Published in Scientific Works. Series C. Veterinary Medicine, Vol. LIX (1)
Written by Claudia PREDA, Nicolae DOJANA
It was determined the evolution of the levels of calcium and phosphorus from blood plasma in White Plymouth Rock hens (a hen breed with high egg production) and White Cornish hens (a hen breed with a low egg production) during the laying cycle, beginning from 22 weeks age up to 40 weeks of age. Parallel, it has been monitored the plasma evolution of the parathyroid hormone (PTH) and vitamin D levels, and the evolution of the following blood parameters: total protein, albumin, and uric acid. The results relive significant differences, according to the breed, concerning the parallel raising of the plasmatic calcium levels and the laying egg percent. Thus, in Plymouth Rock (PLR) hens, the level of calcium (in mg/dL) raised from 10.5 at the beginning of the laying cycle to 33.3 in the peak of the laying, decreasing then, to 30.9 toward the end of the laying cycle. On the other hand, in Cornish (CRN) hens, at the same moments, the values of the plasmatic calcium were: 8.8, 22.5 and 20.4, respectively. The calcium/phosphorus ratio presented an ascendant evolution in both, PLR and CRN breeds, indicating an increasing of the free calcium content of the blood plasma. Plasma albumins ranged between 17.2 and 22.2 mg / mL in the PLR hens and between 19.8 and 22.8 mg / mL in the CRN hens, with significant differences between groups. Uric acid plasma levels have evolved relatively parallel to the laying percentage, showing an intensified protein catabolism, according to laying percentage, in PLR hens. Analysis of the hormone evolution relieves a peak of the PTH level in PRL hens, around 32 weeks of age (amounted to 353 pg/mL). This peak of PTH is behind the laying peak and it is significantly higher in PLR hens than in CRN hens (185 pg/mL at the age of 36 weeks). Regarding vitamin D, its plasma level presented a relatively constant evolution in both hen breeds, seeming to be not influenced by breed or high metabolic requirements that characterize a lay peak. It can be concluded that the high demands of calcium and phosphorus export during the laying cycle in hens with high egg production are supported by high levels of PTH, the main hormone involved in regulating the homeostasis of these two minerals.
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