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An experiment was carried out to investigate the effects of age of laying hens (young = 22 wk vs old = 120 wk) in maintaining Ca homeostasis during periods of Ca depletion then repletion with Ca. Plasma Ca and P, tibia breaking strength and percentage ash, renal 25-hydroxycholecalciferol-1-hydroxylase (1 alpha-hydroxylase), and parathyroid hormone (PTH)-stimulated adenylate cyclase activities were studied during 28 d of Ca depletion on a .08% Ca diet (LC) and 28 d of Ca repletion on a 3.75% Ca diet (HC). When laying hens on a HC diet were placed on a LC diet, plasma Ca and P, tibia breaking strength and ash percentage, and renal PTH-dependent adenylate cyclase activity were significantly depressed, but renal 1 alpha-hydroxylase activity was significantly stimulated. These changes were greater in the young hens than in the older hens; therefore an interaction between age and dietary Ca was found. These changes were of a lesser magnitude at 28 d of Ca depletion, probably due to the cessation of egg laying and to the desensitization of hormone-mediated function. 1 alpha-Hydroxylase activity was significantly less during the repletion period. The age effect was most pronounced for 1 alpha-hydroxylase, with the younger birds expressing significantly higher activity and ability to respond to hypocalcemia. There was a significant increase in kidney weights in Ca-deficient groups at 14 and 28 d of Ca depletion. It is concluded that younger hens have greater adaptive responses to Ca restriction than do older hens.

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Avian kidney function adapts during reproduction to provide the calcium required for eggshell formation. Adaptive changes in kidney function are 1) increased parathyroid hormone (PTH)-dependent adenylate cyclase activity; 2) elevated numbers of PTH receptors; and 3) increased synthesis of 1,25-dihydroxycholecalciferol. Because exogenous estrogen mimics these changes, this study explored the physiological role of estrogen in the regulation of kidney function by altering egg-laying status or levels of estradiol. In hens, treatment with the coccidiostatic drug, nicarbazin, led to cessation of egg laying with maintenance of the reproductive tract and of plasma estradiol and calcium. The PTH-dependent adenylate cyclase activity remained elevated (upregulated). However, when molting was induced by altering the photoperiod and diet, plasma estradiol, plasma calcium, and renal PTH-dependent adenylate cyclase activity all decreased. The depressed responsiveness to PTH was restored by administration of estradiol either during the molt or upon return to egg laying following the molt. When the estrogen antagonist, tamoxifen, was administered to laying hens, reproduction ceased and the PTH-dependent adenylate cyclase activity of renal membranes was decreased. In all three groups of nonlaying birds, the activity of kidney 25-hydroxycholecalciferol-1-hydroxylase was markedly decreased relative to that of laying hens irrespective of the amount of plasma estradiol. It was concluded that estrogen regulates the PTH-dependent adenylate cyclase system of avian kidney, whereas the activity of the 25-hydroxycholecalciferol-1-hydroxylase of kidney and thus, the synthesis of 1,25-hydroxycholecalciferol may be governed at least in part by the regulation of renal receptors for PTH by estrogen.

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Vitamin D-deficient (-D) Japanese quail embryos [from hens fed 1,25-dihydroxycholecalciferol (1,25-(OH)2D3)] die at Day 15 of incubation from severe calcium deficiency. Single doses of 125 ng cholecalciferol, 600 ng 24,25-dihydroxycholecalciferol [24,25-(OH)2D3], or 100 ng 1,25-(OH)2D3 were found to increase hatchability when injected into eggs prior to incubation. Cholecalciferol could be used from 125 to 1,250 ng per egg with no detrimental effects on hatchability, whereas single doses of 1,25-(OH)2D3 lower or higher than 100 ng per egg reduced hatchability. Injection of 125 ng cholecalciferol per egg supported the hatching of -D embryos when eggs were treated as late as 10 days of incubation. Sharply reduced hatchability occurred when cholecalciferol was injected at Day 11 or 12 of incubation. Experiments designed to evaluate the physiological state of 1-day-old quail treated with a single dose of cholecalciferol metabolites in ovo prior to incubation revealed that chicks had hypocalcemia, reduced total calcium content, and a six- to sevenfold increase in renal 25-hydroxycholecalciferol-1-hydroxylase activity. On the other hand, chicks from eggs treated with cholecalciferol were relatively normal. It appears that cholecalciferol administered in ovo is the compound of choice for supporting sustained development of the skeleton, mobilization of shell calcium, and prevention of hypocalcemia, probably because cholecalciferol is utilized slowly as needed to support development of the chick skeleton.

