Role of Acid-Base Balance in the Physiology of Egg Shell Formation

Ventilatory roll off during sustained hypercapnia is gender specific in pekin ducks

The objective of the present study was to examine the relative roles of peripheral versus central mechanisms in producing ventilatory adjustments in pekin ducks during prolonged (5 h) hypercapnia (5% inspired CO2), and to determine whether these adjustments differed between male and female ducks. After 20 min of CO2 exposure, intact ducks increased total ventilation (VE) 2.5-3-fold above control values, due to large increases (approximately 200%) in tidal volume (VT) and slightly smaller increases (approximately 140%) in breathing frequency (fR). This response was accompanied by respiratory acidosis (pHa fell from approximately 7.46 to approximately 7.41) and hypercapnia (PaCO2 increased from approximately 35 to approximately 40 Torr). In males, VE fell progressively thereafter due exclusively to a fall in fR, in parallel with a rapid partial recovery of pH (to 7.44) while PaCO2 continued to climb (to approximately 42 Torr). In females, VE remained elevated during hypercapnia, and no pH recovery occurred. This suggests that a respiratory decline resulting from acid-base compensation (probably due to HCO3- mobilization) occurred in males but not in females. Bicarbonate mobilization, and thus pH compensation, may have been reduced in females due to the CaCO3 requirements of eggshell formation. In males, the acute ventilatory response was reduced slightly by denervation of the carotid bodies or intrapulmonary chemoreceptors, but there was no effect of denervation of either receptor group on the responses to prolonged CO2. We conclude that pH compensation triggered by constant or increasing PaCO2, acting at central chemoreceptors, likely mediates the respiratory adjustments seen in male pekin ducks during hypercapnia. Furthermore, we suggest that this ventilatory response be considered a gender-specific hypercapnic ventilatory roll off, in the context of the various time domains of the hypercapnic ventilatory response.

Lack of response of laying hens to relative humidity at high ambient temperature

1. The effects of relative humidity (rh=40% to 70%) at high ambient temperature (Ta) on the performance of laying hens at different ages (8 to 10 months, Trial 1; and 16 to 18 months, Trial 2) was evaluated. Laying hens were exposed to 25 degrees C (control) for 3 weeks and thereafter acclimated for 1 week to 35 degrees C and 4 different rh. 2. Body weight declined significantly in young and older hens exposed to 60% or 70% and 70% rh, respectively: Food intake declined with increasing Ta, except in the case of older hens exposed to 60% rh, for which it remained relatively constant. Water consumption, however, increased with increasing Ta but the increase was significant in young hens exposed to 70% rh only. 3. Egg production was not affected by the changes in Ta. However, a decrease in egg production was observed in older hens exposed to 60% rh. 4. Egg weight (EW), shell weight (SW) and shell thickness (ST) were significantly reduced by exposure to elevated Ta, whereas % breakage significantly increased. In young hens, a response to rh was exhibited in ST which was significantly higher in hens exposed to the low rh (40% to 45%) than in those exposed to the highest rh (70% to 75%). 5. It can be concluded that Ta is the main environmental factor affecting young and older laying hens while the effect of rh is minor.

Evaluation of sodium bicarbonate, chloride, or sulfate with a coccidiostat in corn-soy or corn-soy-meat diets for broiler chickens

During the period from January to June, combined-sex broiler chickens were inoculated with coccidia via drinking water at 14 d of age. In a completely randomized design (eight replicate pens; 88 chicks per pen) using built-up litter, experimental diets contained monensin plus 0.20% dietary sodium bicarbonate (SBC), which provided 0.054% sodium and 0.144% bicarbonate. Treatment with SBC significantly improved coccidial lesion score, 45-d body weight, and feed efficiency compared with monensin alone. In a 2 x 5 factorial trial using built-up litter pens (eight replicate pens; 88 chicks per pen) vs. each ionophore alone, 0.20% dietary SBC with monensin significantly improved body weight, uniformity, and feed efficiency; 0.20% SBC with halifuginone, lasalocid, monensin, or salinomycin significantly reduced mortality; and 0.20% SBC with lasalocid, monensin, or salinomycin significantly increased breast meat yield. In a 2x4 factorial trial (12 replicate pens; 88 chicks per pen) on built-up litter, corn-soy and corn-soy-meat diets (higher potassium, lower chloride) with monensin were evaluated using 0.054% sodium from SBC, NaCl, or sodium sulfate decahydrate (SSD). With both diet types, SBC (0.20%) or NaCl (0.139% extra) significantly improved weight uniformity, feed efficiency, mortality, and breast meat yield; however, the SSD results were closer to controls. In a 21-d battery brooder test using similar diets and design (2x4 factorial; 4 replicate pens; 10 chicks per pen), SBC and NaCl significantly reduced coccidial lesion scores; SSD produced a significant, but weaker effect. Extra NaCl significantly increased water intake (approximately 37%), water excretion (approximately 27%), and litter moisture (approximately 22%) with both diet types. The SSD did not affect water intake.

