Biomedical subjects

D N Marple

Publications and source records attributed to D N Marple.

At least 19 recordsLinked to original sources

PubMed1992

Differences in GH secretion from individual somatotropes in rats genetically selected for fast and slow growth.

A reverse hemolytic plaque assay was used to examine effects of selection for fast (F) and slow (S) growth on growth hormone (GH) secretion by individual somatotropes. Anterior pituitaries (AP) from 32 male Charles River CD strain rats selected for F and S growth for 20 generations were used. Four rats per line were used at 4, 6, 8, or 10 wk of age. Body weight (P < 0.0001) of F rats was greater compared with S rats. AP (P < 0.05) were heavier at 8 and 10 wk of age in F compared with S line rats. Percentages of GH-secreting cells were unaffected by age (range = 32.7-35.5%) and line [F = 33.1 +/- 1.2% (SE) vs. S = 34.5 +/- 1.2%] or by human GH-releasing factor (hGRF). At 8 and 10 wk, mean plaque-forming area was greater (P < 0.0001) in F compared with S rats under both nonstimulated (2,704 +/- 202 vs. 1,648 +/- 202 microns2) and hGRF-stimulated secretion (4,503 +/- 202 vs. 2,682 +/- 202 microns2). Results indicate that differences in growth observed in the two lines may be due to a greater secretory capacity of individual somatotropes rather than to a greater percentage of somatotropes or sensitivity of somatotropes to secretagogue.

Aging↗

PubMed1992

Effect of consuming fungus-infected and fungus-free tall fescue and ergotamine tartrate on selected physiological variables of cattle in environmentally controlled conditions.

Two experiments were conducted to determine the physiological responses of consuming a fungus-free (FF) or fungus-infected (INF) tall fescue diet (Exp. 1) or the FF diet plus ergotamine tartrate at 30 ppm (FF/ET, Exp. 2) in a thermoneutral (21 degrees C) or heat-stressed environment (32 degrees C, dry bulb; 10 degrees C dew point). Treatment periods lasted 28 d after a 10-d adaptation period. Experiment 1 was replicated three times, and Exp. 2 was replicated twice, with eight Holstein steers in each replicate (mean BW = 185 kg). Feed intake (FI), rectal temperature (RT), and respiration rate (RR) were recorded daily, and heart rate (HR) and infrared temperatures at the ear canal (ECT), ear tip (ETT), pastern (PT), coronary band (CBT), and tail tip (TTT) were recorded weekly. Consumption of INF and FF/ET compared with FF diets decreased (P less than .10) FI, HR, ECT, PT, CBT, and TTT and elevated (P less than .10) RT and RR by 2.8, 2.77 kg/d; 17, 23 beats/min; .8, 1.1 degrees C; .9, 1.1 degrees C; .8, .9 degrees C; 1.1, 2.6 degrees C; .3, .5 degrees C; and 8, 8 breaths/min; respectively. Ear-tip temperature was reduced (P less than .10) 1.6 degrees C by consumption of INF but not by consumption of FF/ET. Reduction of peripheral temperatures is indicative of reduced blood flow to peripheral areas as a result of vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1991

Endocrine changes in sows exposed to elevated ambient temperature during lactation.

Seven sows were placed into one of two environmental chambers at 22 C, 5 d prior to farrowing. On day 9 of lactation, one chamber was changed to 30 C (n = 4) and the other remained at 22 C (n = 3). On days 24 and 25, blood samples were collected every 15 min for 9 hr and 7 hr, respectively. On day 24, thyrotropin releasing hormone (TRH) and gonadotropin releasing hormone (GnRH) were injected iv at hour 8. On day 25 naloxone (NAL) was administered iv at hour 4 followed 2 hr later by iv injection of TRH and GnRH. Milk yield and litter weights were similar but backfat thickness (BF) was greater in 22 C sows (P less than .05) compared to 30 C sows. Luteinizing hormone (LH) pulse frequency was greater (P less than .003) and LH pulse amplitude was less (P less than .03) in 22 C sows. LH concentrations after GnRH were similar on day 24 but on day 25, LH concentrations after GnRH were greater (P less than .05) for 30 C sows. Prolactin (PRL) concentrations were similar on days 24 and 25 for both groups. However, PRL response to TRH was greater (P less than .05) on both days 24 and 25 in 30 C sows. Growth hormone (GH) concentrations, and the GH response to TRH, were greater (P less than .0001) in 30 C sows. Cortisol concentrations, and the response to NAL, were less (P less than .03) in 30 C sows. NAL failed to alter LH secretion but decreased (P less than .05) PRL secretion in both groups of sows. However, GH response to NAL was greater (P less than .05) in 30 C sows. Therefore, sows exposed to elevated ambient temperature during lactation exhibited altered endocrine function.

