Influence of calcium and environmental temperature on performance of first-cycle (phase 1) commercial leghorns

Effects of ecofriendly synthesized calcium nanoparticles with biocompatible Sargassum latifolium algae extract supplementation on egg quality and scanning electron microscopy images of the eggshell of aged laying hens

In the present study, 200 Brown commercial egg-type layers (60 wk old) were used to study the effects of different levels of ecofriendly synthesis of calcium (Ca) nanoparticles (0.0, 0.50, 1.0, and 1.5 g/kg diet) with biocompatible Sargassum latifolium algae extract (SL-CaNps) on exterior egg quality traits, electronic microscopic view of eggshells, Ca and phosphorus (P) retention, serum Ca and P concentrations, and the histology of the uterus. Hens fed with dietary SL-CaNps powder had higher egg weight and shell weight % values than those of the control group. All SL-CaNps treatment groups had the greatest values of shell weight per unit surface area and shell thickness. Dietary supplementation of SL-CaNps at graded levels up to 1.5 g/kg diet had higher serum Ca and inorganic P levels than that of the control. Laying hens fed with SL-CaNps-added diets had beneficial effects on shell ultrastructure in terms of well-developed palisade and mammillary layers. The numbers of apical cells along the branched tubular gland were greater in SL-CaNps-treated groups than those of control. Conclusively, supplementing SL-CaNps powder up to 1.5 g/kg to the diet of laying hens improved eggshell thickness, shell weight% and shell weight per unit surface and has no adverse effect on their eggshell quality or electronic microscopic view of their eggshell.

Influences of low level of dietary calcium on bone characters in laying hens

Cage layer fatigue (CLF), which is commonly caused by calcium deficiency in the feed, leads to loss of structural bone and increase of bone fragility. In order to investigate the influence of low-calcium diets on bone quality and strength, histopathology, and egg quality, 72 laying hens were randomly allocated to 2 groups at 22 wk of age and received low calcium and control calcium until 34 wk, respectively. Egg production, feed consumption, BW, and egg quality were measured throughout. Bone mineral density, bone biomechanical properties, and histomorphology of femurs and tibias were assessed after birds were sacrificed in 26, 30, and 34 wk. The results showed that low-calcium (1.5%) diets decreased BW, feed consumption, and egg production. The broken eggs rate increased, and the eggshell strength and thickness were lower in treated birds than those in control birds at 30 wk and 34 wk. Femoral and tibial bone index and bone mineral density were lower, cortical thicknesses were thinner, and bone length were shorter over time when birds are in a low-calcium diet than those in control birds. In biomechanical properties, the values of stiffness, Young's modulus, and breaking strength were lower in both femurs and tibias in low-calcium hens at 30 wk and 34 wk than those in bones of control hens. In histomorphology of bone, the cortex turned thinner and there were more cavities in cortex and cancellous bone; the trabecular bone network was fewer, thinner, less cohesive, and generally fragmented; and trabeculae were less well-connected in low-calcium birds. Some cell nuclei in cancellous bone disappeared, and vacuolation was observed in bone cells. There appeared osteoid in cortex bone and cancellous bone in tibias. It was concluded that low-calcium diets could facilitate the development of osteoporosis characterized by an increase of osteoid and loss of structural bone and decrease the values of bone quality and strength, accompanied with a decrease in egg production and egg qualities, which may elucidate the developing mechanism of CLF.

Estimation of calcium requirements for optimal productive and reproductive performance, eggshell and tibial quality in egg-type duck breeders

