Physiological regulation of calcium and phosphorus utilization in laying hens

Implications of high-dose vitamin D3 with and without vitamin C on bone mineralization and blood biochemical factors in broiler breeder hens and their offspring

As broiler breeder hens age, they often experience a decline in bone mineralization and calcium absorption, especially during the later stages of egg production. This issue not only affects the hens' health, making them more prone to conditions like osteoporosis, but it also impacts the quality of their offspring. To tackle this problem, our study explores whether supplementing these hens with a combination of vitamins D3 and C could help improve their bone health and overall biochemical balance, both for them and their progeny. The goal of this research was to evaluate the effects of high doses of vitamin D3, with and without added vitamin C, on bone mineralization and key blood parameters in aging broiler breeder hens and their offspring. In this experiment, 240 hens and 24 roosters from the Ross 308 strain, aged between 49 and 61 weeks, were used, and a two-way ANOVA (2 × 2) design was applied. This involved two levels of vitamin D3 (3,500 IU and 5,500 IU) and two levels of vitamin C (0 and 150 mg/kg), with six replications of 10 hens and one rooster per group. At the end of the study, blood samples were collected from hens and their offspring for biochemical analysis, and tibia bones were taken for ash content and mineralization assessment. The findings showed that vitamin D3 supplementation significantly lowered blood cholesterol, alkaline phosphatase (ALP), and parathyroid hormone (PTH) levels (P < 0.05), while boosting calcium, 25-hydroxycholecalciferol (25(OH)D3), and 1,25-dihydroxycholecalciferol (1,25(OH)2D3) (P < 0.05). Higher doses of vitamin D3 also improved the strength, resistance, and ash content of the hens' tibia bones, and increased calcium in the carcasses of their offspring. Adding 150 mg/kg of vitamin C to the diet also had a positive effect, reducing cholesterol, ALP, and PTH, while enhancing plasma calcium, total antioxidant capacity, and the active form of vitamin D3 (P < 0.05). Vitamin C supplementation significantly strengthened the tibial bones of the hens and improved plasma calcium and PTH levels in their offspring (P < 0.05). Interestingly, combining elevated doses of both vitamins D3 and C resulted in even greater improvements in tibial bone strength (P < 0.05). In conclusion, giving hens 150 mg of vitamin C along with 5,500 IU of vitamin D3 leads to substantial improvements in the calcium content and structural integrity of their bones, and also boosts calcium and ash content in the carcasses of their offspring.

The Influence of Different Light Day Distribution in Hy-Line W36 Laying Hens on Egg Production and Egg Quality

Laying hens are commonly provided with 16 h of continuous light and 8 h of continuous darkness, with eggshell calcification largely developing during dark hours when dietary calcium is depleted simultaneously with the daily fasting period in laying hens. This phenomenon is thought to be the leading cause of osteoporosis in modern commercial flocks. This trial examined how disrupting the midnight phase affected egg quality in Hy-line W36 hens assigned to control (C) or treatment groups (W1 or W2) from 20 to 70 weeks of age. C hens received 16 h of light and 8 h of dark. W1 hens received 1 h of scotophase interruption, whereas W2 hens received 2 h of scotophase interruption. Across weeks, performance, production, and egg quality measures were measured (p < 0.05). Scotophase interruption displayed a positive effect on the treatment groups in terms of HDEP (week 50: p = 0.028, 0.016; week 70 = 0.031,0.022), damaged eggs (week 50: p = 0.012, 0.021, week 70: p = 0.019, 0.025), eggshell weight (week 30: p = 0.021, 0.027; week 50: p = 0.022, 0.024; week 70; p = 0.018, 0.019), eggshell thickness (week 30: p = 0.017, 0.022; week 50: p = 0.018, 0.031; week 70; p = 0.029, 0.033), ash percent week 30: p = 0.027, 0.021; week 50: p = 0.012, 0.014; week 70; p = 0.031, 0.034), and eggshell strength (week 30: p = 0.025, 0.023; week 50: p = 0.019, 0.021; week 70; p = 0.029, 0.015) in W1 and W2 birds compared to C birds.

Provisioning of vitellogenic follicles continues after green turtles arrive at the nesting beach

Understanding the energetic demands of reproduction on female sea turtles is crucial for devising effective conservation strategies aimed at supporting the reproductive health and resilience of populations at nesting habitats. We studied the ovaries of 69 green turtles (Chelonia mydas) preyed upon by jaguars (Panthera onca) during three nesting seasons at Tortuguero, Costa Rica, the main green turtle Atlantic nesting beach. Our findings revealed a bimodal distribution of vitellogenic follicles, with 'dominant' follicles destined for ovulation and 'non-dominant' follicles to be resorbed. Female green turtles lay, on average, six clutches with ~110 eggs each per nesting season, and a size hierarchy was also found within dominant follicles. During the nesting season, the diameter of small dominant follicles increased by 66% prior to ovulation. Analysis of yolk composition showed that small dominant follicles had higher percent water content than large dominant follicles, which indicates dry matter deposition rather than hydration is responsible for the pre-ovulatory increase in diameter of green turtle dominant follicles during the nesting season. Furthermore, percentages of lipid, nitrogen (N) and phosphorus (P) in the yolk dry matter were constant across green turtle vitellogenic follicles, which underscores that the increase in follicle size results from provisioning with yolk containing similar proportions of these nutrients. Atretic follicles had higher water and lower P percentages than dominant follicles, indicating an accelerated resorption of phosphorus over lipids and N, which could be due to the importance of this nutrient for eggshell production. Finally, >49% of the energy required for egg production was still to be invested during the nesting season, and yolk from non-dominant follicles would not have provided sufficient energy for most females to complete yolk deposition. These insights into follicular dynamics and nutrient provisioning clarify the ongoing reproductive investments made by female green turtles at Tortuguero.