Animals↗

PubMed1991

The effects of various dietary phosphorus levels on the circadian patterns of plasma 1,25-dihydroxycholecalciferol, total calcium, ionized calcium, and phosphorus in laying hens.

Six hundred and sixty 75-wk-old Hy-line W36 hens were allocated to one of three dietary levels of total phosphorus, .30, .60, or .90%. Birds were fed the diets for 3 days following which blood samples were collected at six different times, 2, 6, 10, 14, 18, and 22 h postoviposition (POP), and analyzed for 1,25-dihydroxycholecalciferol [1,25-(OH)2 D3], total calcium (TCa), ionized calcium (Ca++), percentage Ca++ to TCa (%Ca++/TCa), and phosphorus (P). Plasma TCa and P significantly (P less than .001 and .025, respectively) peaked at 10 to 14 h POP. The Ca++ and %Ca++/TCa significantly (P less than .001) decreased during eggshell formation and following completion of the shell (22 h POP) levels returned to resting concentrations. Plasma 1,25-(OH)2D3 results confirmed the existence and time of a circadian rhythm in laying hens. Peak concentrations of the metabolite occurred at 10 to 14 h POP, which resulted in a quadratic relationship (P less than .001). Plasma P decreased with decreasing dietary P and plasma 1,25-(OH)2D3 increased (P less than .025). Feeding low dietary P significantly (P less than .001) increased Ca++ and %Ca++/TCa. Results of feeding various levels of dietary P to laying hens indicate that low P stimulates an increase in plasma 1,25-(OH)2D3 as well as Ca++ and %Ca++/TCa, but high P actually suppressed this response.

Animals↗

PubMed1991

Developmental changes in the regulation of plasma growth hormone concentrations in Holstein calves.

A study was initiated to determine whether development of a functional ruminant digestive system was associated with alterations in plasma growth hormone (GH) concentration. Holstein bull calves were fed milk or milk with grain until studied at the age of 1 month (n = 12). Calves placed on pasture with some grain supplementation were studied at the age of 3 months (n = 6) to determine plasma GH concentration in an animal with fully developed ruminant metabolism. Blood samples were taken at 10-minute intervals for 5 hours, followed by administration of bovine GH-releasing factor (0.075 micrograms/kg of body weight) and subsequent blood sample collection for 1 hour. On the following day, a blood sample was collected via jugular cannula, clonidine (10 micrograms/kg) was administered, and blood samples were subsequently obtained. Data indicated that milk-fed calves had higher mean plasma GH concentration than did either milk/grain-fed or older calves. The difference in mean plasma GH concentration was related to higher secretory pulse amplitude. Pituitary responses to bovine GH-releasing factor did not differ among the 3 groups, but response to clonidine were greater in milk-fed calves than in calves of the other groups. These data indicate that the change from a nonruminant to a ruminant-type gastrointestinal tract, perhaps attributable to subsequent changes in metabolism, may induce changes in hypothalmic function to decrease GH concentration.

Aging↗

PubMed1990

Physiological responses to resistance-exercise in athletes self-administering anabolic steroids.

Endocrine and metabolic responses to resistance exercise were compared in 5 athletes self-administering (SL) anabolic steroids and 8 athletes (L) not using these compounds. Exercise consisted of 5 sets of 10 repetitions in the squat and quarter squat. Blood samples were collected before (pre) and immediately after (post) exercise, and following 30 minutes of recovery (post-30). Except for significantly lower lactate concentrations in SL (p less than 0.015) at post-30, the responses to exercise and recovery were similar in both groups. Significantly higher hematocrits (p less than 0.0001), total androgen concentrations (p less than 0.0001), and androgen/cortisol ratios (p less than 0.0001) were observed in the SL group across all time periods. Plasma androgen concentrations increased about 22% in SL following exercise, even though plasma LH concentrations were significantly lower (p less than 0.0001) than in L. Plasma ACTH and cortisol concentrations were not significantly affected. Both groups displayed similar endocrine and metabolic responses to an acute bout of resistance exercise. The higher androgen/cortisol ratios and lower plasma lactate concentrations during recovery are two potential factors which may help explain the lower subjective level of fatigue following training sessions often reported by individuals who use anabolic steroids.