Optimizing the dietary calcium (Ca) level is essential to maximize the eggshell quality, egg production and bone formation in poultry. This study aimed to establish the Ca requirements of egg-type duck breeders from 23 to 57 weeks of age on egg production, eggshell, incubation, tibial, plasma and ovary-related indices, as well as the expression of matrix protein-related genes. Totally, 450 Longyan duck breeders aged 21 weeks of age were allotted randomly into five treatments, each with six replicates of 15 individually caged birds. The data collection started from 23 weeks of age and continued over the following 35 weeks. The five groups corresponded to five dietary treatments containing either 2.8%, 3.2%, 3.6%, 4.0% or 4.4% Ca. The tested dietary Ca levels increased (linear, P <0.01) egg production and egg mass, and linearly improved (P <0.01) the feed conversion ratio (FCR). Increasing the dietary Ca levels from 2.8% to 4.4% increased (P <0.01) the eggshell thickness and eggshell content. The tested Ca levels showed a quadratic effect on eggshell thickness and ovarian weight (P <0.01); the highest values were obtained with the Ca levels 4.0% and 3.6%, respectively. Dietary Ca levels affected the small yellow follicles (SYF) number and SYF weight/ovarian weight, and the linear response (P <0.01) was significant vis-à-vis SYF number. In addition, dietary Ca levels increased (P <0.05) the tibial dry weight, breaking strength, mineral density and ash content. Plasma and tibial phosphorus concentration exhibited a quadratic (P <0.01) response to dietary Ca levels. Plasma calcitonin concentration linearly (P <0.01) increased as dietary Ca levels increased. The relative expression of carbonic anhydrase 2 in the uterus rose (P <0.01) with the increment of dietary Ca levels, and the highest value was obtained with 3.2% Ca. In conclusion, Longyan duck breeders fed a diet with 4.0% Ca had superior eggshell and tibial quality, while those fed a diet with 3.6% Ca had the heaviest ovarian weights. The regression model indicated that the dietary Ca levels 3.86%, 3.48% and 4.00% are optimal levels to obtain maximum eggshell thickness, ovarian weight and tibial mineral density, respectively.

Effects of Different Dietary Calcium Levels on the Performance, Egg Quality, and Albumen Transparency of Laying Pigeons

Simple Summary

The transparency of pigeon egg albumen is a special phenotypic trait that different from other poultry eggs, and calcium is one of the main factors. This experiment aimed to study the effects of added dietary Ca on production performance, egg quality, and albumen transparency. It will guide producers on how to feed their laying pigeons and provide a scientific basis for special feed research and the development of laying pigeons with transparent eggs.

Abstract

In order to confirm the dietary calcium (Ca) requirement to keep a balance of the production performance and the albumen transparency, the study examined the effects of different dietary Ca levels on the production performance, egg quality, and albumen transparency of laying pigeons. 1080 pigeon pairs were randomly allocated into six treatment groups, each consisting of six replicates of 30 pigeon pairs per treatment. Ca levels of 0.60, 0.90, 1.20, 1.80, 2.40, and 3.00% were fed. The results showed that the laying rate, average egg weight, and feed to egg ratio were significantly influenced by Ca levels (p < 0.05). Albumen percentage, albumen height, Haugh unit, and eggshell thickness at 8 w and 16 w were significantly influenced by Ca levels (p < 0.05). The L*, a*, b*, and c* values of cooked albumen at 8 w and 16 w were all significantly influenced by Ca levels (p < 0.05). After 16 w of feeding different Ca levels, the percentage of transparent eggs had an early increasing and later decreasing trend. In conclusion, taking the transparency of pigeon eggs as an assessment index and considering production performance secondly, the optimal level of dietary Ca for laying White King pigeons is 0.90%.

Medullary bone attributes in aged Lohmann LSL-lite layers fed different levels of calcium and top-dressed 25-hydroxy vitamin D3

Structural bone depletion over the course of lay cycle predisposes hens to skeletal problems. We investigated the effects of dietary calcium (Ca) and top-dressed 25-hydroxy vitamin D3 (25OHD3) on attributes [relative weight, ash content (AC), and ash concentration (ACN)] in whole ulna, femur, tibia, and subparts of femur and tibia (epiphysis, medullary, and cortical) in 74-wk-old Lohmann LSL-lite layers. Four levels of Ca (3.0%, 3.5%, 4.0%, and 4.5%) and three levels of 25OHD3 (0, 69, and 138 μg kg−1) were tested. All diets had basal level of 3300 IU of vitamin D3 kg−1. Eighty-four, 74-wk-old hens were placed in individual cages, and 13 spare hens were sacrificed for baseline samples. Diets (n = 7) were fed to 81 wks of age, and hens were sacrificed for bone samples. There were no (P > 0.05) diet effects on whole bone attributes. Interaction (P < 0.05) between Ca and 25OHD3 on femur subparts was such that 25OHD3 linearly increased medullary ACN and concomitantly decreased cortical ACN at all Ca levels. In tibia, 25OHD3 (P < 0.05) increased AC and ACN in medullary and reduced these parameters in cortical. The results suggested that subparts and not whole medullary bone attributes are more amenable to dietary interventions in aged hens.