Investigation of Off-Season Breeding Effects on Egg-Laying Performance, Serum Biochemical Parameters, and Reproductive Hormones in Zhedong White

Off-season breeding is a method of encouraging animals through manual intervention to reproduce during the non-breeding season. The egg-laying period of the Zhedong white goose usually starts from September and ends in April of the following year. During the summer months from May to August, with long daylight hours and high temperatures, the white geese rest and do not lay eggs. This study explored the effects of off-season breeding on egg production performance, serum biochemical indicators, and hormone secretion in Zhedong white goose. The experiment was divided into normal breeding and off-seasonal breeding. The results suggested that the peak laying period lasted 3 months, and egg production was 15.62% higher than that in the control group in the off-season breeding group. The off-season breeding group had a 4.13% higher egg fertilization rate in November (laying period) than the control group, and the hatching rate of hatched eggs and fertilized eggs in the peak laying period was 2.77% and 2.3% higher, respectively, than the control group. The experimental group showed significantly higher serum P, ALB (albumin), TG (triglyceride), and TC (total cholesterol) levels; serum AST (glutamic oxalacetic transaminase) activity; and CREA (creatinine) and BUN (blood urea nitrogen) levels than the control group at different time points. The serum LH (luteinizing hormone), FSH (follicle-stimulating hormone), P4 (progesterone), and E2 (estradiol) levels were significantly higher in the off-season breeding group than in the control group. The serum T3 (triiodothyronine) and T4 (Tetraiodothyronine) levels were significantly higher in the off-season breeding group than in the control group at different points in the breeding cycle. The control group showed a significantly higher gene expression of GnRH (gonadotropin releasing hormone) in the hypothalamus; GnRH, FSH, and LH in the pituitary; and GnRH in the ovary and significantly lower gene expression of VIP (vasoactine intestinal peptide) and PRL (prolactin) in the pituitary than the off-season breeding group. Thus, the off-season breeding of Zhedong white geese may prolong the peak laying period and improve egg production performance, thus enhancing the economic benefits of goose breeding.

Effects of a transient lack of dietary mineral phosphorus on renal gene expression and plasma metabolites in two high-yielding laying hen strains

BACKGROUND

There is an emerging body of evidence that current poultry feed is formulated in excess for phosphorus (P), which results in unnecessarily high P excretions. Sustainable concepts for agricultural P flows should trigger animal-intrinsic mechanisms for efficient P utilization. In the current study, Lohmann Brown (LB) and Lohmann Selected Leghorn (LSL) laying hens were fed either a high P diet (P+) with 1 g/kg mineral P supplement or a low P diet (P-) with 0 g/kg mineral P supplement for a period of 4 weeks prior to sampling. Before and after onset of laying, i.e., at 19 and 24 weeks of life, kidney and plasma samples were collected to investigate the endogenous P utilization in response to restricted dietary P, laying hen strain, and sexual maturation.

RESULTS

Plasma analyses of minerals and metabolites confirmed the response to a low P diet, which was characterized by a significant reduction in plasma P levels at week 19 in both strains. The plasma calcium (Ca) levels were tightly regulated throughout the entire experimental period. Notably, there was a numerical trend of increased plasma calcitriol levels in P- fed birds of both strains compared to the P + group, which might have mediated a substantial role regarding the adaptive responses to low P supply. At week 19, RNA sequencing of kidney identified 1,114 and 556 differentially expressed genes (DEGs) unique to the LB and LSL strains, respectively. The number of DEGs declined with increasing maturity of the hens culminating in 90 and 146 DEGs for LB and LSL strains at week 24. Analyses revealed an enrichment of pathways related to energy metabolism and cell cycle, particularly at week 19 in both strains. The diet-specific expression of target genes involved in P homeostasis highlighted transcripts related to active (SLC34A1, SLC20A2) and passive mineral transport (CLDN14, CLDN16), Ca utilization (STC1, CALB1), and acid-base balance (CA2, SLC4A1).

CONCLUSIONS

Results suggest that both laying hen strains adapted to the lack of mineral P supplements and achieved a physiological Ca: P-ratio in body compartments through endogenous regulation as evidenced via the endocrine profile.

Age-related calcium signaling disturbance restricted cAMP metabolism and induced ovarian oxidation stress in laying ducks

The ovary is the main controller of female fertility, unfortunately, its onset of aging processes was earlier than other organs. Our previous studies showed calcium (Ca) deficiency reduced ovarian weight and declined numbers of dominant follicles in an avian model. However, whether Ca provided a functional role in follicle development of aged avian, and its further mechanism was still unknown. In this study, fifty180-day-old and fifty 700-day-old female Longyan ducks were divided into the young group and the aged group to illustrate the differences of Ca signaling and further mechanisms. We found the poor productive performance of aged ducks was correlated with follicle decreased numbers and atrophied microstructure, and restricted antioxidant ability of granulosa cells (GCs). Then, according to RNA-Seq analysis, we detected those aged ducks displayed lower Ca concentration in the ovary, while Ca channel related gene expression was increased in GCs to maintain homeostasis. Moreover, the cyclic adenosine monophosphate (cAMP) concentration and cAMP synthase family related genes were also decreased in GCs of aged ducks. Fortunately, medium supplemented with Ca channel-activator A23187 enhanced GC viability, antioxidant ability, tight junction ability, and increased cAMP concentration by improved cAMP metabolism, otherwise, the opposite changes were observed with Ca2+-chelating agent EGTA or Ca channel-inhibitor Verapamil supplementation. In conclusion, aging disordered Ca signaling to limit cAMP metabolism, then decreased antioxidant ability and inhibited proliferation and migration ability of GCs. Thus, the follicle development and reproductive performance were restricted in aged avian.