Adrenocorticotropic Hormone↗

PubMed1989

Differential growth hormone responses to glucose and growth hormone releasing hormone in lactating dairy cows.

Dairy cows in early lactation were reported to secrete growth hormone in response to declining glucose concentrations at day 5 but not day 30 post-partum, whereas GH responses to TRH were reported to be enhanced after day 30 post partum. The present study examined GH response following glucose infusion and the effect of GHRH as well as effects of SRIH on GHRH-stimulated GH release. Declining plasma glucose concentrations after glucose infusion stimulated GH release at day 5 post partum but not in nonpregnant, nonlactating cows or in cows at days 30 and 90 post partum. GHRH stimulated GH release on all days tested, but the response was highest at day 30 post partum when compared to other days. Somatostatin infusion inhibited GHRH effects on GH concentrations only at day 30 post partum and in nonpregnant, nonlactating cows. Thus, a differential response of the GH regulatory system could be demonstrated between days 5 and 30 post partum utilizing different stimuli. Evaluation of plasma glucose and free fatty acid concentrations on days 5, 10, 20, and 30 post partum revealed a progressive decrease in FFA but not glucose as lactation progressed. Decreased plasma FFA concentrations were paralleled by a decrease in basal GH, somatomedin-C and epinephrine. Thus, a decline in FFA may be responsible for the disparity between effects of GHRH and glucose on GH release between days 5 and 30 post partum.

Animals↗

PubMed1989

Effects of acute insulin deficiency on catecholamine and indoleamine content and catecholamine turnover in microdissected hypothalamic nuclei in streptozotocin-diabetic rats.

The effects of streptozotocin-induced diabetes on catecholamine and indoleamine concentrations and catecholamine turnover rates in individual microdissected hypothalamic nuclei known, or believed, to be involved in the control of neuroendocrine function, were examined in control, insulin-treated diabetic and acutely insulin-withdrawn diabetic female rats. Streptozotocin-induced diabetes and acute insulin deficiency were demonstrated to result in increased concentrations of epinephrine in the suprachiasmatic nucleus, decreased turnover of epinephrine in the arcuate nucleus and decreased turnover of dopamine in the ventromedial nucleus was found to be increased in the insulin-treated diabetic animals. These data indicate that experimental diabetes and acute insulin deficiency result in the rapid onset of detectable alterations in epinephrine and dopamine activity in specific hypothalamic nuclei. These diabetes-induced changes may cause, or contribute to, the development of secondary neuroendocrine abnormalities known to occur in the diabetic condition.

Amines↗

PubMed1989

Skeletal muscle protein synthesis and growth hormone secretion in young lambs treated with clenbuterol.

To determine effects of clenbuterol (CB) on muscle protein turnover and growth hormone (GH) secretion, 16 crossbred wether lambs (14.4 kg) were randomized into two groups designated to receive daily oral boluses of gelatin capsules containing corn starch with either 0 (control, CTL) or 1.87 mg/kg body weight CB for either 14 (n = 8) or 28 d (n = 8). This calculates to be approximately 40 mg CB/kg diet. Lambs had ad libitum access to a 16% crude protein corn-soy diet and feed consumption (FC) was measured. After 14 and 28 d, lambs were slaughtered and semitendinosus (ST), longissimus (LD) and brachialis (BR) muscles were exercised, weighed and analyzed for protein (TP) content. For 6 h prior to slaughter of 28-d lambs, 2.5 microCi L-[U-14C]tyrosine/kg was infused intravenously, blood was sampled and plasma was analyzed for specific radioactivity of tyrosine. Plasma GH concentrations were assessed by radioimmunoassay. No differences due to treatment were found in FC, rate of gain or GH concentrations. Semitendinosus and BR weights of control lambs at 14 d did not differ between treatments. At 28 d, ST and BR weights of control lambs (58.8 and 18.5 g, respectively) were less (P less than .10) than those of lambs treated with CB (74.3 and 23.1 g, respectively). The TP per ST and BR at 28 d for control lambs was 71.5 and 85.1% (P less than .10) that of muscles of lambs treated with CB. Fractional protein synthesis rates (FSR) of the BR (9.4 vs 6.1%/d) and total protein synthesized in ST muscle per day (1.4 vs .8 g) were elevated (P less than .10) in lambs treated with CB compared to controls. These data suggest that the increased fractional accretion rate observed in lambs treated with CB for 28 d was caused by increased FSR.