Effects of Dietary Calcium Levels on Productive Performance, Eggshell Quality and Overall Calcium Status in Aged Laying Hens

This study was conducted to investigate the effects of diets with varying levels of calcium on egg production, shell quality and overall calcium status in aged laying hens. A total of five hundred 70-wk-old Hy-Line Brown layers were divided five groups and fed one of the five experimental diets with 3.5%, 3.8%, 4.1%, 4.4%, or 4.7% Ca, for 10 weeks. There were no significant differences in feed intake, egg production and egg weight among groups. The cracked eggs were linearly reduced as dietary Ca levels increased to 4.7% (p<0.01). A significant linear improvement for eggshell strength and thickness were determined with increasing dietary Ca levels (p<0.01). The contents of serum Ca and phosphorus were not affected by dietary Ca levels. With increase in dietary Ca levels, the tibial breaking strength slightly increased. There were no significant differences in the tibial contents of ash, Ca and phosphorus among groups. In conclusion, eggshell quality, as measured by appearance, strength and thickness of eggshell, were influenced by dietary Ca content as expected (p<0.05). These results suggested that aged laying hens require relatively higher level of Ca than required levels from current Korean feeding standards for poultry.

Effect of calcium with and without probiotic, lactose, or both on organ and body weights, immune response and caecal microbiota in moulted laying hens

A total of 72 laying hens were used to investigate the effect of probiotic and lactose on body weight loss, tibia ash, antibody production against sheep red blood cell (SRBC), heterophile-to-lymphocyte (H/L) ratio and gut microbiota in a common moulting method for 14 d. Hens were randomly allocated to 6 experimental groups consisting of (i) full feed (FF), (ii) feed withdrawal (FW), (iii) FW with calcium (Ca), (iv) FW with Ca and offering 7 g/lit lactose in drinking water (CaL), (v) FW with Ca and offering 1 g/lit probiotic in drinking water (CaP), and (vi) FW with Ca and offering a mixture of lactose and probiotic in drinking water (CaLP). The results showed body weight loss in all FW groups were more than 25% that was significantly higher than FF group (p < 0.05). The relative organ weights of hens in FW groups were lower than FF group; especially, it was significant for liver and ovary (p < 0.05). No significant difference was observed between all groups for tibia ash. The highest H/L ratio was related to FW group and offering Ca and lactose numerically and probiotic alone significantly resulted in decrease of this ratio (p < 0.05). The results also showed no significant difference for antibody production against SRBC among experimental groups. The highest coliform bacteria numeration observed in FW group and lactose could significantly reduce this population (p < 0.05). Lactic acid bacteria (LAB) numeration demonstrated a significant difference among treatments, so that FF hens had higher LAB than others (p < 0.05). In addition, FW moulted hens had significantly lower LAB compared to other moulted hens (p < 0.05), except for Ca group. In conclusion, probiotic and lactose was effective in maintaining caecal microbiota balance and improving immunity in hens exposed to moulting.

Effects of dietary energy and calcium levels on performance, egg shell quality and bone metabolism in hens

This study investigated the effects of dietary energy and calcium levels on laying performance, eggshell quality and bone metabolism of layers. One hundred and sixty-two 19-week-old Hy-Line brown laying hens in 54 battery cages were allocated to one of nine dietary treatments with control, middle and high levels of energy (11.50, 12.68 and 13.37 MJ/kg, respectively) and low, control and high levels of calcium (2.62%, 3.7% and 4.4%, respectively) for 60 days, using a 3 × 3 factorial arrangement. Compared with the control energy diet, high- and middle-energy diets increased fat deposition and egg weight, decreased feed intake and bone quality and had no effects on eggshell quality. The high-energy diet reduced the serum phosphate concentration and elevated osteocalcin mRNA expression in the keel bone without increasing osteocalcin protein. Dietary calcium intake did not affect fat deposition, feed intake or egg weight. Low dietary calcium resulted in weaker eggshells and poorer bone quality than that from hens fed the control diet. High dietary calcium increased serum calcium concentration, osteoprotegerin mRNA and osteocalcin protein and inhibited serum alkaline phosphatase activity and decreased its mRNA compared with low or control dietary calcium. The high-energy and high-calcium diet significantly reduced egg production. Compared with the control energy diet, high- and middle-energy diets increased fat deposition but had negative effects on bone metabolic homeostasis. Dietary calcium did not influence fat deposition but a high-calcium diet benefited bone homeostasis, while a low-calcium diet was associated with poorer eggshell quality and bone homeostasis.