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Effects of vitamin D deficiency (-D) on mineral homeostasis were investigated in Japanese quail embryos. The -D embryos from 1,25(OH)2D3-fed hens became progressively calcium deficient, as documented by hypocalcemia and reduced calcium accumulation by the skeleton, yolk sac, and allantoic fluid. Plasma phosphate was progressively elevated between days 11 and 15. Increased calcium accumulation by the skeleton, yolk sac, and allantoic fluid occurred between days 12 and 15 in +D embryos. Phosphate and adenosine 3',5'-cyclic monophosphate (cAMP) concentrations of allantoic fluid increased in +D embryos during the period of shell calcium mobilization. Further increases in phosphate and cAMP excretion into allantoic fluid occurred in -D embryos, although no calcium was absorbed from the shell. Renal 25(OH)D-1-hydroxylase activity increased between days 11 and 13, whereas the adenylate cyclase response to parathyroid hormone was lost in -D embryos by day 14. These changes in renal function are indicative of secondary hyperparathyroidism in the -D embryos. Differentiation of villus cavity and capillary covering cells occurred in the chorionic epithelium of -D embryos, but eggshell calcium was apparently not absorbed. In contrast, 75% of the total body calcium of newly hatched (+D) chicks was obtained from the eggshell. Thus the dissolution and/or transport of eggshell calcium is dependent on vitamin D in quail embryos.

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Plasma melatonin profiles were determined in laying chickens maintained on either a 16L:8D or a 20L:4D light-dark cycle (LDC). The range of plasma melatonin concentrations was low during the light period (40-100 pg/ml) and higher during the dark period (150-390 pg/ml). Compared to the light period, plasma concentrations of melatonin were 4- to 5-fold higher (P less than 0.05) during the dark period. The amplitude of melatonin concentrations was greater when hens were held under a short dark period (4.6-fold, 20L:4D) than when hens were exposed to a 16L:8D LDC (3.8-fold). In the laying chicken, a broad peak in concentration of plasma melatonin was found in the dark period. It was different from that previously reported in the chick. Since the time of oviposition in the hen occurs in a limited period after the onset of darkness in a LDC, a modified physiological function of melatonin for birds of different ages may account for the difference in the nocturnal pattern of plasma melatonin. The elevated level of plasma melatonin in the dark period of a LDC is considered to be essential for regulating the time of oviposition in the laying chicken under a particular LDC.

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To compare the effects of using continuous (C) vs. intermittent (I) photoperiods with normal (24 hr) and a long but decreasing light-dark cycle (LDLDC) on production performance and egg quality, 240 White Leghorn hens of the University of Missouri-Columbia strain were individually caged in light-controlled rooms. Treatments applied at 21 weeks of age were light-dark cycles (LDC) of 25 hr gradually reduced to 23.5 hr with C or I photoperiods, and 24-hr LDC (controls); C or I photoperiods were gradually increased from 13.75 to 16 hr for the 25- to 23.5-hr LDC, and from 13.75 to 15 hr for the 24-hr LDC. Data were obtained on hen-day egg production, egg weight, egg mass, egg specific gravity, Haugh units, feed consumption, and feed efficiency. Hen-day egg production was significantly greater (P less than .01) for the combined C photoperiod treatments, while hens consumed significantly less (P less than .05) feed exposed to the combined I photoperiod treatments. Egg specific gravity was significantly better (P less than .05) for the LDLDC vs. the 24-hr LDC program with the difference being attributed to an increase (P less than .05) in initial egg specific gravity with the use of a 24-hr LDC. Egg weight, egg mass, Haugh units, and feed efficiency were not affected (P greater than .05) by LDC or photoperiod treatments.

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Progesterone production was compared in short-term cultures of turkey and fowl granulosa cells isolated from preovulatory follicles of different maturities. In both species cells from the most mature follicle produced the greatest amount of progesterone under stimulated conditions and in response to ovine or turkey LH, the latter being significantly more potent. Whereas basal production of progesterone was higher in turkey cells, the response to LH or cAMP stimulation was significantly greater in chicken granulosa cells both in absolute terms and particularly in relation to unstimulated levels. These species differences may reflect difference in the intensity of reproductive activity of the turkey and the domestic fowl selected for egg production.

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Embryos from turkey hens selected for high and low hatchability were blood sampled at 24, 25, 26, 27, and 28 days of incubation. The plasma was recovered and assayed for thyroxine (T4) and triiodothyronine (T3) to observe differences in plasma T3 and T4 concentrations relative to reduced hatchability. Plasma T3 did not differ significantly between the high and low hatchability groups, but plasma T4 concentrations were significantly greater during pipping at 26 and 27 days of incubation in the high hatchability group than in the low hatchability group. No differences were observed between the T3 and T4 ratios of the high and low hatchability groups. Oxygen consumption was significantly lower in the low hatchability group than in the high hatchability group. The data indicated that hypothyroidism may be a physiological factor limiting hatchability in domestic turkeys.