Gga-miR-34b-3p targets calbindin 1 to regulate cellular calcium ion homeostasis during eggshell calcification in chicken uterus

Improving eggshell quality in poultry is a key breeding goal, and identifying genetic markers that regulate eggshell calcification is essential for accelerating genetic advancements. This study focused on identifying the keys genes and molecular mechanisms that regulate eggshell calcification in the chicken uterus. The results showed that rapid eggshell mineralization began approximately 4 h after the egg enters the uterus, corresponding with observed morphological and histological changes in the uterine tissue. This is associated with increased energy demands and the production of ion transport proteins. Transcriptome analysis identified calbindin-1 (CALB1), ATPase plasma membrane Ca2+ transporting 2 (ATP2B2), and gga-miR-34b-3p as differentially expressed during eggshell formation. CALB1 and ATP2B2 were predicted targets of gga-miR-34b-3p, with roles in maintaining cellular calcium ion balance. A dual-luciferase reporter assay confirmed that gga-miR-34b-3p directly targeted inhibited CALB1 expression, although no significant changes in the luciferase activity were observed with the co-transfection of ATP2B2 wild-type and gga-miR-34b-3p mimic. Validation experiments showed significant increases in CALB1 and ATP2B2 mRNA and protein levels of CALB1 and ATP2B2 in the chicken uterus during eggshell calcification, with CALB1 predominantly expressed in the cytoplasm of uterine tubular gland cells. Furthermore, primary uterine tubular gland cells, identified using immunofluorescence for Cytokertin 18, demonstrated that silencing CALB1 and ATP2B2 increased intracellular Ca2+ concentration in these cells. Taken together, these findings suggest that the gga-miR-34b-3p/CALB1 regulatory axis maintains calcium ion homeostasis in the uterine tubular gland cells, to facilitate continuous and efficient eggshell calcification and thereby enhancing eggshell quality in chickens.

Quality assessment of spent laying hens and analysis of influencing factors

In China, a considerable number of spent laying hens are disposed annually, with the majority being processed into various food products. The sale of spent laying hens has become a significant revenue stream within the poultry industry. We selected spent laying hens at 100 weeks of age as the research subjects to explore the factors influencing their market price. Information was gathered through product and enterprise investigations. Thereafter, 90 Rhode Island Red laying hens, also at 100 weeks old, were acquired for slaughter. The carcass evaluation was conducted utilizing the methodology prescribed by the United States Department of Agriculture (USDA). Tibial specimens were procured for the purpose of quantifying their length, mass, diameter, maximum breaking strength, maximum breaking distance, as well as for determining the concentrations of calcium, phosphorus, and ash content. Through comprehensive market research and industry surveys, this study found that the primary factor affecting the selling price of spent laying hens is body weight, with 1.5 to 2 kg of chickens being preferred. The USDA quality assessment standards for post-slaughter evaluation, it was found that the incidence of dislocation was 11.1 %, which emerged as a primary factor affecting carcass quality, directly resulting in a decline in quality. The results of the correlation analysis showed that there was no significant relationship between the bone health status and dislocation in laying hens. Dislocations occur mainly due to direct external forces during the culling process caused by the injuries during the slaughter process. Surveys show that the main factor affecting the selling price of spent laying hens is body weight, and the optimal weight range is where farmers gain price advantages during the culling process. The principal factor impacting the carcass quality of spent laying hens is dislocation, which are mainly caused by excessive culling and have no obvious correlation with bone health.

Effects of feeding diets without mineral P supplement on intestinal phytate degradation, blood concentrations of Ca and P, and excretion of Ca and P in two laying hen strains before and after onset of laying activity

The objective of this study was to characterize intestinal phytate degradation and mineral utilization by 2 laying hen strains before and after the onset of egg laying using diets without or with a mineral phosphorus (P) supplement. One offspring of 10 roosters per strain (Lohmann Brown-classic [LB] and Lohmann LSL-classic [LSL]) was sacrificed before (wk 19) and after (wk 24) the onset of egg-laying activity and following 4 wk placement in a metabolic unit. Diets were corn-soybean meal-based and without supplemented P (P-) or with 1 g/kg supplemented P (P+) from monocalcium phosphate. In wk 19 and 24, the blood plasma and digesta of duodenum+jejunum and distal ileum were collected. The concentration of P in blood plasma was higher in hens fed P+ than P- (P < 0.001). In duodenum + jejunum and ileum content, the concentrations of InsP6, Ins(1,2,4,5,6)P5 and Ins(1,2,3,4,5)P5 were lower in P- than in P+ (P ≤ 0.009). In duodenum+jejunum, the concentrations of InsP6, Ins(1,2,4,5,6)P5 and Ins(1,2,3,4,5)P5 were lower in wk 24 than 19 and lower in LSL than LB hens (P < 0.001). The concentration of myo-inositol (MI) in duodenum + jejunum content was lower in wk 19 than 24 (P < 0.001). Following a 4-d total excreta collection, the retained amount of P was higher in P+ than P- (P < 0.001). Phosphorus retention was lower in LB hens fed P- than in other treatments (P × strain: P = 0.039). In the jejunal tissue, some genes related to intracellular InsP metabolism were higher expressed in LB than LSL hens. The renunciation of mineral P increased endogenous phytate degradation, but more P was retained with supplemented P. Differences in endogenous phytate degradation between the periods before and after the onset of egg laying might be attributed to different Ca concentrations in intestinal digesta caused by different Ca needs in both periods.