Laying hens respond differently to high dietary levels of phosphorus in monobasic and dibasic calcium phosphate

A series of experiments were conducted to determine the relative acidogenicities of dietary chloride, phosphorus, and sulfate and their effects on shell quality. Calcium salts of these anions were added to a corn-soybean meal diet to provide supplemental levels of 150 to 450 meq/kg diet chloride, 150 to 600 meq/kg diet monobasic phosphate, 150 to 1,200 meq/kg diet dibasic phosphate, and 150 to 1,200 meq/kg diet sulfate. The results indicated that laying hens can safely tolerate up to 200 meq/kg diet supplemental chloride (.95% total chloride in the diet) and up to 450 to 600 meq/kg diet supplemental sulfate (2.16 to 2.88% added sulfate). Levels higher than these adversely affected shell quality and altered blood acid-base balance. Laying hens responded quite differently to phosphorus when it was supplied as monobasic or dibasic phosphate. Supplemental levels of 900 to 1,200 meq/kg diet dibasic phosphate (1.95 to 2.41% total phosphorus) did not have an adverse effect on performance and up to a supplemental level of 450 meq/kg diet (1.25% total phosphorus) did not affect shell quality. In contrast, performance was seriously impaired by a supplemental level of 150 meq/kg diet monobasic phosphate (1.02% total phosphorus in the diet). The results further indicated that phosphate in monobasic (but not in dibasic) form is a strong acidogenic anion and that most of its adverse effect on performance and shell quality can be ameliorated by alkaline salts of sodium or potassium bicarbonate. The relative acidogenicities of calcium salts of these acidic anions were as follows: phosphate (monobasic) > chloride > sulfate > phosphate (dibasic).

Responses of laying hens to diets containing up to 2% DL-methionine or equimolar (2.25%) 2-hydroxy-4-(methylthio)butanoic acid

Diets supplemented with up to .6% DL-Met (DLM) or .68% 2-hydroxy-4-(methylthio)butanoic acid (HMB, Alimet) acidify the urine and reduce the incidence of urolithiasis in pullets and laying hens. Excessive acidification potentially may reduce eggshell quality and bone mineralization by interfering with Ca metabolism and may severely challenge the liver and kidneys, which are the primary organs responsible for attenuating metabolic acidosis. To evaluate these possibilities, 30-wk-old Single Comb White Leghorn hens in full production (five hens per replicate, six replicates per diet treatment) were fed for 30 d a 15.7% CP corn and soybean meal-based control layer ration alone or supplemented with DLM (.5, 1, 1.5, or 2%) or equimolar HMB (.56, 1.13, 1.69, or 2.25%). None of the diets caused mortality or gross hepatic or renal damage. Hens fed diets supplemented with the highest levels of DLM and HMB exhibited significant reductions in feed intake, hen-day egg production, and liver mass and had lower plasma concentrations of alanine amino-transferase and isocitrate dehydrogenase when compared with hens fed the control diet. Kidney mass was not significantly affected by high levels of DLM or HMB, but plasma uric acid was significantly higher in hens fed 2% DLM compared with hens fed the control diet. The highest levels of DLM and HMB did not significantly alter total plasma Ca or inorganic phosphate concentrations, nor were percentage eggshell or femur mineralization (femur ash mass:defatted bone mass, femur ash mass:bone volume) significantly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalciuric response to dietary supplementation with DL-methionine and ammonium sulfate

Renal Ca and inorganic P (Pi) excretion were evaluated in Single Comb White Leghorn pullets reared on diets containing 1 or 3.5% Ca alone or supplemented with .6% DL-methionine or .53% ammonium sulfate. Plasma and urine samples were collected during a CONTROL period, and while 200 mM Ca was infused intravenously (Ca-LOADING). Excess Ca, whether supplied chronically in the feed or infused acutely into birds fed 1% Ca diets, significantly reduced glomerular filtration rates, effective renal plasma flow rates, and Pi excretion rates and significantly increased Ca excretion rates and urine pH. Birds fed diets supplemented with DL-methionine and ammonium sulfate maintained significantly lower plasma Ca concentrations during the CONTROL and Ca-LOADING periods than birds fed the respective 1 or 3.5% Ca basal diets. When compared with birds fed the respective 1 or 3.5% Ca basal diets, birds fed the 1% Ca diet supplemented with ammonium sulfate or the 3.5% Ca diet supplemented with DL-methionine had significantly higher absolute urinary Ca excretion rates during Ca-LOADING. Fractional Ca excretion during Ca-LOADING was significantly higher in birds fed 3.5% Ca supplemented with DL-methionine or ammonium sulfate than in birds fed the 3.5% Ca basal diet. These results indicate that DL-methionine and ammonium sulfate accelerated urinary Ca excretion and reduced Ca retention in the extracellular fluid. The hypercalciuric efficacies of DL-methionine and ammonium sulfate were revealed only when the filtered load of Ca was increased through intravenous Ca infusions.