Animal Feed↗

PubMed1989

Effects of ad libitum and restricted feeding on semen quantity and quality, body composition, and blood chemistry of caged broiler breeder males.

One hundred eighty, 16-wk-old, caged broiler breeder males were randomly assigned to one of three feeding treatments: 1) restricted feeding (RES), breeder-recommended levels minus 25%; 2) control feeding (CON), breeder-recommended levels; 3) full-fed (FF), ad libitum feeding. Each group received the same corn-soybean diet, with 15.5% CP and 2,878 kcal ME/kg feed. The males were ejaculated twice weekly, and BW, semen characteristics, hematocrits (HCT), and serum testosterone (T) were determined every 4 wk. At 17, 35, and 56 wk of age males were killed for body composition determination of percentages of protein, moisture, and fat. The FF males were heavier throughout the experiment than either CON or RES males. The FF group had a higher percentage of males in semen production than CON, which had a higher percentage of males in production than RES. Males of the FF group produced more semen with a higher spermatozoa concentration (SC) than CON, which males had higher spermatozoan concentrations than RES. The FF males had a higher level of T overall than CON or RES males. Hematocrits of FF were higher than those of CON birds, which were higher than those of RES birds. Body compositions were not significantly different among treatments at 17 wk; however, at 35 and 56 wk, FF males had a higher percentage of fat and a lower percentage of protein than birds in the other two groups. Significant positive correlations were found between body fat and the variables HCT, BW, semen weight (SW), and SC. Body weight was positively correlated with SW, and T was correlated with HCT.

Animal Feed↗

PubMed1989

Effects of dietary energy on semen production, fertility, plasma testosterone, and carcass composition of broiler-breeder males in cages.

One hundred-fifty broiler breeder males were raised to 17 wk of age in floor pens using standard procedures. The males were placed in individual cages at 18 wk of age in an environmentally controlled house and fed for recommended BW to 29 wk of age. At 30 wk of age, birds were randomly assigned to one of five dietary treatments. Diets consisted of 10% CP and 1,600, 2,000, 2,400, 2,800, or 3,200 kcal ME/kg feed (Groups 1600, 2000, 2400, 2800, and 3200, respectively). Birds were ejaculated twice weekly; semen characteristics, BW, and serum testosterone (T) were determined every 4 wk. Fertility determinations were made at 38 and 48 wk. At the end of the experiment (60 wk of age), body composition was measured. The percentage of body fat was reduced in Groups 1600, 2000, and 2400. Body weight, percentage of males producing semen, semen weight (SW), total spermatozoa per ejaculate (TS), and T were all reduced in Groups 1600 and 2000; semen concentration (SC) was reduced in Group 1600, compared to the other treatments. Group 2400 had the highest percentage of carcass protein; Groups 1600 and 3200, the lowest percentage. Body weight, percentage of protein, and percentage of fat were quadratically related to dietary energy. The T, SW, SC, and TS were linearly and positively related to the energy level.

Animals↗

PubMed1988

Adenohypophyseal receptors for LHRH, pituitary content of gonadotropins and plasma concentrations of LH in cyclic, pregnant and postpartum beef cows.

Adenohypophyseal concentrations of LHRH receptors, pituitary content of LH and FSH, and plasma concentrations of LH were determined in thirty Hereford, Angus or Hereford-Angus heifers that were randomly assigned by breed and weight to five periods including day 3 of the estrous cycle (CY), pregnant day 120 (P120), 200 (P200), 275 (P275), or day 2 postpartum (PP). Jugular blood samples were collected at 10-min intervals for 8 hr from all cows. Within 2 hr after completion of blood sampling, animals were slaughtered and the pituitary gland frozen at -196 C. LH pulse frequency/8 hr was reduced (P less than .05) during gestation (.5, .2, and 1.5 +/- .5/8 hr, for P120, P200, and P275, respectively) and PP (.5 +/- .5/8 hr) compared to CY (7.8 +/- .5/8 hr). Frequency of LH pulses/8 hr was not different (P greater than .1) among P120, P200 or PP periods but was different (P less than .05) between P200 and P275. There were no differences in LH pulse height (P greater than .1) among periods; however, pulse amplitude was greatest (P less than .05) at P120 (1.3 +/- .2 ng/ml) and lowest between P200 and PP (.6 to .8 +/- .2 ng/ml). Baseline concentrations of plasma LH did not differ (P greater than .1) among P and PP periods (.3 +/- .1 ng/ml), but were lower (P less than .05) than in CY animals (.7 +/- .1 ng/ml). Concentration of adenohypophyseal LHRH receptors was approximately two-fold greater (P less than .05) at P120 (25.85 +/- 2.2 fmol/mg) than at all other periods (9.5 to 14.9 +/- 2.2 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Secretory patterns and metabolic clearance rate of porcine growth hormone in swine selected for growth.

