Progress 10/15/01 to 10/31/03
Outputs
Dual-energy X-ray absorptiometry (DEXA) was used to determine bone mineral densities (BMD) of the left tibia together with the fibula as well as the humerus of live, unanesthetized birds. We learned that DEXA was a useful tool for the non-invasive evaluation of skeletal integrity in live hens. This conclusion was based on the positive correlations between live bird and excised bone scans (r = 0.73 to 0.94, P < 0.001) as well as between live scans and more traditional invasive bone measurement tests such as bone breaking force (r = 0.58 to 0.68, P < 0.001) and bone ash weight (r = 0.73 to 0.99, P < 0.001). Densitometry effectively detected changes in bone integrity of live birds fed varying levels of dietary calcium. Hens consuming 1.8, 3.6, and 5.4% levels of dietary calcium had BMD of 0.147, 0.157, and 0.176 g/sq cm (SEM = 0.005), respectively (linear effect, P < 0.001). Likewise, bone ash weight, breaking force, stress, modulus of elasticity as well as eggshell
traits also increased linearly in response to increased calcium level in the diet (P < 0.05). We discovered that as BMD decreased in White Leghorns, the incidence of bone breakage increased. The DEXA readings were not dependent on the stage of calcification indicating that scans can be done at any time during the ovulatory cycle. We have monitored BMD in live Leghorn and broiler females during their life cycle. The tibial BMD of White Leghorns and broilers increased as the birds aged from 15 to 65 wk of age with the BMD of the broiler tibia increasing at a greater rate than the Leghorn tibia (line x age interaction, P < 0.0001). A precipitous drop in BMD occurred during an induced molt of Leghorns subjected to 10-d of feed withdrawal, but we learned that a non-fasting molting regimen was less detrimental to skeletal integrity. Therefore, poor bone mineralization is most critical during the molting phase of a hen's life cycle with evidence towards recovery in BMD by 67 days post-molt.
The CV for BMD of Leghorns was greater than 10% after 25 wk of age suggesting that DEXA can be used as an indicator tool in genetic selection with a potential for improving skeletal integrity of birds. By crossing a broiler with an egg line, an F2 resource population of birds was developed and quantitative trait loci (QTL) influencing BMD and other bone traits in chickens have been identified. Our long-term goal is to improve skeletal integrity in egg-type chickens by genetic selection for improved BMD. We are currently searching for positional candidate genes affecting skeletal integrity for potential use in marker-assisted selection programs.
Impacts
Because we have shown that dual energy X-ray absorptiometry may be used in live birds as a diagnostic tool to assess skeletal integrity, a genetic breeding company, Hy-Line International, is considering the purchase of a similar unit to be used specifically for their chicken genetic selection program for the purpose of improving skeletal integrity. The QTL results are significant because they represent the first genome scan for QTL influencing bone traits completed in chickens and demonstrate that genomic regions contribute to variation in bone strength.
Publications
- Onyango, E. M., P. Y. Hester, R. L. Stroshine, and O. Adeola, 2003. Bone densitometry as an indicator of percent tibia ash in broiler chicks fed varying dietary calcium and phosphorus levels. Poultry Sci. 82:1787-1791.
- Hester, P. Y., M. A. Schreiweis, J. I. Orban, H. Mazzuco, M. N. Kopka, , M. C. Ledur, and D. E. Moody, 2004. Assessing bone mineral density in vivo: Dual energy X-ray absorptiometry. Poultry Sci. 83:215-221.
- Schreiweis, M. A., J. I. Orban, M. C. Ledur, D. E. Moody, and P. Y. Hester, 2004. The effect of the ovulatory and egg laying cycle on bone mineral density and content of live White Leghorns as assessed by dual-energy X-ray absorptiometry. Poultry Sci. 83:1011-1019.
- Patterson, P. H., R. M. Hulet, T. L. Cravener, P. Y. Hester, P. J. Kleinman, and A. N. Sharpley, 2004. Heavy tom strains fed low calcium and phosphorus diets supplemented with phytase 2. Impact on litter total P, soluble P and bone integrity. Poultry Sci. 83: (suppl. 1): 143.