Comparative analysis of reproductive hormones, serum biochemical indexes and ovarian metabolites in Muscovy breeder duck at different laying stages

The hypothalamic-pituitary-gonadal (HPG) axis regulates egg laying through control hormones secretion in poultry. In this study, the serum hormones (12 samples per stage), serum biochemical indexes (12 samples per stage), and ovarian metabolites (8 samples per stage) of Muscovy breeder ducks were detected at prelaying stage (PT), start of laying stage (ST), high laying stage (HT), and the end of laying stage (ET). The serum hormones of Muscovy ducks were measured at 8:00, 13:00, 18:00, 23:00, and 4:00 within 1 d. The TG, TP, ALB, and GLB were significantly increased, while HDL-C was significantly decreased at ST as compared to PT (P < 0.05). Serum Na, Cl, Ca, P, and K showed significant rise at ST as compared to PT. Serum Na, Cl, Ca, and K were significantly declined, while P was significantly increased at ET as compared to HT (P < 0.05). Serum FSH, LH, PRL, E2, P4 levels peaked at ST (P < 0.05) with only FSH and LH fluctuated significantly within 1 ovulation cycle at ST (P < 0.05). Differential metabolites showed continued ovarian aging. The decline of nucleic acid metabolism occured in ST, the decline of sugar metabolism occurred in ET, and the decline of amino acid metabolism continued at all stages. Temporal expression patterns and correlation analyses indicated a high correlation between ovarian cAMP and serum reproductive hormone levels across different reproductive stages. In conclusion, this study revealed the changes in serum hormones, serum biochemical indicators, and ovarian metabolites, as well as the relationship between serum hormones and ovarian metabolites.

Dietary supplementation with 25-hydroxyvitamin D3 regulates productive performance, lipid metabolism and gut microbiota in aged laying ducks

The aim of this study was to investigate the effect of dietary supplementation with 25-hydroxyvitamin D3 (25(OH)D3) on productive performance, lipid metabolism and gut microbiota in aged laying ducks. A total of 432 healthy Longyan ducks at 60-week of age were randomly allotted to 6 groups, each with 6 replicates of 12 ducks. Ducks were given a basal diet (without added 25(OH)D3) or that diet supplemented with 800, 1600, 2400, 3200, or 4000 IU/kg 25(OH)D3 for a total of 16 wk. Dietary supplementation with 25(OH)D3 improved egg production, egg mass and average daily feed intake, and decreased the feed conversion ratio (FCR) of ducks during the whole trial period (linear, quadratic; P < 0.05). Supplementation with 25(OH)D3 decreased very low-density lipoprotein (VLDL) content in yolk (P = 0.008), decreased high-density lipoprotein and low-density lipoprotein (LDL) content in plasma (P = 0.002). Hepatic index, VLDL, LDL, triglyceride and total cholesterol content in liver, nonalcoholic fatty liver activity score of liver and alanine aminotransferase activity in plasma were decreased with supplementation of 25(OH)D3 (linear or quadratic; P < 0.05). The decreased hepatic apolipoprotein B 100 and lipoprotein lipase expression, and increased hepatic peroxisome proliferator-activated receptor-α and sterol regulatory element binding protein-1 expression resulted from 25(OH)D3 supplementation (linear, quadratic; P < 0.05). Moreover, 25(OH)D3 supplementation increased the villus/crypt ratio (linear, quadratic; P < 0.05) and expression of zonula occludens protein 1 and nuclear factor-κ-gene binding in duodenum (P < 0.05). The supplementation of 25(OH)D3 reduced the abundance of Wittenberg polluted soil-2 bacteria, Synergistota, Bacteroidales, Colidextribacter, Eggerthellaceae, Oscillospira, Oscillibacter, UCG-009, Barnesiellaceae and Lachnospiraceae_UCG-010 in cecal contents (P < 0.05). Dietary requirements for 25(OH)D3 for ducks (60 to 76 wk), were estimated to be 3377 IU/kg for egg production, 3434 IU/kg for egg mass, and 3256 IU/kg for FCR. In summary, dietary 25(OH)D3 supplementation improved productive performance and influenced liver and plasma lipid homeostasis in aged laying ducks, which may be associated with the reduction of bacteria involved in carbohydrate metabolism in the cecum. Supplementing the basal diet with 3250 to 3450 IU/kg 25(OH)D3 is recommended for aged laying ducks (60 to 76 wk).

Rearing laying hens: Early environmental complexity and genetic strain have life-long effects on keel bone size and fractures