Eleven Landrace pigs (six boars and five gilts, 50 kg) representing lines selected for three generations for maximum weight at 200 d of age were compared to eight pigs (four boars and four gilts, 50 kg) representing contemporary randomly selected Landrace controls to determine the effect of selection for growth on the metabolic clearance rate (MCR) and plasma concentrations of porcine growth hormone (GH). To estimate MCR of GH, the disappearance of a bolus of porcine GH was monitored over 120 min following its i.v. injection. Blood samples also were collected every 15 min over a 6-h period before injecting GH to determine baseline and overall mean GH concentrations, mean peak amplitude and number of GH secretory episodes. Boars exhibited greater overall mean GH concentrations (4.80 vs 3.11 ng/ml; P less than .05) and had greater maximum GH concentrations associated with secretory episodes (16.11 vs 10.80 ng/ml; P less than .05) than did gilts. There were no differences between boars and pigs exhibited greater baseline GH concentrations (2.04 vs 1.25 ng/ml; P less than .01) than did those from the unselected Landrace line. Selected and control pigs exhibited similar (P greater than .15) overall mean concentrations of GH, frequency of secretory episodes, amplitude of GH peaks and MCR. These data demonstrate that pigs selected for heavier weight at 200 d of age had greater basal plasma GH concentrations than did unselected control pigs.

Animals↗

PubMed1988

Proliferation of skeletal muscle satellite cells after castration and administration of testosterone propionate.

Thirty-six neonatal pigs were randomly assigned to the following treatment groups: sham implanted gonadally intact males (B), sham-implanted castrated males (C), or castrated males implanted with testosterone propionate (C + TP). Four pigs from each group were sacrificed at 7, 14, or 21 days of age after a 6-hr continuous infusion of [3H]thymidine. Myofibers isolated from the triceps brachii were prepared for satellite cell enumeration by light microscope autoradiography. A developmental decline in labeled myofiber nuclei occurred in all groups, however, the greatest decline occurred in C (P less than 0.01). A treatment-by-age interaction was observed for percentage of labeled nuclei. Castration reduced total and labeled nuclei per millimeter myofiber (P less than 0.05), and C + TP had a higher percentage of labeled nuclei than C (2.8 vs 2.2%; P less than 0.05). Since triceps brachii muscles from 21 day B and C + TP were 120% (P less than 0.05) of C, the results indicate that postnatal growth of skeletal muscle is dependent on satellite cell mitotic activity and that testosterone enhances this activity in neonatal pigs.

Animals↗

PubMed1987

Effects of parachlorophenylalanine, quipazine and cyproheptadine on growth hormone and adrenocorticotropin secretion in steers.

Adrenergic and perhaps dopaminergic neurons provide inhibitory regulation of growth hormone (GH) secretion in ruminants. This suggests that either serotonergic or other neurons regulate the stimulatory release of GH. The nature of neurotransmitter control of adrenocorticotropin (ACTH) secretion in ruminants has not been determined. Parachlorophenylalanine (PCPA; serotonin synthesis inhibitor), quipazine (serotonin receptor agonist) and cyproheptadine (serotonin receptor antagonist) were utilized in Holstein steers to determine whether serotonin receptors mediate stimulatory actions on GH and ACTH secretion. PCPA (100 mg/kg BW) administered each day at 1900 hr for three successive days did not alter mean GH concentrations, amplitude of GH peaks, nor the number of GH peaks. Likewise, PCPA altered none of these parameters for ACTH. Quipazine injected iv at .1 or .5 mg/kg BW increased plasma GH (P less than .05) and ACTH (P less than .001) concentrations. There was a dose effect of quipazine on both GH (P less than .05) and ACTH (P less than .0001) secretion. Pretreatment of steers with cyproheptadine (.06 and .6 mg/kg BW) reduced the stimulation of GH by quipazine (P less than .0001) and decreased basal GH concentrations (P less than .0004). Cyproheptadine at .06 mg/kg BW did not alter quipazine effects on ACTH, however, the higher dose decreased the peak ACTH response (P less than .02) to quipazine. Studies with quipazine and cyproheptadine indicated that serotonergic mechanisms are likely involved in the regulation of GH and ACTH secretion in steers.

