Effects of Ovulatory and Egg Laying Cycle on Bone Mineral Density and Content of Live White Leghorns as Assessed by Dual-Energy X-Ray Absorptiometry

Dual-energy X-ray absorptiometry: an effective approach for predicting broiler chicken body composition

Two trials were carried out to develop and validate linear regression equations for body composition prediction using Dual-energy X-ray absorptiometry (DEXA). In Trial 1, 300 Cobb500 male chickens raised from 1 to 42 d of age were scanned in DEXA to estimate total weight, fat mass, soft lean tissue (SLT) mass, bone mineral content (BMC), and fat percentage. DEXA estimates were compared to body ash, crude fat, SLT (sum of protein and water) and scale body weight. The dataset was split, with 70% used for prediction equations development and 30% for testing, and the 5k-fold cross-validation analysis was used to optimize the equations. The R2, mean absolute error (MAE), and root-mean-squared error (RMSE) were used as precision and accuracy indicators. A negative correlation (ρ = -0.27) was observed for ash content, while no correlation was observed for protein content (P > 0.05). Predictive linear equations were developed to assess broiler weight (R2 = 0.999, MAE = 25.12, RMSE = 38.99), fat mass (R2 = 0.981, MAE = 13.87, RMSE = 21.28), ash mass (R2 = 0.956, MAE = 3.98, RMSE = 5.61), SLT mass (R2 = 0.997, MAE = 35.73, RMSE = 52.45), water mass (R2 = 0.997, MAE = 29.56, RMSE = 43.94), protein mass (R2 = 0.989, MAE = 12.94, RMSE = 19.05), fat content (R2 = 0.855, MAE = 0.81, RMSE = 1.05), SLT content (R2 = 0.658, MAE = 1.01, RMSE = 1.28), and water content (R2 = 0.678, MAE = 0.99, RMSE = 1.27). All equations passed the test. In Trial 2, 395 Cobb500 male chickens were raised from 1 to 42 d of age and used for validation of prediction equations. The equations developed for weight, fat mass, ash mass, SLT mass, water mass, and protein mass were validated. In conclusion, DEXA was found to be an effective approach for measuring the body composition of broilers when using predictive equations validated in this study for estimate calibration.

Use of Maca Powder (Lepidium meyenii) as Feed Additive in Diets of Laying Quails at Different Ages: Its Effect on Performance, Eggshell Quality, Serum, Ileum, and Bone Properties

Using additives can reduce the negative effects of aging on factors affecting profitability, such as the availability of nutrients, production, and egg quality. Maca is an herbaceous plant rich in protein, crude oil, essential acids, and pharmacological compounds. Maca has positive effects on different health parameters. In this study, the effect of adding Maca powder to the diets of young and old laying quails at the end of the 10-week trial was investigated. In total, 150 laying Japanese quails (Coturnix japonica) (209.1 ± 10.0 g) were randomly distributed to a 2 × 3 factorial arrangement with two ages (10 weeks and 30 weeks) and three Maca powder levels (0, 1, or 2 g/kg), with five subgroups per treatment. According to the study, eggshell quality, total cholesterol, triglyceride, progesterone, and testosterone concentrations of serum were lower in old quail than in young quail, while egg weight, feed intake, and follicle-stimulating hormone increased significantly as quail aged. (p < 0.05). Furthermore, aging negatively affected the histomorphology of the ileum and cortical bone thickness (p < 0.05). Additional findings show that adding 1 g/kg Maca powder to the diet of quail significantly improved eggshell, ileum, and bone traits that deteriorate with age, without affecting performance, and adding 2 g/kg Maca powder to the diet significantly reduced serum total cholesterol levels (p < 0.05). Incorporating Maca powder into the diet of aged birds could reduce the negative effects of aging.