Keel bone damage (KBD) is a major welfare concern for laying hens. Environmental complexity during rearing is suggested to promote skeletal development and reduce KB fractures (KBF). We investigated the effect of rearing environment and genetic strain on KB development and health. Three consecutive replicate flocks of brown (B) and white-feathered (W) layer chicks (3000/ flock) were raised in three styles of rearing aviaries of Low,Mid, or High complexity and in conventional cages (Conv). Pullets from flocks 1 and 3 (1080/ flock) were subsequently housed in 24 furnished cages of two sizes (small: 30 vs large: 60 birds) for lay. Samples of pullets and hens were assessed as follows: Dissections at six, 11, and 16 WoA in flocks 1 and 2 for KB size, radiographs at 30, 50, and 70 WoA in flocks 1 and 3, for KBD and dissections at 70 WoA in flock 3 for KBD. Rearing complexity affected KB size of pullets (Conv < High < Mid, Low; P< 0.0001). W pullets had larger keels than B when adjusted for body weight throughout rearing (strain x age P= 0.005) and at 70 WoA (P< 0.001). KBF prevalence at end-of-lay was affected by rearing complexity (High < Low, Conv, P= 0.002). During lay, KBF severity was affected by rearing complexity (High < Low, Mid; P= 0.007), strain (W < B; P< 0.0001) and age (30 < 50 < 70 WoA; P< 0.0001). At 70 WoA, an interaction of rearing by strain affected KBF severity (most severe: B-Conv, least severe: B-Mid and W-High, P= 0.003). KBF severity scores from radiographs and dissections corresponded moderately (r= 0.547, P< 0.0001). The severity of KB deviations was affected by the size of the furnished cages (large > small, P= 0.049). In conclusion, rearing complexity and strain affected KB size and fracture severity and prevalence. These data confirm that complex rearing aviaries that are known to promote exercise reduce KBF severity and prevalence throughout lay.

Effects of dietary free fatty acid content and degree of fat saturation on tibia bone properties of laying hens

Acid oils and fatty acid distillates are fat by-products of the refining process of edible oils and are characterized by their high proportion of free fatty acids (FFA). While lipids are essential in poultry diets, their chemical structure may interfere with calcium absorption. Therefore, this study investigated the effects of dietary FFA content and the degree of fat saturation on bone metabolism in commercial layers. For 15-wk, a total of 144 laying hens (19-wk-old) were randomly assigned to 8 treatments (6 replicates with 3 birds each), which were obtained by gradually replacing crude soybean oil (rich in unsaturated fatty acids [UFA]) with soybean acid oil (rich in UFA and FFA), or crude palm oil (rich in saturated fatty acids [SFA]) with palm fatty acid distillate (rich in SFA and FFA). Following a 2 × 4 factorial design, 4 UFA-rich and 4 SFA-rich diets were created with varying FFA content: 10, 20, 30, and 45%. Tibiae (6 birds/treatment) were collected at the end of the trial for the assessment of mineral composition, morphological properties, and mechanical characteristics. The data were analyzed using a 2-way ANOVA with the GLM procedure. Orthogonal polynomial contrasts were employed to determine the linear effect of increasing %FFA, with statistical significance set at P < 0.05. The degree of saturation was found to negatively impact on calcium and phosphorus bone content, with higher levels found in soybean-based diets (P < 0.001). A significant interaction was observed for medullary bone mineral content, showing a linear decrease as the dietary %FFA increased (P < 0.05) in palm diets. In contrast, morphological and mechanical bone traits, total ash content, and cortical bone mineral composition remained unaffected (P > 0.05). These results suggest that the degree of fat saturation exerts a greater impact than FFA content on bone mineral metabolism, supporting the commercial use of fat by-products rich in FFA in laying hen diets, at least during the early stages of the laying cycle.

Evaluating the effect of optimal zinc amino-acid complex supplementation in laying pullets on performance and zinc retention

This study investigated the optimal dietary intake of zinc amino acid complex (Zn-AAC) for white-layer pullets, focusing on their productive performance, biochemical profile, organ biometry, and body zinc retention. The study involved 360 Dekalb White pullets (average weight: 433 ± 4.42 g) aged from 6 to 16 weeks and distributed into 6 treatments with 6 replications each. The Zn-AAC inclusion levels ranged from 5 to 75 mg kg-1. Zinc intake was modeled using a nonlinear equation, Y = ∝ *1- e-βX, where α is the maximum response, β is the rate at which the response approaches the maximum (P < 0.05). The Zn-AAC supplementation had significant effects on average daily gain (ADG), average daily feed intake (ADFI), and feed convention ratio (FCR) (P < 0.01). Optimal intake levels of Zn-AAC were estimated at 0.234, 0.340, and 0.315 mg bird-1 day-1 (5.42, 7.87, and 7.30 mg kg-1) for ADG, ADFI, and FCR, respectively. The Zn-AAC supplementation affected the Zn body retention in pullets (P < 0.01), with an optimal ingestion at 1.86 mg bird -1 day-1, corresponding to a dietary supplementation of 43.10 mg kg-1. Additionally, supplementation affected alkaline phosphatase (ALP) activity (P < 0.01) without significant changes in aspartate aminotransferase, albumin, and globulin levels. The optimal Zn-AAC intake level for ALP activity was 1.45 mg bird -1 day-1, corresponding to dietary supplementation of 33.60 mg kg-1. Based on Zn body retention, we recommend up to 1.86 mg bird -1 day-1 of Zn-AAC, which is equivalent to 43.10 mg kg-1.

Review: Welfare in farm animals from an animal-centred point of view

This review aimed to enlighten aspects of welfare from the farm animal-centred point of view rarely addressed such as those anatomical and physiological alterations induced in farm animals to obtain high performance. Hence, the major working hypothesis was that high-producing farm animals developed an imbalance between body structural and functional capacities and the genetic procedures applied to obtain industrial production of animal protein. This is called "disproportionality", a feature which cannot be compensated by feeding and management approaches. Consequences of disproportionality are the insidious development of disturbances of the metabolism, low-grade systemic inflammation and as a final stage, production diseases, developing throughout the productive life span of a farm animal and affecting animal welfare. Based on scientific evidence from literature, the review discusses disproportional conditions in broilers, laying hens, sows, piglets, dairy cows, bulls and calves as the most important farm animals for production of milk, meat, foetuses and eggs. As a conclusion, farm animal welfare must consider analysing issues from an animal-centered point of view because it seems evident that, due to genetics and management pressures, most of farm animals are already beyond their physiological limitations. Animal welfare from an animal-centered point must be addressed as an ethical step to establish limits to the strength placed on the animal's anatomical and physiological functionality. It may allow more sustainable and efficient farm animal production and the availability of healthy animal-derived protein for human nutrition worldwide.