Interaction of hen production type, age, and temperature on laying pattern and egg quality

The effect of production type (layer vs. broiler breeder), age (onset and end of laying cycle), and temperature (20 and 28°C) on various aspects of the egg production process and quality was evaluated. Highly significant differences were detected between laying hens and broiler breeders (P ≤ 0.001) in all production parameters. Similarly, age significantly affected rate of lay (P ≤ 0.001; 75.4% for young vs. 62.6% for old), mean sequence length (P ≤ 0.001; 7.7 d for young vs. 2.6 d for old), and time of oviposition (P ≤ 0.001). However, there was no effect of temperature on rate of lay, sequence length, or feed intake. Significant interactions between hen type and age were apparent in rate of lay (P ≤ 0.001), sequence length (P ≤ 0.001), and time of oviposition (P ≤ 0.001). A significant interaction between production type and age (P ≤ 0.015) was evident in egg weight, but egg component proportions were dependent only on hen type. Egg shape index was significantly affected by age (P ≤ 0.004), by temperature (P ≤ 0.028), and an interaction between type and age (P ≤ 0.001). Specific gravity declined with age (P ≤ 0.035) and increasing temperature (P ≤ 0.013).

Effect of reduced energy, protein and entire substitution of inorganic phosphorus by phytase on performance and bone mineralisation of laying hens

1. The objective of this study was to evaluate the effects of total removal of dietary inorganic phosphorus and reduced energy and protein, without and with phytase supplementation, on the performance, egg quality and bone composition of laying hens. 2. Lohmann pink-shell hens were randomly assigned at 56 weeks of age to 5 treatments for 20 weeks as follows: (1) a positive control (PC) with 155 g CP/kg, 11·09 MJ ME/kg, calcium (Ca) 3·40% and non-phytic phosphorus (NPP) 0·26%, (2) a negative control (NC1) diet based on PC diet with Ca decreased to 3·30% and NPP to 0·14%, (3) NC2 diet was formulated on the basis of NC1 diet with 152·7 g CP/kg, 10·90 MJ/kg, (4) NC1 and (5) NC2 supplemented with phytase (300 FTU/kg) each. 3. Feed intake, hen-day or hen-housed egg production, egg number per hen-housed, and final body weight were depressed with NC1 and NC2 diets, but restored by phytase inclusion. There were no significant differences between the dietary treatments for feed conversion efficiency, rates of cracked and broken eggs, egg-shell thickness or egg-shell strength. Mortality was significantly increased by NC2 diet without phytase. Tibia ash was significantly decreased by both NC1 and NC2 diets. Bone strength, and Ca and P contents in tibia ash were significantly increased by phytase inclusion in the NC1 diet. 4. In conclusion, the NC1 and NC2 diets significantly depressed performance and tibia quality, but the addition of phytase (300 FTU/kg) significantly improved performance and tibia integrity.

Effects of reduced calcium and phosphorous diets supplemented with phytase on laying performance of hens

The aim of this experiment was to examine the potential for reduced environmental impact by reducing dietary calcium and phosphorus content and phytase addition of laying hen diets. A randomized complete block design with a 2x2x2 factorial arrangement of 8 dietary treatments: 2 levels ofphytase (0 and 300 FTU kg(-1)) and 2 mineral levels (Ca: 34/18 and NPP: 3.2/2.2 g kg(-1), respectively). A total of 240 White Leghorn (WL) layers, 25 weeks of age were used. Considering birds in 12 cages as a replicate, 5 such replicates were randomly allotted to each dietary treatment. Individual body weight of the bird was recorded at the beginning and end of the experiment. Egg production on an individual basis was recorded daily and percentage hen day egg production was calculated. The cleaned eggshells were dried for 24 h, weighed and expressed as percentage of whole egg. One bird from each experimental unit were selected at random and killed by cervical dislocation at the end of the experiment and the left tibia was removed. Dried bone samples were ashed at 680 degrees C for 12 h for estimation of bone ash. The results of this experiment showed that reducing Ca and NPP (Non-Phytate Phosphorus) without phytase decreased BWG (Body Weight Gain), feed intake, FCE (Feed Conversion Efficiency), egg production, egg shell weight and tibia ash. However, phytase addition to low mineral diets completely corrected the adverse effects associated with low dietary Ca and NPP. It can therefore be concluded that reducing levels of Ca and NPP below current standards and phytase supplementation can reduce pollution potential from laying hen production without adversely affecting bird performance or welfare.