Susceptibility of two commercial single comb White Leghorn strains to calcium-induced urolithiasis: efficacy of dietary supplementation with DL-methionine and ammonium sulphate

1. Susceptibility to calcium-induced urolithiasis was assessed in pullets of two commercial SCWL strains (A and B) reared together from 5 to 18 weeks of age on diets containing 10 g/kg calcium (normal calcium: NC) or 35 g/kg calcium (high calcium: HC). 2. Kidney damage was not observed in pullets reared on NC diets. For pullets fed on HC diets, strain A developed significantly greater kidney asymmetry, a higher incidence of gross kidney damage and a higher incidence of uroliths than strain B. 3. Supplementing the HC diet with 6 g/kg DL-methionine significantly reduced the incidence of calcium-induced gross kidney damage and urolith formation in both strains. Ammonium sulphate (5.3 g/kg) was significantly more effective than DL-methionine in reducing calcium-induced kidney damage. 4. Neither DL-methionine nor ammonium sulphate caused a measurable metabolic acidosis. Neither supplement consistently affected water consumption or manure moisture.

Liquid methionine hydroxy analog (free acid) and DL-methionine attenuate calcium-induced kidney damage in domestic fowl

To evaluate the possibility that kidney damage may be induced by the commercial practice of feeding high-Ca (HCa) prelayer rations, and to evaluate the protective efficacy of supplementing HCa diets with liquid methionine hydroxy analog free acid or DL-methionine, 12-wk-old female Single Comb White Leghorn pullets were fed one of the following corn-soybean meal-based diets until they reached 22 wk of age: normal-Ca (NC, 1% Ca); HCa (HC, 3.5% Ca); HCa supplemented with .34 or .68% liquid methionine hydroxy analog free acid (HC3A or HC6A); or HCa supplemented with .3 or .6% DL-methionine (HC3DL or HC6DL). The unsupplemented HC diet caused a significant reduction in kidney mass and a significant increase in the incidence of gross kidney damage and urolithiasis in pullets necropsied at 22 wk of age. Calcium-induced kidney damage was attenuated in a dose-response fashion by supplementing the HC diet with liquid methionine hydroxy analog and DL-methionine. None of the diets caused a significant metabolic acidosis. Plasma uric acid concentrations were not predictive of the extent of Ca-induced kidney damage. Analyses of glomerular size distributions indicated that subclinical or "hidden" kidney damage may not progressively develop into urolithiasis as hens mature. When compared with hens reared on the NC diet, rearing hens on the HC, HC3A, HC3DL, HC6A, or HC6DL diets did not consistently affect hen-day egg production, egg mass, eggshell mass, percentage eggshell, or bone mineralization.

Nutritional and environmental factors involved in egg shell quality of laying hens

1. Two experiments were conducted to assess the effects of lighting regime, dietary calcium source and sodium bicarbonate on production variables and egg shell quality of White Leghorn hens. In both experiments, hens were assigned to one of three lighting programmes that provided evening, morning or intermittent (midnight) lighting supplements in addition to natural daylight. Experimental diets used in the first study were formulated to contain (1) ground oyster shell flour, (2) limestone flour, or (3) and (4) the same +2/3 of the calcium source as hen-size oyster shell grit. The same 4 diets plus those containing hen-size limestone or hen-size limestone and oyster shells were used in experiment II. Additionally, diets in the first experiment contained either 0 or 10 g/kg sodium bicarbonate. 2. Hen-day egg production and food consumption were not affected by any of the experimental treatments. Hens fed on oyster shell diets or exposed to intermittent lighting regimes laid eggs of the highest specific gravity. Shell quality, as measured by specific gravity, was not affected by the addition of dietary sodium bicarbonate. 3. As expected, elevated temperatures (greater than 32 degrees C) significantly reduced egg shell quality. However, this effect was variable particularly in experiment II which used younger hens. 4. The shell quality of eggs from hens exposed to intermittent lighting in experiment II was significantly higher in each of the 4 sampling periods: morning (08.00-12.00), afternoon (12.00-16.00), evening (16.00-20.00) and night (20.00-08.00). 5. It is suggested that midnight lighting programmes provide a means of supporting egg shell quality of older laying hens during the summer months without a significant reduction in egg production.

Excess sodium bicarbonate in the diet and its effect on Leghorn chickens

1. A commercial 62-week-old layer flock experienced an acute drop in egg production and an increase in shell-less egg production within 2 days of consuming feed erroneously formulated to contain over 30 g/kg instead of 3 g/kg sodium bicarbonate (NaHCO3). Other symptoms included increased water consumption, diarrhoea and increased mortality associated with visceral gout. 2. An experiment was conducted to assess the responses of hens under controlled conditions. Twenty Dekalb XL Single Comb White Leghorn hens (50 weeks old) were placed in individual cages, having ad libitum access to water from trough waterers. Ten hens were fed the TEST (High NaHCO3) feed for one week (Test group), and ten hens remained on normal commercial layer ration (Control group). 3. Hens in the Test group had high water consumption and watery droppings, but egg production and mortality were not affected. Physiological evaluations indicated the Test feed caused metabolic alkalosis. Plasma sodium, urine pH and urinary sodium excretion were increased, and glomerular filtration rates were decreased in the Test group. 4. These physiological effects are consistent with known responses to excess sodium intake in domestic fowl. The reduced egg production and increased mortality caused by the Test feed under commercial conditions may be related to more severe dehydration experienced by hens in multi-bird cages supplied by cup-type watering systems.

