Evolution of Hormonal Control of Calcium and Phosphorus Metabolism in Different Hen Breeds During the Laying Cycle

Abstract

The aim of this work was to determine the relationshipbetween the calcium and phosphorus metabolism and the levels of the hormonesinvolved in the regulation of the blood level of these elements in hen.Two groups of hens were used in this work, 22weeks aged each one: White Cornish and White Leghorn. The hens were raised inindustrial system and they were fed according to the technologic diets. Thehens were monitored from 22 to 44 weeks of age  for the evolution of the parathormone, vitaminD, calcium and phosphorus levels in the blood plasma. Blood glucoseconcentration, total lipid, total proteins, albumins, globulins, creatinine,and uric acid were also monitored. Analysis of the hormone evolution relieves apeak of the PTH level in WHL hens, around 30 weeks of age (amounted to 392pg/mL vs. 198 pg/mL in CRN hens). This peak of PTH is behind the laying peakand it is significantly higher in WHL hens versus CRN hens. It was remarkedthat the WHL hens reached the peak of the PTH one week sooner vs. CRN hens. Regarding vitamin D,its plasma level presented a relativelyconstant evolution in CRN breed, whilein WHL it presented an increase around 30 - 32 weeks-of-age up to 142 pg/mL,than it decreased slowly.  Accordingly,in White Leghorn (WHL) hens, the level of calcium (in mg/dL) raised from 9.9 atthe beginning of the laying cycle to 34.4 in the peak of the laying, decreasingthen, to 18.0 toward the end of the monitoring period. In Cornish (CRN) hens,at the same age week, the values of the plasmatic calcium were: 6.2, 12.9 and18.0, respectively. The calcium/phosphorus ratio presented an ascendantevolution in both, WHL and CRN breeds, indicating an increasing of the freecalcium content of the blood plasma. Plasmaalbumins ranged between 16.0 and 20.0 mg/ mL in the WHLhens and between 19.8 and 22.8mg / mL in the CRN hens (PE‚0.01).Uric acid plasma levels have evolved relatively parallel to thelaying percentage, showing anintensified protein catabolism, according to laying percentage, in WHL hens. Bloodglucose and total lipids followed an ascending evolution up to the peak of thelaying, then decreased slowly. Plasma estradiol rose from 22 to 32 - 34week-of-age, reaching a higher level in WHL then in CRH while plasmaprogesterone followed two-week-later and lower peak than estradiol.