Adrenocorticotropic Hormone↗

PubMed1987

Effect of photoperiod and temperature on prolactin secretion in ovariectomized gilts.

Five ovariectomized (OVX) gilts were placed in each of two chambers at 20 C with a photoperiod of 12 h light and 12 h dark for 8 d (12L:12D). On d 1, blood samples were collected via jugular cannula every 30 min from 0830 to 1630. At 1630, 200 micrograms of thyrotropin releasing hormone (TRH) were injected iv and blood samples taken every 10 min for 1 h and every 30 min for the next 2 h. On d 2, samples were taken every 30 min from 0830 to 0930 and from 1530 to 1630. Temperature was changed to 10 C or 30 C on d 3. Samples were taken from 0830 to 1630 on d 3, 4 and 9. At 1630 on d 9, the TRH challenge was repeated. Mean basal serum concentrations of prolactin (PRL) were similar for all gilts and for all periods. However, serum PRL response (ng PRL X ml-1 X 150 min-1) to TRH increased (P less than .0001) after exposure to 30 C, while exposure to 10 C failed to alter PRL response. In Exp. 2, six ovariectomized gilts were assigned to each chamber. The protocol of Exp. 1 was followed through d 3, except temperature and photoperiod were changed to 10 C and 8L:16D or 30 C and 16L:8D. On d 34 the TRH challenge was repeated. Mean basal serum concentration of PRL was similar for all gilts and all periods. However, simultaneous increases in temperature and photoperiod increased (P less than .005) serum PRL response to TRH, whereas simultaneous decreases in temperature and photoperiod failed to alter PRL response to TRH.

Animals↗

PubMed1987

Effect of animal density on endocrine development in gilts.

A study was conducted to determine the effect of social crowding on the development of endocrine organs involved in the reproductive process in growing and finishing gilts. One hundred four littermate gilts weighing approximately 30 kg were randomly assigned to treatment groups of either 8 or 16 pigs/pen. Gilts raised in pens of eight were allotted 1.06 m2 per pig from 30 to 65 kg and 1.25 m2 from 65 to 100 kg; whereas, one-half the area was provided for gilts raised in pens of 16. Littermate gilts raised in pens of 8 and 16 were slaughtered on the same day when the average weight of pigs reached 100 kg. At slaughter, the brain, adrenals, pituitary, uterus and ovaries were removed and weighted. The brain was lyophilyzed and reweighed to yield dry brain weight. Gilts raised in the low-density groups had heavier adrenal (P less than .01), pituitary (P less than .08), brain (P less than .11), dry-brain (P less than .02), uterine (P less than .09) and ovarian (P less than .07) tissues. Furthermore, significantly more gilts in the low-density, compared with the high-density groups, had ovulated at slaughter. In a second study, eight littermate gilts raised in pens of 8 or 16 and weighing approximately 100 kg were moved to individual pens and fitted with a jugular vein catheter. Following blood sample collection at 15-min intervals for 2 h, 200 IU of adrenocorticotropin (ACTH) were infused into the cannula. Blood samples were collected at 15-min intervals for an additional 2 h. There were no differences between basal or ACTH-stimulated concentrations of plasma cortisol between treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1986

Body composition and other physical parameters as determinants of age at sexual maturity and performance efficiency in dwarf hens divergently selected for body weight.

Hens in this study were produced from random breeding within lines (high, low, and control) of dwarf White Leghorns that had been divergently selected for four generations for 20-week body weight. Birds were weighed at 10 weeks of age and placed in individual cages at 18 weeks of age. Body weights, shank lengths, and egg weights were obtained at sexual maturity (day of first egg) and at 4, 8, 12, and 16 weeks after sexual maturity. Egg production was recorded during 28-day periods. Thirty hens/line were sampled at sexual maturity and at the above times after sexual maturity for body composition (percent fat, protein, moisture, and ash). High line hens showed increased percent body fat and reduced percent protein and moisture compared to low and control hens. Coefficients of determination (R2) for age at sexual maturity and body weight were small (R2 less than or equal to .20) for high and control hens. There were no meaningful relationships between body weight or other physical measurements and sexual maturity in low hens. There were no significant relationships between body composition and age at sexual maturity in high and control hens. There was a strong cubic association (R2 = .73; P less than .001) between percent ash and age at sexual maturity in low hens, although the biological importance of this relationship was uncertain. Coefficients of determination between body weight and performance efficiency (egg mass per body weight) were small to moderate (R2 = .04 to .46) for high and control hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