Correlation and path analysis of assessment methodologies of bone quality from brown egg layers at final of the production cycle

This study aimed to investigate direct and indirect correlations of methodologies of bone quality analysis from brown egg layers, at final of the production cycle. Twelve femurs of Dekalb Brown laying hens, euthanized at 85-week-old, were assessed to evaluate breaking strength (BS), Seedor index (SI), mineral matter (MM), calcium (Ca) and phosphorus (P) contents, besides cortical (CorD), medullar (MedD) and epiphysis (EpiD) diameters. Correlations and path analysis were obtained with the aid of SAS® University (p ≤ 0.05). The BS directly represented the bone quality and was compared to other methodologies. Greater linear correlations occurred between BS and MM (r = 0.82), MM and Ca (r = 0.72), and BS and Ca (r = 0.70). The MM content displayed the greatest direct effect on the BS (r = 0.53). The Ca content showed a reduced direct effect on the BS (r = 0.18), with indirect effects through MM content (r = 0.44) and EpiD (r = 0.15), however, presented a great total correlation (r = 0.78). Determination of mineral matter content is the main methodology associated with femur breaking strength from brown egg layers at final of the productive cycle. Because of that, this methodology is more reliable to determine bone quality.

Effect of Age on Bone Structure Parameters in Laying Hens

Changes in medullary and cortical bone structure with age remain unclear. Twenty Hy-Line W36 hens, 25 or 52 weeks of age, were euthanized, and both tibiae were collected when an egg was present in the magnum. Serial cross sections of the tibiae were stained with Alcian blue. The bones were scanned using micro-computed tomography. Trabecular width (Tb.Wi) was significantly higher (p < 0.05) in 25-week-old hens, whereas medullary bone tissue volume (TV) was significantly higher (p < 0.01) in 52-week-old hens. 25-week-old hens had significantly higher (p < 0.01) bone volume fraction (BVF = calcified tissue / TV). Moreover, the cortical bone parameters were significantly higher (TV and bone mineral content (BMC) at p < 0.05, and bone volume (BV) and BVF at p < 0.01) in younger hens. Open porosity and total porosity, which indicate less density, were significantly higher (p < 0.01) in older hens. Older hens showed significantly higher (p < 0.01) tibial diaphysis TV than younger hens. Younger hens had significantly higher (p < 0.01) BV, BVF and bone mineral density (BMD) of the tibial diaphysis. These findings reveal that reductions in medullary bone quality might be associated with age-related low estrogen levels and stimulation of osteoclastic bone resorption by parathyroid hormone. Cortical bone quality decreased with enlargement of the Haversian canals and loss of volume, with a longer egg-laying period leading to osteoporosis.

The effect of perch availability during pullet rearing and egg laying on musculoskeletal health of caged White Leghorn hens

A major skeletal problem of conventionally caged hens is increased susceptibility to osteoporosis mainly due to lack of exercise. Osteoporosis is characterized by a progressive decrease in mineralized structural bone. Whereas considerable attention has been given to enriching laying cages, little research has been conducted on providing caged pullets with furnishments, in particular perches. The objective of the current study was to determine if metal perches during all or part of the life cycle of White Leghorns affected hen musculoskeletal health, especially at end of lay. Treatments during the pullet phase (hatch to 16.9 wk) entailed cages with and without perches. Four treatments were used during the laying phase (17 to 71 wk of age). Treatment 1 chickens never had access to perches at any point during their life cycle, typical of egg industry practices in the United States for conventional cages. Treatment 2 chickens had access to perches only during the egg-laying phase, which was from 17 to 71 wk of age. Treatment 3 chickens had access to perches only during the pullet phase (0 to 16.9 wk of age). Treatment 4 chickens had perch access throughout their entire life cycle (0 to 71 wk of age). Musculoskeletal health was assessed by measuring muscle weights, bone mineralization, bone fracture incidence, and keel bone deviations. Muscle deposition of 71-wk-old hens increased when given access to perches as pullets. Bone mineralization of 71-wk-old hens also increased if given perch access as adults. However, the disadvantage of the adult perch was the higher incidence of keel deviations and keel fractures at end of lay. The increase in bone mineralization of the keel bone as a result of perch access during the pullet and laying phases was not great enough to prevent a higher incidence of keel bone fractures at end of lay. Perch redesign and placement of perches within the cage to minimize keel fractures and deviations are possible solutions.