CO2 and avian eggshell formation at high altitude

We tested the hypothesis that altitude-induced hypocapnia in hens reduces eggshell conductance to water vapor (GH2O). Seven laying hens (Gallus domesticus) native to 1200 m were chronically exposed to high altitude (3800 m), and then to high altitude with sufficient inspired CO2 to relieve hypocapnia (3800 m + CO2). Egg GH2O was measured gravimetrically, shell thickness was measured with a micrometer, and aggregate pore area was calculated from measured values using Fick's law. Comparing results at 1200 m (n = 118) and 3800 m (n = 102), GH2O was reduced from 13.9 +/- 0.2 to 12.6 +/- 0.2 mg/(d.Torr)(mean +/- SE), shell thickness was reduced from 0.297 +/- 0.003 mm to 0.287 +/- 0.003 mm, and calculated aggregate pore area per egg was reduced from 1.97 +/- 0.03 mm2 to 1.72 +/- 0.03 mm2. When hypocapnia was relieved at 3800 m + CO2 (n = 82), GH2O was reduced even further to 11.1 +/- 0.2 mg/(d.Torr), shell thickness increased to 0.305 +/- 0.003 mm, and aggregate pore area was reduced to 1.61 +/- 0.03 mm2. Based on these results we reject our hypothesis. We conclude that hypocapnia is responsible for thin eggshells at altitude. Other physiological stimuli must cause the reductions in eggshell GH2O and pore area.

Influence of sodium aluminosilicate, hydroxy-sodalite, carnegieite, aluminum sulfate, and aluminum phosphate on performance of commercial Leghorns

Experiments were conducted to determine if the high ion-exchange capacity of sodium aluminosilicate (ZA) marketed as ETHACAL Feed Component or its aluminum content or both are related to the beneficial effect of ZA on egg specific gravity (ESG). In Experiments 1 and 2, ZA was compared with hydroxy-sodalite (HS) and carnegieite, which have the same chemical formula as ZA but little or no ion-exchange capacity. Two levels of ZA (0 and 1.5% of the diet) and three levels of HS (0, .75, and 1.5%) were fed in Experiment 1. In Experiment 2, 0, .75, and 1.5% of ZA and carnegieite were fed. In Experiment 3, ZA, carnegieite, aluminum sulfate, and aluminum phosphate were fed at levels calculated to contain .148 and .101% aluminum. Criteria evaluated were ESG, egg production, feed consumption, and egg weight. Egg specific gravity was significantly improved by ZA in all experiments and was not affected by HS, carnegieite (Experiments 1 and 2), aluminum sulfate (.148% Al), or aluminum phosphate (Experiment 3). Carnegieite and aluminum (.101%) from aluminum sulfate increased ESG in Experiment 3. In Experiments 1 and 3, egg production and feed consumption were not influenced by various treatments. Carnegieite and ZA reduced egg production and feed consumption in Experiment 2. It was concluded that the ion-exchange capacity and aluminum content of ZA may contribute to its beneficial effect on ESG.

Response of commercial Leghorns to sodium aluminosilicate when fed different levels and sources of available phosphorus

Two experiments were conducted to elucidate possible explanations for the adverse interaction of sodium aluminosilicate (ZA) and low phosphorus on egg production. In Experiment 1, hens were fed available phosphorus at two levels (.40 and .31%) and from three sources (dicalcium phosphate, defluorinated phosphate, and meat and bone meal). Two levels (0 and .75%) of ZA were concomitantly fed with these treatments. In Experiment 2, hens were fed two levels (.30 and .20%) and two sources (dicalcium phosphate and defluorinated phosphate) of phosphorus with and without ZA (0 and .75%). In both experiments, egg production, egg specific gravity, feed consumption, and egg weight were measured. In Experiment 2, plasma sodium, potassium, chloride, total and free calcium, and phosphorus were also monitored. Results of both Experiments indicated that ZA significantly increased egg specific gravity; whereas, phosphorus level and source had no effect on egg specific gravity. Egg production was influenced by ZA level, phosphorus source, and phosphorus level with significant phosphorus source by phosphorus level interactions. In Experiment 1, ZA reduced egg production at the higher phosphorus level when dicalcium phosphate or defluorinated phosphate was used but not at the lower phosphorus level. Egg production was not influenced by ZA when meat and bone meal was the source of phosphorus. In Experiment 2, ZA reduced egg production more at the lowest level of phosphorus and more when the phosphorus source was defluorinated phosphate than when it was dicalcium phosphate but the interaction was not significant. Sodium aluminosilicate had no influence on egg weight, but it did reduce feed consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of environmental stress on the ascorbic acid requirement of laying hens