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Semen volume, seminal plasma color, protein concentration, and subfractions from 8 white semen (WS) and 8 yellow semen (YS) Large White turkeys were measured for 15 weeks. Average volume was .29 +/- .01 ml for WS and .32 +/- .02 ml for YS males. Plasma from WS was white and averaged 1.84 +/- .07 g/100 ml protein, whereas YS seminal plasma was yellow with 7.03 +/- .5 g/100 ml protein. Protein subfractions in WS and YS seminal plasma were qualitatively similar and consisted of prealbumin, albumin, alpha-1 and -2, beta-1, -2, and -3, and postbeta (gamma). The alpha proteins were more frequently seen in YS seminal plasma. The elevated protein of YS seminal plasma was due to an increased concentration of all proteins, with the possible exception of beta-3, with albumin contributing the most. Except for prealbumin and beta-3, the seminal proteins had the same electrophoretic mobility as counterpart blood proteins. Blood and seminal plasma protein concentrations were poorly correlated (+ .039; P less than or equal to .75). Blood protein concentrations from 68 toms ranged from 3.3 to 5.7 g/100 ml and averaged 4.2 g/100 ml; seminal plasma protein concentrations ranged from .93 to 12.8 g/100 ml. Nineteen percent of the males had YS with seminal plasma protein greater than 4.0 g/100 ml. The high correlation between intensity of the yellow color in YS seminal plasma and protein concentration (+ .76; P less than or equal to .01) indicates that semen quality of turkey breeders could be improved by selection on the basis of low seminal plasma protein concentration.

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Plasma total calcium to magnesium ratios were observed as an index of muscular activity during pipping and hatching of chick and poult embryos. No significant changes were observed in plasma calcium (Ca) or magnesium (Mg) concentrations, but the total Ca to Mg ratio increased significantly just prior to pipping. Lighting the incubator during the last 5 days of incubation in significantly increased plasma Ca and Ca:Mg ratios. Lighting also resulted in significantly better hatchability and less late embryonic mortality. An increased plasma Ca:Mg ratio may be a physiological mechanism to provide increased muscular activity for the embryo in breaking the shell and emerging from it.

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Male turkeys producing abnormal yellow-colored semen (YS) had hypertrophied epithelial cells in the ductuli efferentes. The cells were engorged with cytoplasmic, lipid-like (lipoid) droplets, a morphological abnormality found exclusively in this area of the epididymal region. The testes, epididymal region, ductus deferens, and abdominal fat were relatively yellow compared to turkeys producing normal white semen (WS). Adipose tissue within the abdominal cavity and lining the ductus deferens was more abundant in the YS producers. In addition to increased lipoid droplets, nonciliated cells of the ductuli epithelia contained larger and more numerous electron-dense lysosomal bodies than similar nonciliated cells in WS males. Resorption of morphologically normal and abnormal spermatozoa by the epithelia of the ductuli efferentes was prevalent in the YS males but was not observed in the WS turkeys. The seminal fluids in the epididymal region of the YS males contained abnormal spermatids, cellular debris, and increased amounts of electron-dense proteinaceous material.

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Blood samples were collected from turkey embryos during pipping and hatching, an age which corresponds to a time of elevated embryonic mortality. Samples were analyzed for erythrocyte counts (RBC), packed cell volume (PCV), hemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). An increase in RBC was significant (P less than .05) during piping and hatching. The PCV increased significantly (P less than .01) until pipping occurred and then declined significantly through hatching. The Hb concentration also increased significantly (P less than .05) as pipping and hatching occurred. The MCV declined significantly as development proceeded. Both MCH and MCH declined significantly (P less than .05) until the onset of pipping at which time both increased significantly (P less than .05) through hatching.

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Blood samples from turkey embryos taken at days 24 to 28 of incubation, a time of great embryonic mortality were analyzed for plasma calcium, magnesium, potassium, total plasma protein, lipid, and glucose concentrations. Plasma calcium increased significantly (P less than .05) until pipping, after which it declined until hatching. Plasma magnesium declined significantly (P less than .01) only at hatching. Potassium concentration declined significantly (P less than .01) as the hatched state approached. Plasma total protein concentration decreased until the onset of pipping, after which the concentration increased significantly (P less than .01) until hatching. Plasma total lipid concentrations decreased significant (P less than .01) during pipping, but the concentration remained constant while the poult emerged from the shell. Plasma glucose concentration increased significantly (P less than .01) prior to pipping and again at hatching.

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Local administration of small volumes of dilute detergents into the avian uterus (shell gland) induced premature oviposition within a few minutes with a success rate of over 90 percent. Indomethacin and cortisol blocked the action of detergents. Exogenous prostaglandins counteracted the inhibitory effect of indomethacin. It is suggested that detergents promote endogenous prostaglandin production which in turn induces oviposition. The possible significance of these observations in mammalian parturition is discussed.

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