Relationships of a transforming growth factor-beta2 single nucleotide polymorphism and messenger ribonucleic acid abundance with bone and production traits in chickens

Osteoporosis is a serious problem for the laying hen industry with economic, production, and welfare consequences. Transforming growth factor-beta2 (TGFbeta2) has been implicated as an important factor in coupling bone resorption and formation in bone remodeling. The current study was designed to determine if TGFbeta2 was associated with variation in bone mineralization in chickens, using 2 complementary experimental approaches. First, an intronic single nucleotide polymorphism (SNP) present in TGFbeta2 was investigated in an F(2) population to determine its association with bone, growth, and egg traits of importance to the layer and broiler industries. The TGFbeta2 SNP was significantly associated (P < 0.05) with bone mineral density and content. However, these associations became nonsignificant when BW was included as a covariate in analyses. The TGFbeta2 SNP was also significantly associated (P < 0.05) with BW from 1 to 6 wk of age and egg production from 46 to 55 wk of age. To further explore the relationship between TGFbeta2 and bone strength, bone marrow TGFbeta2 mRNA abundance was compared between broiler and layer chickens at 15, 35, and 60 wk of age. Bone and egg traits were measured along with mRNA abundance at each age and found to differ significantly between lines. The TGFbeta2 mRNA abundance was approximately 4-fold greater in broiler compared with layer hens at 15 wk of age but was similar between lines at later ages. Thus, even though the TGFbeta2 SNP will likely not be an effective marker for improving bone strength independently of changes in BW, further research is warranted to investigate the relationship of TGFbeta2 mRNA abundance to bone strength in laying hens.

The effect of pre- and postmolt diets high in n-3 fatty acids and molt programs on skeletal integrity and insulin-like growth factor-I of White Leghorns

This study investigated changes in bone integrity and circulating concentrations of insulin-like growth factor-I (IGF-I) of hens subjected to 2 distinct molting regimens and fed pre- and postmolt diets high in n-3 or n-6 fatty acids. A dual-energy x-ray absorptiometer determined bone mineral density (BMD) of the tibia and humerus of 45 live hens from 62 to 76 wk of age. Densitometric scans were also conducted in excised tibia and humerus at 66, 71, and 76 wk of age. Concentrations of IGF-I were monitored using an homologous RIA at the same ages. The molting treatments consisted of 10 d of fasting + cracked corn for 7 d + pullet developer diet for 10 d or a nonfasting molt (wheat-middlings-based diet for 27 d). Five weeks prior to and after either molt treatment, birds were fed 1 of 2 diets containing dietary n-6/ n-3 fatty acids ratios of 0.6 or 8.0. At the end of the molt (71 wk of age), tibial BMD decreased 30% in fasted and 11% in nonfasted molt regimens, and the fatty acid content of the premolt diet had no effect on the decline in BMD. The BMD of the humerus also decreased during molt with the exception of hens subjected to a nonfasted molt and fed n-3 fatty acid diets in which their BMD values were similar to or greater (at 73 wk of age) than those of controls during the entire experimental period (treatment by bone by age, P < or = 0.0001). Induced molt affected circulating IGF-I concentrations (treatment by age interaction, P < or = 0.0001), and the response was the same regardless of molt regimen (fasting vs. nonfasting) or diet (n-3 vs. n-6 fatty acids). A decrease in IGF-I 54 h postmolt was noted; however, from 13 to 43 d postmolt, all molted birds had elevated IGF-I as compared with controls. In conclusion, a nonfasted molt as compared with fasted molt was less detrimental to bone mineralization; dietary n-6/n-3 fatty acid ratios in the pre- and postmolt diets had little effect on the decline of skeletal integrity during molt, and circulating IGF-I concentrations were affected by molt.

The effect of an induced molt using a nonfasting program on bone mineralization of white leghorns