An experiment with a factorial arrangement of treatment (3 by 2 by 2 by 2) was conducted to determine the effect of ascorbic-acid supplementation (0, 100, and 200 ppm) on the performance of two commercial layer strains housed at a density of either 3 or 4 birds per cage and relative humidities (RH) of 40% or 60%. The hens were subjected to a continuous heat stress of 31.1 degrees C for the 3-mo experimental period. As a comparison with an unstressed control group, an additional group of hens was housed at 23.9 degrees C and 40% RH and was fed the diet without ascorbic-acid supplementation. Mortality was reduced by ascorbic-acid supplementation. Shell weight per unit surface area showed a small increase with the added ascorbic acid. Values (in Haugh units) were increased by ascorbic-acid supplementation at the 200 ppm level and by the lower relative humidity. The higher RH reduced egg production by 4.16% and changed feed efficiency from 2.29 to 2.45 g of feed intake per gram of egg mass. There were differences in blood pH, blood CO2, blood HCO3-, and blood and adrenal ascorbic-acid levels due to the housing temperature. The higher RH produced blood-chemistry changes that were typical of respiratory alkalosis, which has been shown to occur in layers at high temperatures. Higher cage density, on the other hand, showed no change in the HCO3 level; but blood pCO2 was increased while blood pH was decreased. These results demonstrate that ascorbic-acid supplementation can be effective in reducing laying-hen mortality due to environmental stress and has small influences on egg quality.

Order of exposure to high dietary calcium and gray strain infectious bronchitis virus alters renal function and the incidence of urolithiasis

Experiments were designed to determine if Gray strain infectious bronchitis virus (IBV) infection increases the incidence of urolithiasis type kidney damage when the urine is already high in Ca and relatively alkaline due to a high Ca-low available P diet (i.e., layer ration). In addition, experiments were conducted to determine the effects of Gray strain IBV on pullet renal function of 6 and 14-wk-old pullets at 2, 5, and 10 days postinoculation (PI). Blood gas parameters were measured to determine the mechanism by which layer ration decreases hydrogen ion concentration [( H+]). Urine flow rate, glomerular filtration rate, electrolyte excretion (Na, K, Ca, P), free water clearance, urine osmolality, urine [H+], and renal plasma flow (para-aminohippuric clearance) were measured to assess renal function. Gray strain IBV increased urine [H+] and decreased renal plasma flow in 6-wk-old pullets, and induced a diuresis in 14-wk-old pullets between 5 and 10 days PI. The layer ration increased Ca excretion and induced a metabolic alkalosis, thus decreasing urine [H+] and causing urolith formation. Feeding layer ration followed by Gray strain IBV infection had an additive effect on the incidence of urolithiasis and gross kidney damage. Gray strain IBV infection 8 wk prior to feeding layer ration did not induce urolithiasis. The results suggest that the additive effect of Gray strain IBV on the incidence of urolithiasis is probably due to tubular damage rather than direct changes in renal function parameters.

Effect of dietary acidification and alkalinization on urolith formation and renal function in Single Comb White Leghorn laying hens

One of the major causes of mortality in poultry is urolithiasis. Although two of the major causes of urolithiasis have been defined, active and preventative treatments for this disease have not been extensively field tested. Previous research demonstrated that a diet acidified with NH4Cl was effective in preventing the formation of uroliths in 16-wk-old pullets. In the present study, experiments were designed to evaluate the effects of dietary acidification and alkalinization on preformed uroliths in mature laying hens. Urolithiasis was induced by feeding excess dietary Ca (in commercial layer ration) during pullet growout (6 to 18 wk of age) and during the early laying period (18 to 32 wk of age). At 32 wk of age birds were randomly divided into three diet treatment groups: a normal layer ration group, an acidified layer ration group (1% NH4Cl added); and an alkalinized layer ration group (1% NaHCO3 added). Each group received the respective diets until 52 wk of age, when the experiment was terminated. Blood gas analysis at 44 wk of age demonstrated that hens fed the acidified diet had significantly higher blood H+ concentrations, lower blood bicarbonate concentrations, and lower total blood carbon dioxide levels than hens fed the alkalinized layer ration. At 52 wk of age, hens fed the acidified layer ration had higher urinary H+ concentrations, higher blood H+ concentrations, and lower blood HCO3 and total CO2 concentrations than hens fed the normal and alkalinized layer rations. The acidified layer ration group had no uroliths present in their ureters (0% urolithiasis), whereas the normal and alkalinized layer ration groups had 8.3 and 13.1% incidences of urolithiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Eggshell quality as influenced by sodium bicarbonate, calcium source, and photoperiod

The effects of Ca source (limestone or a mixture of one-third limestone and two-thirds oyster shell), NaHCO3 (0 or .5%) and feeding photoperiod (16 or 24 hr) were studied in a 16-week experiment involving 240 Hy-Line W-36 Leghorn hens, 25 weeks of age. Neither egg production (percent hen-day and egg mass, kg egg/bird per 16 weeks) nor feed conversion ratio (kg feed per kg egg) were significantly (P greater than .05) affected by dietary treatment or photoperiod. However, extending the photoperiod to 24 hr significantly (P less than .05) increased feed consumption with a consequent increase in egg weight (P less than .01). Feeding oyster shell in combination with limestone significantly (P less than .05) improved specific gravity of eggs, whereas dietary NaHCO3 significantly (P less than .01) improved elasticity of the egg shell as measured by deformation. Eggshell quality was improved by increasing the photoperiod to 24 hr and was most pronounced when hens were fed diets supplemented with .5% NaHCO3 and limestone as the only source of Ca.