Effects of qualitative feed restriction during rearing on the performance of broiler breeders during rearing and lay

To prevent health and fertility problems associated with excessive weight gain, broiler breeders are severely feed restricted during rearing, which may affect welfare. We compared the effects of an experimental ad libitum feeding regimen based on qualitative restriction of food intake with conventional quantitative food restriction on the performance of female broiler breeders during rearing and lay. During rearing up to 20 wk of age, control birds were fed restricted amounts of standard broiler breeder mash once daily. Experimental birds had ad libitum access to the same standard mash mixed with 400 g of oat hulls/kg of feed and increasing concentrations of Ca propionate, an appetite suppressant. Mean total mash intake during rearing was 8.12 kg and did not differ between treatments. Both control and experimental birds showed an almost linear growth curve, treatment mean body weights were always within 100 g of the target weight line, and treatments did not differ for body weight uniformity. Groups were subjected to the same quantitative feed restriction from during lay. Feeding regimen during rearing did not affect number of eggs produced, egg weight, or egg quality up to 46 wk of age. We concluded that it may not be necessary to subject chicks to severe quantitative feed restriction to achieve desirable growth curves and body weight uniformity during rearing. Qualitative restriction of feed intake can achieve desirable growth curves in ad libitum fed chicks during rearing, and such a feeding regimen does not have negative effects on hen performance during lay.

Chick Development in Free‐Living Great Tits Parus major in Relation to Calcium Availability and Egg Composition

Evidence from a number of avian studies suggests that limitation of exogenous calcium (Ca) may reduce egg quality and retard nestling growth. However, it is poorly understood whether reduction in chick growth in Ca-poor areas is due to insufficient intake of dietary Ca or caused by maternal Ca limitation mediated through subtle changes in composition of eggs. In this study, we provide new evidence that Ca availability during egg formation may indeed affect egg composition and influence chick development of the great tit Parus major at early developmental stages. Ca-supplemented birds breeding in base-poor pine forests produced eggs with elevated yolk Ca concentration compared with controls, while no such effect of supplementation was detected in case of eggshell thickness. Nestling tarsus length in the first half of the nestling period was positively influenced by both yolk dry mass and yolk Ca concentration. The effect of supplementary Ca did not persist throughout the nestling period; initial effects of egg components disappeared as nestlings aged. We conclude that apparently normal eggs may harbor poor nutrient and mineral conditions for chick growth. Such subtle changes in composition of eggs can depress chick growth, especially in harsh years.

Biological and Economic Optimum Level of Calcium in White Leghorn Laying Hens

Calcium is important in eggshell formation; inadequate levels in the diet of laying hens may affect shell quality and egg production. An experiment with 250 Leghorn Hy-Line W-98 hens was conducted to evaluate 5 dietary Ca levels (2.96, 3.22, 3.83, 4.31, and 4.82%) in 3 laying periods. The evaluated variables were egg production (EP), egg mass (EM), average daily feed intake (ADFI), feed conversion (FC), and specific gravity (SG). The biological optimum level (BOL) of Ca for maximum egg production and specific gravity, and the economic optimum level (EOL) to maximize profits were calculated. There was no interaction between Ca level and laying period. The results show that the Ca level of the diet (P < 0.05) affected the intake of this nutrient (3.34, 3.68, 4.26, 4.89, and 5.39 g bird/day), ADFI (113, 114, 111, 113, and 111 g bird/day), and SG (1.080, 1.081, 1.082, 1.083, and 1.083). As the hens aged, EP and SG diminished (P < 0.05). BOL for maximum EP and SG were 4.34 and 4.62%, and EOL was 4.38%.

