tibial nerve stimulation causes active arterial and venous constriction maintaining capillary pressure with minimal fluid transfer.

Animals↗
PubMed1986

Dependence of the length-tension relationship on agonist concentration in vascular smooth muscle.

This study examines the dependence of the length-tension (L-T) relationship in vascular smooth muscle on its level of activation. A horizontal shift of the L-T relationship with a change in activation level has been shown in striated muscle when L-T curves could not be superimposed. Active force at each length was normalized to the maximum active force in each curve. Indices of a horizontal shift of a L-T curve include the initial length for an active response (Li) and the length for maximum active force (Lmax). In this study normalized L-T curves were obtained from rings of the dog anterior tibial artery at low (approximately ED50) and high (maximal activation) concentrations of potassium (K+), norepinephrine (NE), and calcium (Ca2+). The normalized curve with a low concentration of K+ or NE was shifted to the right of the curve obtained with a high concentration. Li and Lmax were significantly longer for a low concentration of K+ or NE than a high concentration. With the same concentration of NE (10(-5) M) no difference in the normalized L-T curves, in Li, or in Lmax were found when low (0.085 mM) Ca2+ experiments were compared to normal (1.7 mM) Ca2+ experiments. It may be concluded that the length-tension relationship in vascular smooth muscle is shifted to longer lengths with a decrease in the concentration of a chemical agonist but not by a decrease in external calcium. We suggest that a concentration dependent shift in the length-tension relationship may have a role in the regulation of blood flow.

Animals↗
PubMed1985

Source derivation of the brain-stem auditory evoked potential.

This study described the results of applying source derivation to the brain-stem auditory evoked potential. Unilateral stimulation gives rise to current sinks, associated with waves I and III, which are located in the vicinity of the ipsilateral mastoid. Waves II and V are associated with a pair of current sinks which appear bilaterally in the vicinity of each mastoid.

Adult↗
PubMed1985

Treatment planning for the patient who is incompetent to stand trial.

National attention has focused on criminal defendants who plead not guilty by reason of insanity, but the insanity defense is rarely successful. A far larger number of criminal defendants, estimated at 9,000 annually, are admitted for forensic and civil hospitals because they are found incompetent to stand trial. Once hospitalized, many of these defendants face the likelihood of indefinite commitment. This paper discusses issues related to he concept of incompetency to stand trial and presents an approach to treatment planning and programming designed to restore patients to competency.

Commitment of Persons with Psychiatric Disorders↗
PubMed1985

Assessing the power and quality of epidemiologic studies of asbestos-exposed populations.

This paper briefly discusses criteria for evaluating epidemiologic studies for risk assessment purposes, using asbestos as an example. Asbestos is one of the few carcinogens for which substantial data exist on exposures to humans. However, there are major difficulties in using these data for conducting risk assessments. In particular, exposure data are often incomplete, and risk assessments usually involve extrapolating from the higher exposures of the occupational environments to the lower levels typically encountered in the nonoccupational environment. The term "asbestos" refers to the fibrous form of several minerals, and levels of exposures to these fibers are not easily assessed. Criteria for evaluating epidemiologic studies used in an Ontario Royal Commission report on asbestos are discussed. The importance of considering the statistical power of studies to detect an excess risk is examined using as examples major cohort studies of asbestos-exposed workers, as summarized in a report by the U.S. National Research Council.

Asbestos↗
PubMed1985

Catechol estrogen formation by pig blastocysts during the preimplantation period: biochemical characterization of estrogen-2/4-hydroxylase and correlation with aromatase activity.

Formation of the catechol estrogens 2- and 4-hydroxyestradiol (2-OHE2 and 4-OHE2) from estradiol by pig blastocysts was studied using a direct product isolation assay for estrogen-2/4-hydroxylase (E-2/4-H). Blastocyst E-2/4-H activity was characterized biochemically using homogenates of blastocysts obtained on day 12 of pregnancy. This information was used to establish appropriate incubation conditions for the assay of E-2/4-H activity in blastocysts during the preimplantation period. Catechol estrogen formation was linear with time for up to 30 min and with blastocyst protein concentrations of up to 100 micrograms in a reaction volume of 150 microliters. The E-2/4-H activity of pig blastocysts was maximal at pH 7.9 and was not affected by the nonionic detergent Tween-80. The E-2/4-H activity was dependent on nicotinamide cofactor, with NADPH preferred over NADH for 2-OHE2 formation. The predominant catechol estrogen formed was 2-OHE2: maximum velocities (Vmax) for the formation of 2- and 4-OHE2 were 1570 and 174 pmol/mg protein . 30 min, respectively. The apparent Km values with respect to estradiol for 2- and 4-OHE2 were similar, 4.39 and 4.27 microM, respectively. Blastocyst E-2/4-H activity was detectable in one of two samples of blastocysts from day 10 of pregnancy (4.4 pmol 2-OHE2/mg protein . 30 min), increased to a maximum on days 12 and 13 (628 +/- 153 and 516 +/- 227 pmol 2-OHE2/mg protein . 30 min, respectively), and declined by day 14 (63.2 +/- 32.9 pmol 2-OHE2/mg protein . 30 min). The activity of E-2/4-H was positively correlated with aromatase activity assayed in the same tissue samples from days 10-14 of pregnancy. The surge in E-2/4-H activity coincides with several of the critical events that occur near the time of implantation. Our findings are consistent with the hypothesis that catechol estrogens mediate some of the actions of estrogens in early pregnancy in the pig.

Animals↗
PubMed1985

Scheduled breeding of gilts after estrous synchronization with altrenogest.

Fertility of 104 gilts artificially inseminated (AI) at a predetermined time (scheduled AI) after estrous synchronization with altrenogest (15 mg X gilt-1 X d-1 for 18 d) was compared with that of 103 gilts checked for estrus (estrus checked) and inseminated after altrenogest. Scheduled-AI gilts were inseminated once on d 5, 6 and 7 after the last altrenogest feeding (d 0). Estrus-checked gilts were exposed to a boar twice daily at 0830 and 1630 h and inseminated after the second and third estrous detection period following first detected estrus. Percentage of gilts assigned to treatment that farrowed (72.8 vs 67.3%), total pigs farrowed (11 +/- .4 vs 11.3 +/- .4) and pigs born alive (10.1 +/- .4 vs 10.5 +/- .4) were similar for estrus-checked and scheduled-AI gilts, respectively. We conclude that scheduled AI can be used with estrous synchronization for gilts and may have advantages in breeding herd management and the use of AI in swine.

Animals↗
PubMed1985

Reproductive traits of sows penned individually or in groups until 35 days after breeding.

We compared estrous and farrowing traits in 274 Duroc X Yorkshire sows penned either in individual gestation stalls or in groups (four or five sows/group) during the intervals from weaning to breeding and from breeding to 30 to 35 d after breeding. Sows were assigned to treatment by parity (primiparous vs multiparous), checked twice daily for estrus from 3 to 10 d after weaning and artificially inseminated (AI) twice during estrus. Ovaries of anestrous sows were examined at laparotomy. No major treatment effects on estrous response were detected and 88% (45/51) of anestrous sows had only small ovarian follicles. Litter traits were not affected by penning treatments. However, penning sows in groups postbreeding resulted in a 50% reduction (P less than .05) in early pregnancy losses as indicated by low serum progesterone 19 to 23 d after AI or return to estrus by 23 d after AI. This resulted in a 12 percentage point higher (P less than .05) farrowing rate for group-penned (78%) than for individually penned sows (66%).

Animals↗