Effect of dietary acidification on kidney damage induced in immature chickens by excess calcium and infectious bronchitis virus

Experiments were designed to evaluate the effect of dietary acidification on the development of kidney lesions induced by excess dietary calcium (Ca) and Gray strain infectious bronchitis virus (IBV). Specific pathogen-free (SPF) chicks and SPF chicks inoculated with Gray strain IBV were fed one of three diets: a commercial pullet grower ration (1% Ca); a commercial layer ration (3.25% Ca); or layer ration plus .5% ammonium chloride (acidified layer ration). Gray strain IBV significantly reduced total kidney weights in males, reduced total kidney weight as a percentage of body weight in males, increased the number of gross kidney lesions, and decreased the number of filtering nephrons when compared with uninoculated birds when both groups were fed the grower ration. The layer ration induced a 60% incidence of kidney lesions, caused a significant increase in kidney weight asymmetry ratios, and caused a 25% reduction in the number of filtering nephrons. Acidifying the layer ration significantly reduced the incidence of gross kidney lesions and reduced kidney weight asymmetry ratios, but did not prevent Ca-induced reductions in filtering nephrons.

Effects of thermal-induced respiratory alkalosis on blood ionized calcium levels in the domestic hen

An experiment was conducted to determine the change with time in the blood ionized calcium concentration of hens exposed to an acute heat stress. Five hens were surgically fitted with carotid artery cannulae and placed in cages inside a temperature-controlled chamber. Blood samples were drawn before (23 C), during (35 C), and after (23 C), a 3-hr heat-stress exposure. Whole blood ionized calcium, blood gas, plasma pyruvate, and lactate were determined. Respiratory alkalosis developed 1 hr after the start of heat exposure (35 C). Approximately 1 hr later, there was a concomitant decline in blood pH as plasma lactate and pyruvate concentration increased (P less than .05). In addition, the blood ionized calcium level was reduced (P less than .05) by 19% and was negatively correlated (P less than .05) with plasma pyruvate (-.77) and lactate (-.81). These results suggest that changes in acid-base balance during heat stress reduce the blood ionized calcium level, which may in turn limit the availability of calcium for egg shell formation.

Arterial blood gas, pH, and bicarbonate values in laying hens selected for thick or thin eggshell production

Bicarbonate, pH, carbon dioxide partial pressure (pCO2), and oxygen partial pressure (pO2) were measured in blood samples collected anaerobically from the brachial arteries of domestic fowl from lines selected for thick (TK) or thin (TN) eggshell production. The blood values of TK and TN hens were compared 6 hr prior to oviposition and continued at 2-hr intervals until 10 hrs postoviposition. Percent shell values were measured for eggs laid 2 days prior to and during blood sampling. Hens with TK shells had significantly (P less than .001) higher percent shell values than hens with TN shells. The measured blood parameters (bicarbonate, pH, pCO2, and pO2) did not differ significantly (P greater than .05) when TK and TN hens were compared at the time of oviposition. However, between 2 and 6 hr postoviposition, TN hens had significantly lower blood pH, pO2, and bicarbonate than did TK hens. Arterial pCO2 tended to be higher in TN hens than in TK hens, but this difference was significant only at 6 hr preoviposition. These results show that TN hens develop metabolic acidosis relative to TK hens during the first 6 hr postoviposition.

The effect of tap water, carbonated water, sodium bicarbonate, and calcium chloride on blood acid-base balance in cockerels subjected to heat stress

Twenty Hubbard cockerels each weighing 2.4 kg were surgically fitted with plastic cannulae in the carotid artery and crop. A solution of either tap water (TW), carbonated water (CW), 2% sodium bicarbonate (HCO3-), or 3.5% calcium chloride (CaCl2) with pH of 7.8, 5.2, 8.0, and 7.4, respectively, was infused into the crop at .41 ml X min-1 X kg body weight (BW)-1. Blood pH, carbon dioxide partial pressure (PCO2), and respiratory rate (RR) were measured at 15-min intervals during a 90-min thermoneutral period (25 C) followed by a 90-min heat stress (37 C). Polypnea occurred in all treatments in the 37 C environment. Infusion of HCO3- increased blood pH throughout the thermoneutral and heat stress periods, and CaCl2 infusion decreased blood pH throughout the experimental periods. At thermoneutral temperature, TW and CW infusions did not affect blood pH or PCO2. During heat stress, blood pH increased in TW and CW treatments; change and final pH were significantly lower (P less than .05) for CW- compared with TW-infused birds. Although blood PCO2 decreased in all treatments with the imposition of heat stress, blood PCO2 was significantly greater (P less than .05) in birds infused with HCO3- at the end of the heat-stress period. The results demonstrate that CW treatment produced a more favorable acid-base balance during acute heat stress than TW by reducing blood pH change during thermal polypnea. Also, high levels of NaHCO3 and CaCl2 intake can produce abnormal acid-base equilibrium conditions during the heat stress-induced respiratory alkalosis.