Physiological changes in the regulation of calcium and phosphorus utilization that occur after the onset of egg production in commercial laying hens

At the onset of egg production, physiological changes governing calcium and phosphorus utilization must occur to meet demands for medullary bone formation and eggshell mineralization. The objective of this study was to identify these changes and determine if they are influenced by dietary supplementation with 1α-hydroxycholecalciferol (AlphaD3™, Iluma Alliance). Commercial laying hens fed either a control or AlphaD3-supplemented diet beginning at 18 weeks of age were sampled at 18 (n = 8) and 31 weeks (n = 8/diet) to evaluate mRNA expression associated with calcium and phosphorus utilization in kidney, shell gland, ileum, and liver, circulating vitamin D3 metabolites, and bone quality parameters in humerus, tibia, and keel bone. Though diet did not heavily influence gene expression at 31 weeks, several significant differences were observed between 18- and 31-week-old hens. Heightened sensitivity to hormones regulating calcium and phosphorus homeostasis was observed at 31 weeks, indicated by increased parathyroid hormone receptor 1, calcium-sensing receptor, calcitonin receptor, and fibroblast growth factor 23 receptors in several tissues. Increased renal expression of 25-hydroxylase and vitamin D binding protein ( DBP ) at 31 weeks suggests kidney participates in local vitamin D3 25-hydroxylation and DBP synthesis after egg production begins. Biologically active 1,25(OH)2D3 was higher at 31 weeks, with correspondingly lower inactive 24,25(OH)2D3. Increased expression of plasma membrane calcium ATPase 1 and calbindin in kidney, shell gland, and ileum suggests these are key facilitators of calcium uptake. Elevated renal inorganic phosphorus transporter 1 and 2 and sodium-dependent phosphate transporter IIa at 31 weeks suggests increased phosphorus excretion following hyperphosphatemia due to bone breakdown for eggshell formation. Diet did influence bone quality parameters. Bone mineral density in both humerus and tibia was higher in AlphaD3-supplemented hens at 31 weeks. Tibial bone mineral content increased between 18 and 31 weeks, with AlphaD3-supplemented hens increasing more than control hens. Moreover, control hens exhibited diminished tibial breaking strength at 31 weeks compared to hens at 18 weeks, while AlphaD3-supplemented hens did not. Together, these results indicate supplementation with AlphaD3 enhanced bone mineralization during the medullary bone formation period and elucidate the adaptive pathways regulating calcium and phosphorus utilization after the onset of lay.

The relationship between phosphorus retention and fibroblast growth factor 23 in broiler breeders

Previous studies with broiler breeders indicate a P retention threshold when fed daily dietary levels of non-phytate P (NPP) exceeding 320 mg. Fibroblast growth factor 23 (FGF23) is a hormone secreted by osteocytes which modulates P retention and could be the biological agent which controls the P threshold in breeders. To evaluate the relationship between FGF23 and the P retention threshold, a 4-wk study with 32-wk-old breeders was conducted with 6 dietary treatments with daily NPP intake of 216 to 576 mg/d/h with increments of 80 mg/kg diet. The goals were 1) to elucidate how plasma FGF23 corresponds with the P retention threshold in broiler breeders and 2) to determine the amount of P for optimal egg production and bone health. Results showed that between daily 288 mg and 360 mg dietary NPP intake, P retention decreased from 33 to 26% but FGF23 levels increased from 130 pg/mL to 220 pg/mL with increasing NPP. The elevation of plasma FGF23 between the range of 288 mg to 360 mg dietary NPP/d intake suggests that FGF23 is related to the P retention threshold and may be the major hormone for regulating physiological P levels when intake of daily dietary P levels are increased above 288 mg NPP.

Impact of the arginine silicate inositol complex on bone metabolism in broiler chickens with tibial dyschondroplasia caused by manganese deficiency

1. Tibial dyschondroplasia (TD) is a skeletal disorder in broilers that has financial implications, necessitating dietary modifications to reduce the prevalence of this disease. This study explored how arginine silicate inositol complex (ASI) supplementation affected tibial growth plate (TGP) and overall bone health in broilers with manganese (Mn) deficiency-induced TD.2. A total of 240 broiler chicks were divided into four groups, each consisting of 60 birds (15 replicates of four broilers each) as follows: i) Control, with 60 mg Mn per kg of diet; ii) ASI, with 60 mg Mn and 1 g ASI per kg of diet; iii) TD, with 22 mg Mn per kg of diet, and iv) TD+ASI, with 22 mg Mn and 1 g ASI per kg of diet.3. It was found that ASI supplementation increased tibial bone length in Mn-deficient TD broilers (p = 0.007). There was no Mn x ASI interaction for other bone morphometry variables (p > 0.05). However, both tibial bone mineral content and density were affected by Mn and ASI (p < 0.05). With ASI supplementation, serum bone-specific alkaline phosphatase and osteocalcin levels were elevated in the TD+ASI group compared to the TD group (p < 0.001). In the TD group, osteoprotegerin (OPG) levels in the TGP decreased compared to the control groups (p < 0.001).4. In contrast, ASI supplementation in the TD broilers counteracted the decrease in OPG compared to TD broilers without ASI supplementation (p < 0.001). The Mn level and ASI supplementation significantly influenced the OPG/receptor activator of the nuclear factor-κB ligand ratio (p < 0.001).5. In conclusion, the results demonstrated that inclusion of ASI in broiler diets could enhance bone formation variables by controlling OPG levels in the TGP, potentially serving as an effective method to decrease the occurrence of TD.