To determine changes in bone mineralization during molt, 66-wk-old White Leghorns were assigned to either a fasted molting regimen using feed removal for 10 d, followed by the ad libitum consumption of cracked corn for 7 d and a pullet developer diet for 10 d or a nonfasted molting regimen lasting 27 d that included the ad libitum consumption of a diet containing 71% wheat middlings and 23% corn. Both molting regimens restricted light to 8 h/d, and water was provided ad libitum. At 28 d postmolt, hens from both molting treatments were returned to a regular egg-laying diet and 16 h/d of photoperiod. Control hens consumed a regular egg laying diet and were kept on 16 h/d of light throughout the study. Using dual-energy x-ray absorptiometry, bone mineral density (BMD) and bone mineral content (BMC) of the left tibia were measured in 7 live hens per treatment immediately prior to, during, and following the molt. Results showed that by 28 d postmolt, BW loss was 22 and 18% in the fasted and nonfasted molting regimens, respectively (P < or = 0.0001). Compared with premolt values, tibial BMD at 28 d postmolt decreased 35 and 18% in the fasted and nonfasted molt groups, respectively (treatment x age interaction, P < or = 0.0001). Similarly, tibial BMC values decreased 39 and 27% in the fasted and nonfasted molt groups, respectively (treatment by age interaction, P < or = 0.01). The tibial BMD and BMC of controls at 28 d postmolt were similar to premolt values. Recovery in tibial BMD and BMC of fasted and nonfasted hens occurred by 126 d postmolt with values similar to controls. These results suggest that a nonfasted molting regimen is less deleterious to tibial BMD and BMC than a fasted molting regimen.

The effect of an induced molt and a second cycle of lay on skeletal integrity of White Leghorns

The effect of an induced molt and a second egg laying cycle on White Leghorns hen's skeletal integrity was investigated in a series of 3 experiments. Using dual-energy X-ray absorptiometry, bone mineral density (BMD) and bone mineral content (BMC) of the left tibia and humerus were measured in live hens and excised bones and correlated with invasive bone measurement tests, egg traits, and the incidence of broken bones in carcasses of processed hens. The results of all 3 experiments showed that an induced molt was detrimental to skeletal integrity. For hens that were repeatedly scanned throughout the second cycle of lay, the BMD of the humerus never recovered after the molt. Recovery of tibial BMD to premolt values occurred late in the second cycle of lay when egg production was declining. The in vivo BMD scans conducted between 77 and 117 wk of age correlated with bone breaking force and bone ash weight (r = 0.58 and r = 0.65, respectively; P < 0.0001). The percentage of freshly broken bones per bird at the end of processing at 126 wk of age averaged 34% and ranged from 0 to 61%. The incidence of broken bones was negatively correlated with the excised tibial BMD and BMC at 126 wk of age (r = -0.54 and r = -0.53, respectively; P < 0.05). In conclusion, feed withdrawal for 10 d during an induced molt was detrimental to the skeletal integrity of hens, and as BMD and BMC of excised tibia at 126 wk of age decreased in White Leghorns, the incidence of bone breakage increased.

Validation of dual-energy X-ray absorptiometry in live White Leghorns

Dual energy x-ray absorptiometry (DEXA) was evaluated for use as a noninvasive tool to monitor skeletal integrity in live laying hens. The objectives of the current study were 1) to validate the use of DEXA in evaluating bone integrity in live birds as compared with excised bones under a normal nutritional regimen as well as in hens fed varying levels of dietary Ca and 2) to correlate densitometric scans with other bone strength criteria and egg traits. Densitometric scans were conducted on the tibia and humerus of live hens at 10-wk intervals from 17 to 67 wk of age. After each scan, bones were excised from euthanized hens to measure breaking strength characteristics and bone ash (experiment 1). Similar measurements were collected at 38, 48, and 58 wk of age from hens fed hypercalcemic (5.4%), control (3.6%), and hypocalcemic (1.8%) diets from 32 to 58 wk of age (experiment 2). The bone mineral density (BMD) and bone mineral content (BMC) between live and excised bone scans were highly correlated (r = 0.85 and 0.92, respectively, P < 0.0001, experiment 1). Densitometric scans of live birds were positively correlated with bone breaking force and bone ash (r = 0.68 and 0.73, respectively, P < 0.001) with little to no correlation with shell traits. In experiment 2, the excised tibial scan had lower BMD and BMC than the live bird (P < 0.01), whereas no difference was detected in densitometric scans of the humerus. The live and excised BMD and BMC of the tibia (r = 0.87 and 0.82, respectively, P < 0.001) and humerus (r = 0.94 and 0.93, respectively, P < 0.001) were highly correlated. Due to the high correlations between live and excised bone scans and the significant correlations of live scans to more traditional invasive bone measurement tests such as bone breaking force and bone ash, we concluded that DEXA is a useful noninvasive tool for evaluating skeletal integrity in live birds.