Dietary interaction of phosphorus with sodium from either chloride or bicarbonate affects laying hen performance

Experimental diets consisting of two levels of total phosphorus (.30 and .75%) and three different treatments of supplemental sodium (.35% NaCl, 1.40% NaCl, and .35% NaCl plus 1.50% NaHCO3) were fed in a 2 X 3 factorial arrangement to laying hens for 16 weeks. The latter two treatments of sodium were designed to supply the same level of sodium (.55%) from different chemical forms. Hens fed .30% phosphorus laid significantly (P less than .01) less eggs than those fed .75% phosphorus. A highly significant (P less than .01) interaction was found between phosphorus and sodium treatments. The high level of sodium from either chloride or bicarbonate decreased egg production at the lower level of phosphorus and increased it when the higher level of phosphorus was fed. Sodium bicarbonate affected egg production more strongly than sodium chloride did. There were no significant treatment effects on egg weight and egg shell weight. Addition of sodium bicarbonate to the low phosphorus diet significantly (P less than .05) decreased feed consumption of the hen. Supplemental sodium bicarbonate with either level of dietary phosphorus significantly (P less than .05) increased percent nitrogen retention of the hen, but excessive sodium chloride did not.

25-hydroxycholecalciferol-1-hydroxylase activity in heat stressed laying hens

The activity of 25-hydroxycholecalciferol-1-hydroxylase was assayed in heat stressed laying hens fed a 3.5% calcium diet with either .625% or .925% phosphorus. The activity of this enzyme in the heat stressed birds was higher than in the control birds (P less than or equal to .07). The phosphorus content of the diets had no effect on enzyme activity.

Thermal panting and respiratory alkalosis in the laying hen

1. Changes in respiratory rate (f), rectal temperature (Tr) and blood acid-base values were measured in laying hens exposed to ambient temperatures (Ta) of 32, 35, 38 or 41 degrees C. 2. At Ta 32 degrees C there was no panting. At Ta 35 degrees C panting occurred without any increase in Tr but there was a slight alkalosis (pH 7.55). 3. At Ta 38 degrees C Tr increased and panting was accompanied by moderate alkalosis (pH 7.58). 4. At Ta 41 degrees C Tr increased considerably and severe alkalosis developed (pH 7.65). 5. From the relation between Tr, f and pH it is concluded that some degree of alkalosis is a normal response to panting in the laying hen.

Studies on the avian shell gland during egg formation: mucosal intracellular pH

1. The intracellular pH and the extracellular fluid volume of the shell gland mucosa were determined. 2. The pH value varied little during egg formation, the overall mean being 7.11 +/- 0.02 (n = 34). 3. The lowest pH, 7.01, was found 10 h after oviposition and the highest, 7.22, 18 h after oviposition.

Studies on the avian shell gland during egg formation: aqueous and electrolytic composition of the mucosa

The intracellular composition of the avian shell gland mucosa was studied at six stages of egg formation. 2. Total water content of the mucosa before shell calcification was 4-8 kg/kg dry weight (dw) and rose to 6-6 kg/kg dw during shell formation; 60% of the increase was intracellular and 40% extracellular. 3. The potassium concentration of the mucosa remained constant during egg formation. 4. Chloride was removed constantly from the mucosal cells during egg formation. 5. A model was constructed for the glandular cells which depicts them as primarily NaHCO3-secreting cells towards the luminal side and HCl-secreting cells towards the serosal side, their main function being to provide CO2/3- for shell formation. In this model, the columnar mucosal cells are responsible for the calcium used in shell formation.

Calcium transport across avian uterus. III. Comparison of laying and nonlaying birds

Transepithelial calcium fluxes were measured across isolated uterus of laying, nonlaying, and molting quail under conditions where no electrochemical difference existed across the tissue. Net uterine transfer of calcium in molting and nonlaying birds occurs in the secretory direction and is approximately one-fifth the value obtained for laying birds. The carbonic anhydrase enzyme activity of uteri from laying birds is twice that of uteri from molting birds and five times greater than that of uteri from nonlaying birds. When measured in the presence and absence of 2-mercaptoethanol or dithiothreitol, no statistical difference exists in uterine carbonic anhydrase activities of laying birds or the inhibitory effect of acetazolamide. These results indicate that nonlaying and molting quail secrete calcium at a rate much lower than that of laying quail and that net uterine transfer of calcium exhibits varing degrees of dependence on bicarbonate ion in laying, nonlaying, and molting birds. Carbonic anhydrase data sugges that the activtiy of this enzyme in the quail uterus may be related to uterine calcium secretion.