- Mazzuco, H., and P. Y. Hester, 2004. Incidence of bone breakage of processed White Leghorn hens monitored for skeletal integrity during the second cycle of egg laying. Poultry Sci. 83: (suppl. 1):152.
- Schreiweis, M. A., P. Y. Hester, and D. E. Moody. 2004. Identification of quantitative trait loci associated with bone mineral density in an F2 generation of a broiler and leghorn cross. Plant and Animal Genome Conference XII, San Diego, CA. January, 2004. (P661). www.intl-pag.org/.
- Schreiweis, M.A., P.Y. Hester, and D.E. Moody. 2004. Quantitative trait loci affecting bone mineral density in the chicken. Poultry Sci. 83: (suppl. 1): 262.
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Progress 10/01/02 to 09/30/03
Outputs
The skeletal integrity of live birds was monitored during the first and second cycles of lay with an induced molt at 76 wk of age. The humerus and tibia of 27 to 35 live chickens of a pedigree line of White Leghorns were scanned repeatedly at 10 wk intervals from 15 to 125 wk of age. The tibia had higher BMD at all ages than the humerus. The greater medullary component of the tibia as compared to the humerus most likely contributed to the higher BMD. Although considered a pneumatic bone, the humerus of some birds has a medullary component. The amount of medullary bone comprising the humerus is highly variable among laying hens ranging from less than 10% to as high as 50%. It is known that the medullary component of the humerus contributes to breaking strength. A peak in BMD occurred at 75 wk of age for both the tibia and humerus during the first cycle of lay. An induced molt at 76 wk of age caused a post-peak decline in BMD for both bones, but the BMD of the tibia
recovered by 105 wk of age with another peak in tibial BMD occurring at 115 and 125 wk of age. Part of the reason for the second peak in BMD at the end of the second cycle of lay was because the birds with lower tibial BMD had died. The 8 dead hens had a mean BMD of 0.159 g/sq cm when averaged over their life span, while the 27 hens that survived to 125 wk had a mean BMD of 0.194 g/sq cm. The humerus, more representative of structural bone, never recovered from the peak BMD observed at 75 wk of age, but BMD values at the end of lay were similar to BMD readings at 65 wk of age. As with the tibia, the life-time BMD average of the humerus of dead birds was lower (0.137 g/sq cm) than that of hens that were alive at 125 wk of age (0.161 g/sq cm). If these hens, which died of natural causes, had lived to 125 wk of age, it is suspected that a decline in BMD of the humerus would have been noted at the end of the second egg laying cycle. The unique medullary component of the avian skeleton
contributed to the lack of an age related decline in BMD. Hens monitored for life cycle changes in BMD were a pedigree line of White Leghorns; therefore, the possibility exists that their bones, especially the humerus, may have a higher medullary component than commercial egg-laying strains of birds. Therefore, we conducted another study with a commercial line of White Leghorns and noted a similar age related increase in tibial BMD with no noted decline in humeral BMD by 60 wk of age. Likewise, we conducted scans using dual energy X-ray absorbtiometry on excised bones of a commercial strain of White Leghorns received from the University of Nebraska. Bones were retrieved from hens at <19, 29, and >70 wk of age. A linear increase in BMD was noted in both the humerus and tibia as the hens aged. The reason for the lack of a decline in BMD in hens during egg laying is perhaps due to the calcium-enriched diets fed during egg production and the endogenous estrogens that stimulate medullary
bone formation. Thus, with densitometric readings for BMD, any structural bone loss that occurs with age in the tibia and perhaps the humerus may be masked by enhanced medullary bone formation.
Impacts
Dual-energy X-ray absorptiometry is a useful quantitative measurement for assessing skeletal status. The medullary component of bone contributes to bone strength; therefore, any nutritional, environmental or genetic factor that improves BMD should also improve bone strength and skeletal integrity and reduce fractures.
Publications
- Moody, D., J. Haynie, M. Schreiweis, and P. Hester, 2003. Identification of SNP in candidate genes for osteoporosis in chickens. Proc. Plant & Ani. Genome Conf. XI, San Diego, CA.
- Schreiwies, M. A., J. I. Orban, M. C. Ledur, D. E. Moody, and P. Y. Hester, 2003. A comparison of bone mineral density in live broilers and White Leghorns. Poultry Sci. 82: (suppl. 1): 99.