Welfare implications of avian osteoporosis

Cage layer fatigue was first noticed after laying hens began to be housed in cages in the mid-20th century. Hens producing eggs at a high rate were most susceptible to the disease. Early research revealed that cage layer fatigue was associated with osteoporosis and bone brittleness. Severe osteoporosis leads to spontaneous bone fractures commonly in the costochondral junctions of the ribs, the keel, and the thoracic vertebrae. Vertebral fracture may damage the spinal cord and cause paralysis. Osteoporosis appears to be inevitable in highly productive caged laying hens. The condition can be made worse by metabolic deficiency of calcium, phosphorus, or vitamin D. Hens in housing systems that promote physical activity tend to have less osteoporosis and rarely manifest cage layer fatigue. Genetic selection may produce laying hens that are less prone to bone weakness. The welfare implications of osteoporosis stem from pain, debility, and mortality associated with bone fracture. The chicken has well-developed neural and psychological systems specialized to respond to pain associated with trauma and inflammation. Although studies on the chicken have not focused on pain due to bone fracture, physiological and behavioral similarities to other species allow inference that a hen experiences both acute and chronic pain from bone fracture. There is little information on osteoporosis in commercial caged layer flocks, however, evidence suggests that it may be widespread and severe. If true, most caged laying hens suffer osteoporosis-related bone fracture during the first laying cycle. Osteoporosis also makes bone breakage a serious problem during catching and transport of hens prior to slaughter. Estimates of mortality due to osteoporosis in commercial caged layer flocks are few, but range up to a third of total mortality. Many of these deaths would be lingering and attended by emaciation and possibly pain. Osteoporosis-related bone breakage during processing has reduced the marketability of spent caged laying hens, contributing to the need to develop humane on-farm killing methods to support alternative means of spent hen disposition. Overall, the evidence indicates that cage layer osteoporosis is a serious animal welfare problem. A determined effort must be made to make the laying hen no longer susceptible to the harmful effects of excessive bone loss.

The effect of phosphorus, phytase enzyme, and calcium on the performance of layers fed corn-based diets

An experiment employing a factorial arrangement of two levels of Ca, two levels of available P (AP), and three levels of phytase enzyme was carried out with 360 ISA White layers from 18 to 67 wk of age. The Ca levels were maintained at 3.7 and 4.0% throughout the experiment. The AP levels were 0.2 and 0.4% for the high and low treatments until 55 wk of age and were reduced to 0.11 and 0.22% thereafter. Phytase enzyme levels were 0, 250, and 500 phytase units (FTU)/kg of feed. In the period before Week 55, either level of AP was likely adequate for maximum production. However, when lower levels of AP were fed after this time, low AP was associated with reduced BW and egg production, and enzyme supplementation was able to compensate for low AP. In this period, high AP and the highest level of phytase produced negative effects on BW, egg weight, and the feed conversion ratio. The ratio of Ca to AP was important; shell quality was best with high or low levels of both. With high levels of Ca, enzyme supplementation compensated for low levels of AP and overcompensated with a high level of AP. These effects were reduced or absent with low levels of Ca. It is clear from this study that phytase enzyme can compensate for low levels of AP in diets based on corn and soybean meal, but that the optimum level of supplementation depends as well on the Ca level.

Management of Spent Hens

When hens kept for commercial egg production reach the end of their economically viable life span, they are usually transported to a processing plant for conversion into meat products. In this article, we review methods used in Canada and the United States for the catching and removing of these "spent" hens from the layer house and the subsequent loading of them onto vehicles for transport, unloading, and slaughter at the processing plant. We outline welfare concerns associated with these procedures with emphasis on bone fractures. We discuss the move toward on-farm euthanasia in North America and the humaneness of the various techniques under investigation. We conclude with recommendations aimed at increasing bone strength and improving the equipment and handling methods used in the movement and slaughter of spent hens.

The influence of environmental temperature on in vivo limestone solubilization, feed passage rate, and gastrointestinal pH in laying hens

Several studies were conducted to determine whether suppression of in vivo limestone solubilization was partially responsible for the reduction of shell quality under conditions of high environmental temperatures. In Experiment 1, excreta from hyperthermic and thermoneutral hens fed three levels of Ca (3.5, 4.3, and 5.2%) at two cycling environmental temperatures (averaging 28.3 and 26.1 C) were analyzed for percentage in vivo limestone solubilization. Hens in Experiment 2 received diets containing 3.9% Ca at 32.8 and 18.3 C. Rate of feed passage and gastrointestinal pH were also measured in Experiment 2. Experiment 3 evaluated the influence of temperature (22.2 and 30.0 C) and feed consumption on percentage limestone solubilization when Ca intake was held constant. In vivo limestone solubilization was influenced by Ca level in Experiment 1, but not by temperature. Hyperthermic hens solubilized a higher percentage of limestone than thermoneutral hens in Experiment 2, but it was concluded that this was due to a difference in Ca consumption and not due to temperature directly. When Ca intake was held constant in Experiment 3, there was no difference in limestone solubilization at the temperatures tested. Rate of feed passage was 16.6% slower in the hyperthermic hens. Crop, proventriculus, and upper small intestine pH were similar at each temperature, but gizzard pH was significantly lower in the hyperthermic hens. It was concluded that the high environmental temperatures used in the present studies did not suppress in vivo limestone solubilization.