Reproductive tissue activity in hypothyroid or heat stressed hens

The ability of the reproductive tract of the White Leghorn hen under heat stress or methimazole thyroid blockage to assimilate 32P was examined. Both treatments increase the uptake of 32P by the shell gland and egg shell but only heal stress increases 32P uptake by the ovaries and reduces shell thickness. The greater shell thinness under the heat stress is related to an increased deposition of phosphate in the shell. Gilbert (1967) has reported an increased serum calcium, due to calcification inhibitions by phosphate, leading to an increased gonadotropin secretion. Thyroid blockage appears to stimulate TSH and gonadotropin LH secretion but in the absence of phosphate inhibition of calcification shell thickness is not affected. It is also speculated that hypothyroidism does not stimulate FSH secretion and therefore ovarian tissues is not activated by this condition.

Acid-base balance, plasma electrolytes and production performance of adult turkey hens under conditions of increasing ambient temperature

Turkey hens were exposed to stepwise increases in ambient temperature from 21 degrees C. to 25 degrees C. to 30 degrees C. to 35 degrees C. at two-week intervals. Dietary calcium levels to 1.54, 2.01 and 2.48 percent were fed. Acid-base balance, plasma electrolytes and production performance were studied. The temperature increase caused a significant (P less than 0.05) decrease in plasma sodium, calcium, and magnesium, and in egg production, shell thickness and egg weight and a significant (P less than 0.05) increase in plasma potassium. There was no significant change in the acid-base balance of the blood as measured by blood PO2, PCO2 and pH. Egg production was not significantly correlated to blood gas activitelated to plasma calcium and magnesium levels. Dietary calcium levels had no influence on the parameters measured.

Effects of short term phosphorus deprivation on laying hens

An experiment was conducted to determine the effects on laying hens of ingestion of a phosphorus deficient diet for 6, 9, or 21 days. Four experimental groups consisting of 3 replicates of 5 Leghorn pullets averaging 90 percent egg production were maintained in individual cages. A diet containing corn, soy, and meat and bone meal was formulated to contain 0.39 percent total P on a 90 percent dry matter basis (LP). A normal P diet (NP), 0.64 percent total P, was obtained by supplementation with an inorganic P source. Group 1 (Control) was fed the NP diet for 21 days. Groups 2, 3 and 4 were fed the LP diet for 6, 9, and 21 days respectively. Groups 2 and 3 resumed consumption of NP diet after 6 and 9 days. Individual egg production and egg weight were recorded daily. Individual hen determinations of serum P, g. shell/cm.2 surface area, and feed consumption by replicate were made at 3 or 4 day intervals. The serum P of Group 1 averaged 5.01 +/- 0.31 mg./100 ml. over the 21 days. Serum P was significantly reduced after 3 days of consuming the LP diet. Serum phosphorus of Groups 2,3, and 4 were 2.95 +/- 0.18, 3.03 +/- 0.24, 3.13 +/- 0.32 mg./100 ml. respectively after 6, 9, and 21 days of consuming the LP diet. Serum P returned to control levels within 4 days after resumption of the NP diet by Groups 2 and 3. There were no differences in feed consumption, egg production nor any detrimental effects on egg weight or shell calcification despite the low serum P. Body weight gain of the hens fed the phosphorus deficient diet for 21 days was significantly reduced. At the end of the experiment femur density was determined; the hens which had consumed the phosphorus deficient diet for 21 days had reduced femur density (osteoporous) compared to the control group or the hens fed the phosphorus deficient diet for only 9 days. It is concluded that pullets in 90 percent production can tolerate this low P diet for at least 9 days without apparent detrimental effects.

Effects of PCBs, DDT, and mercury compounds upon egg production, hatchability and shell quality in chickens and Japanese quail

Dietary polychlorinated biphenyls (PCBs), DDT and related compounds, in well controlled experiments, produced no detrimental effects upon egg shell quality in Single Comb White Leghorm chickens or in Japanese quail. PCBs caused some decrease in egg production and a drastic reduction in hatchability in chickens, but not in Japanese quail. Inorganic mercury as HgSO4 or HgCl2, at dietary levels up to 200 p.p.m. of Hg, had only small effects, if any, upon egg production, hatchability, shell quality, morbidity and mortality. However, methyl mercury chloride at levels which provided 10 or 20 mg. of Hg per kg. of diet caused severe effects upon egg weight, egg production, fertility, hatchability, egg shell strength, morbidity and mortality. The results of these experiments demonstrate that the decrease in egg shell quality which has occurred in eggs of White Leghorn hens over the past three decades is not due to contamination of commercial feeds with DDT or its derivatives, or with PCBs. The extent to which environmental contamination with methyl mercury is responsible for decreased egg shell strength in commercial laying hens, and possible synergistic relationships between methyl mercury, DDT, DDE and PCBs in reducing egg production, hatchability and shell strength, remain to be determined.