- Onyango, E. M., P. Y. Hester, and O. Adeola, 2003. Bone densitometry may be used to predict percent tibia ash in broiler chicks fed varying dietary calcium and phosphorus levels. Poultry Sci. 82: (suppl. 1): 130.
- Kopka, M. N., H. W. Cheng, and P. Y. Hester, 2003. Bone mineral density of laying hens housed in enriched versus conventional cages. Poultry Sci. 82: (suppl. 1):29.
- Hester, P. Y., M. A. Schreiweis, H. Mazzuco, M. N. Kopka, J. I. Orban, M. C. Ledur, and D. E. Moody, 2003. Assessing bone mineral density in vivo: Dual emission X-ray absorptiometry. Poultry Sci. 82: (suppl. 1): 55.
- Mazzuco, H., I. Grader, and P. Y. Hester, 2003. The effect of a feed removal molting program on the skeletal integrity of White Leghorns. Poultry Sci. 82: (suppl. 1): 82.
- Schreiweis, M. A., J. I. Orban, M. C. Ledur, and P. Y. Hester, 2003. A comparison of densitometry with other bone tests in White Leghorns fed varying levels of dietary calcium. Poultry Sci. 82: (suppl. 1): 29-30.
- Schreiweis, M. A., J. I. Orban, M. C. Ledur, and P. Y. Hester, 2003. The use of densitometry to detect differences in bone mineral density and content of live White Leghorns fed varying levels of dietary calcium. Poultry Sci. 82: 1292-1301.
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Progress 10/01/01 to 09/30/02
Outputs
Using a Norland densitometer, we have shown that dual-energy X-ray absorptiometry accurately measured differences in bone mineral density and bone mineral content in live birds fed varying levels of dietary calcium. The bone mineral density and content of both the humerus and tibia increased linearly as hens consumed greater quantities of calcium. Likewise, bone breaking force, stress, and modulus of elasticity increased linearly with increasing levels of dietary calcium. Bone breaking force was significantly correlated with bone mineral density (r = 0.56, P < 0.01). The bone mineral density and content of the tibia and humerus did not change as an egg was being formed in the reproductive tract of the hen indicating that densitometry scans can be conducted at any time of the day. The bone mineral density of the humerus and tibia scanned in live birds did not differ significantly from the bone mineral density of the respective excised bones. We have monitored the bone
mineral density of the humerus and tibia of hens during the first cycle of egg laying and through an induced molt. The bone mineral density of both the humerus and tibia increased as the hens aged up to 75 wk of age followed by a dramatic drop during an induced molt. Recovery of bone mineral density into the second cycle of egg production did not occur until 67 days after the initiation of an induced molt. We are currently monitoring bone mineral density of hens that are in their second cycle of egg production.
Impacts
We have shown that densitometry can be used in live chickens to accurately determine bone mineral density and content. Hens are especially susceptible to osteoporosis during an induced molt. Our long-term research goal is to identify quantitative trait loci influencing bone mineral density in chickens.
Publications
- Schreiweis MA, Orban JI, Ledur MC, Hester PY. 2001. Assessment of densitometry to measure bone mineral content and density in live birds as a tool for monitoring osteoporosis in laying hens. Poultry Sci. 80: (suppl. 1): 94.
- Orban, JI, Hester PY. 2001. Profile of plasma hydroxyproline in laying hens during an ovulatory cycle. Poultry Sci. 80: (suppl. 1):173.
- Schreiweis, MA, Orban JI, Ledur MC, Hester PY. 2002. Assessment of densitometry in the measurement of bone mineral density and content of live White Leghorns fed varying levels of dietary calcium. Poultry Sci. 81: (suppl. 1): 29.
- Schreiweis, MA, Orban JI, Ledur MC, Hester PY. 2002. The effect of the ovulatory cycle on bone mineral density and content in live White Leghorns as assessed by densitometry. Poultry Sci. 81: (suppl. 1):80.
- Franzen, KK, Beck MM, Hester PY, Sarath G, Caceres N. 2002. Calcium mobilization in the aging hen: I. ER-a populations in calcium-regulating tissues and skeletal integrity in three ages of laying hens. Poultry Sci. 81: (suppl. 1): 30.
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