Utilizing 3-dimensional models to assess keel bone damage in laying hens throughout the lay cycle

The global egg industry is rapidly transitioning to cage-free egg production from conventional cages. Hens housed in cage-free systems have an increased prevalence of keel damage that could lead to reduced egg production and compromised well-being. The objective of this study was to determine the effects of dietary supplementation of n-3 fatty acids and vitamin D3 on keel damage in hens housed in multi-tier aviary systems (AV). Brown hens were placed in 4 AV system rooms after rearing at 17 wk of age (woa) with each room containing 576 birds. At 12 woa, rooms were randomly assigned to a dietary treatment of flaxseed oil, fish oil, vitamin D3, or control. Focal birds (36 per treatment) were longitudinally examined for keel damage using quantitative computed tomography (QCT) at nine timepoints from 16 to 52 woa. Three-dimensional digital twins of the keels were created from the QCT scans and visually assessed for damage. An overall keel severity score was recorded as well as the location, direction, and severity of each deviation or fracture. Severity was ranked on a 0 to 5 scale with 0 being no damage and 5 being severe. Damage scores were analyzed utilizing odds ratios with main effects of age and treatment. At 16 woa, 80% of hens had overall keel scores of 0 and 20% had scores of 1. At 52 woa, all hens had damage, with 31% having a score of 1, 61% scored 2 to 3, and 8% scored 4 to 5. Most fractures were not observed until peak lay. Dietary treatments did not affect likelihood of fracture incidences, but younger birds had lower odds of incurring keel fractures than older birds (P < 0.0001). The initial incidences of keel deviations occurred earlier than fractures, with most birds obtaining a keel deviation by 28 woa. Keel damage was not able to be prevented, but the age at which keel fractures and deviations initiate appear to be different, with deviations occurring during growth and fractures during lay.

Dietary Super-Doses of Cholecalciferol Fed to Aged Laying Hens Illustrates Limitation of 24,25-Dihydroxycholecalciferol Conversion

Background

Older humans taking high concentrations of vitamin D3 supplementation for a prolonged time may be at risk of vitamin D toxicity. It is unclear how dietary super-doses (10,000 times greater than the requirement) can affect vitamin D3 status in aged animals. Aged laying hens could be a model to compare vitamin D3 supplementation effects with women in peri- or postmenopausal stages of life.

Objectives

We investigated the dietary super-dose impacts of cholecalciferol (vitamin D3) on vitamin D3 status in aged laying hens in production.

Methods

Forty-eight 68-wk-old Hy-Line Brown laying hens were individually housed in cages with 8 hens per dietary treatment for 11 wk. Hens were randomly assigned to 1 of 6 treatment groups of dietary vitamin D3 supplementation and consumed ad libitum. Supplementation concentrations were 400, 800, 7400, 14,000, 20,000, and 36,000 IU D3/kg of feed. At the end of the study, all hens were sacrificed, and tissue samples and feces were collected. Plasma and egg yolk vitamin D3 metabolites, calcium and phosphorus composition of eggshells, ileal digesta, and feces were measured. Duodenal, ileal, liver, and kidney gene expression levels were also measured.

Results

We observed that increasing dietary vitamin D3 increased plasma vitamin D3 and egg yolk vitamin D3 (P < 0.0001 for both sites). We also observed an increase in plasma 24,25-dihydroxycholecalciferol as dietary vitamin D3 concentrations increased (P < 0.0001). The plasma 25-hydroxycholecalciferol:24,25-dihydroxycholecalciferol ratio exhibited an asymptotic relationship starting at the 14,000 IU/kg D3 treatment.

Conclusions

Dietary super-doses of vitamin D3 led to greater plasma and egg yolk vitamin D3 concentrations, which shows that aged laying hens can deposit excess vitamin D3 in egg yolk. We suggest future research should explore how 24-hydroxylation mechanisms are affected by vitamin D3 supplementation. Further understanding of 24-hydroxylation can help ascertain ways to reduce the risk of vitamin D toxicity.

Circadian regulation of calcium and phosphorus homeostasis during the oviposition cycle in laying hens

Maintenance of calcium and phosphorus homeostasis in laying hens is crucial for preservation of skeletal integrity and eggshell quality, though physiological regulation of these systems is incompletely defined. To investigate changes in mineral and vitamin D3 homeostasis during the 24-h egg formation cycle, 32-wk-old commercial laying hens were sampled at 1, 3, 4, 6, 7, 8, 12, 15, 18, 21, 23, and 24 h post-oviposition (HPOP; n ≥ 4). Ovum location and egg calcification stage were recorded, and blood chemistry, plasma vitamin D3 metabolites, circulating parathyroid hormone (PTH), and expression of genes mediating uptake and utilization of calcium and phosphorus were evaluated. Elevated levels of renal 25-hydroxylase from 12 to 23 HPOP suggest this tissue might play a role in vitamin D3 25-hydroxylation during eggshell calcification. In shell gland, retinoid-x-receptor gamma upregulation between 6 and 8 HPOP followed by subsequently increased vitamin D receptor indicate that vitamin D3 signaling is important for eggshell calcification. Increased expression of PTH, calcitonin, and fibroblast growth factor 23 (FGF23) receptors in the shell gland between 18 and 24 HPOP suggest elevated sensitivity to these hormones toward the end of eggshell calcification. Shell gland sodium-calcium exchanger 1 was upregulated between 4 and 7 HPOP and plasma membrane calcium ATPase 1 increased throughout eggshell calcification, suggesting the primary calcium transporter may differ according to eggshell calcification stage. Expression in shell gland further indicated that bicarbonate synthesis precedes transport, where genes peaked at 6 to 7 and 12 to 18 HPOP, respectively. Inorganic phosphorus transporter 1 (PiT-1) expression peaked in kidney between 12 and 15 HPOP, likely to excrete excess circulating phosphorus, and in shell gland between 18 and 21 HPOP. Upregulation of FGF23 receptors and PiT-1 during late eggshell calcification suggest shell gland phosphorus uptake is important at this time. Together, these findings identified potentially novel hormonal pathways involved in calcium and phosphorus homeostasis along with associated circadian patterns in gene expression that can be used to devise strategies aimed at improving eggshell and skeletal strength in laying hens.

Shape and fractures of carina sterni in chicken genotypes with different egg deposition rates reared indoor or free-range

Commercial laying hens have high frequency of damage to the keel bone (KB), which causes negative effects on health and welfare. KB damage may consist in fractures (KBF) and deviations (KBD). The aim of the present study was to compare the KB shape, by means of Geometric Morphometric, and the occurrence of fractures in different chicken genotypes reared either free-range (FR) or in enriched cages. Moreover, the relationship between KB shape, genotype and rearing system was analysed. Sixty birds/genotype (2 Italian local breeds, Bionda Piemontese and Robusta Maculata, their crossbreeds with Sasso and Lohmann Brown) were used. All the hens fed the same commercial feed throughout the trial. Body weight, egg production, feed intake and mortality were recorded from 25 to 66 weeks of age. Ca intake (IN) and output (OUT) were estimated and Ca OUT/IN was calculated. FR affected the occurrence of KB deviations but not the shape, whereas the fractures were mainly affected by genotype. Local breeds had a lower prevalence of KBF with similar level of KBD but with different shapes. Crossbreeds seemed to be a suitable compromise between egg deposition rate and occurrence of KB damages.

n-3 essential fatty acid and vitamin D supplementation improve skeletal health in laying hens

Keel bone fractures and osteoporosis are prevalent and damaging skeletal issues in the laying hen industry. There is a large interest in improving bone quality parameters to reduce or eliminate these conditions, thus improving bird welfare. Both essential fatty acids (EFA) and vitamin D can play a role in bone metabolism. The hypothesis of this study was that birds supplemented with lower n-6:n-3 EFA ratio or vitamin D would have improved bone properties compared to a control diet. A total of 3,520 Lohmann Brown-Lite pullets were used in this study. Pullets were housed on the floor from 0 to 17 wk of age and then moved to an aviary (17-52 wk of age). Starting at 12 wk of age, birds were split into diet treatments-control, flax, fish, or vitamin D diets with n-6:n-3 ratios of 6.750, 0.534, 0.534, and 6.750, respectively. Diets were formulated to be isonitrogenous and isocaloric. Basal vitamin D3 levels were formulated to be 2,760 IU/kg across all diets; for the vitamin D diet, the vitamin D3 level was increased to 5,520 IU/kg. Hens on fish and vitamin D diets had greater bone density, keel bone volume, digital bone mineral content, and keel condition compared to flax and control hens. Additionally, birds fed the vitamin D diet had the heaviest body weights compared to birds fed fish or control diets. Birds fed the flax and vitamin D diets had improved feather coverage across multiple body regions. Feeding an n-3 EFA- or vitamin D-enriched diet decreased mortality by 1.6 to 3.3% compared to the control. The fish and vitamin D diets generated mixed production performance. Compared to the other treatments, the vitamin D diet generated higher case weights but lower hen day percentage throughout the study. When compared to the other treatments, the fish diet had the lowest case weights but had a greater hen day percentage after 36 wk of age. Results indicate that a fish-based EFA and vitamin D supplementation show promise in improving skeletal health but require further investigation.

A Novel Bacterial 6-Phytase Improves Productive Performance, Precaecal Digestibility of Phosphorus, and Bone Mineralization in Laying Hens Fed a Corn-Soybean Meal Diet Low in Calcium and Available Phosphorus

Exogenous phytases are commonly added to low-phosphorus and low-calcium diets to improve P availability and reduce P excretion by poultry. This study investigated the effect of supplementation with a novel bacterial 6-phytase on egg production, egg quality, bone mineralization, and precaecal digestibility of P in laying hens fed corn-soybean meal-based diets. A total of 576 Hy-Line brown laying hens were used in a completely randomized block design at 25-45 weeks of age (woa). The three treatments included a positive control (PC) adequate-nutrient diet with 2840 kcal metabolizable energy/kg, 0.77% digestible lysine, 3.5% Ca, and 0.30% available P (avP); a negative control (NC) diet with 0.16% points less Ca and avP; and an NC diet supplemented with a novel bacterial 6-phytase at 300 phytase units/kg diet. Hen performance and the percentage of damaged eggs were measured every 4 weeks. Body weight, precaecal digestibility of P, and bone parameters at 45 woa were also measured. The reduction in avP and Ca in the NC diet did not compromise performance or egg quality. However, it decreased (P < 0.001) body weight, tibial dry matter, tibial ash and P content, and precaecal digestibility of P. Importantly, all these parameters were significantly improved (P < 0.001) and essentially restored to the levels measured in PC diet-fed hens upon supplementation with phytase. In summary, the present study demonstrates that the new bacterial 6-phytase could effectively counteract the negative effects of P and Ca deficiencies on body weight, bone mineralization, and P availability, thereby supporting high productivity without compromising the welfare of laying hens.