Diurnal Phosphorus Rhythms in Laying Hens

Hy-Line Brown laying hens were fed with a regular diet (corn-soybean meal-based; containing 0.32% non-phytate phosphorus (NPP); Table 1) start from 35 weeks of age. On the last day of age 40 weeks, a total of 60 hens that laid eggs between 07:30−08:30 were randomly selected to evaluate the daily phosphorus rhythms. Of them, 45 hens were euthanized for sample collection, and the other 15 hens were used to study the feed intake and calcium/phosphorus excretion rhythms. For sample collection, the 45 hens were sampled according the oviposition cycle: at oviposition, at 6, 12, 18 h post-oviposition, and at the next oviposition, respectively, with 9 hens sampled at each of the time point. The following samples were collected: blood (for serum), uterine (stored at −80 ℃, for Western-blotting analysis), femur (in 4% paraformaldehyde, for histological analysis) and kidney (stored at −80 ℃, for Western-blotting analysis). For the other 15 hens, the feed intake was recoded and the excreta was collected at the following intervals: from oviposition to 6 h post-oviposition, from 7 to 12 h post-oviposition, from 13 to 18 h post-oviposition, from 19 h post-oviposition to the next oviposition.Table 1

Composition and nutrient concentrations of basal diet (%, unless noted, as-is basis)

Item	Low phosphorus	Regular phosphorus
Ingredients
Corn	56.69	56.69
Soybean meal	25.77	25.77
Distillers dried grains with solubles	4.00	4.00
Calcium carbonate	9.73	9.04
Dicalcium phosphate	-	1.15
Soybean oil	1.51	1.51
Sodium chloride	0.26	0.26
DL-Methionine	0.18	0.18
Choline chloride	0.15	0.15
Montmorillonite	0.71	0.25
Premix1	1	1
In total	100.00	100.00
Nutrient levels
Metabolizable energy, kcal/kg (calculated)	2,600	2,600
Crude protein (calculated)	16.5	16.5
Total phosphorus (calculated/analyzed)	0.34/0.34	0.53/0.49
Non-phytate phosphorus (calculated)	0.14	0.32
Calcium (calculated/analyzed)	3.50/3.47	3.50/3.52

¹Provided per kilogram of diet: manganese 60 mg, copper 8 mg, zinc 80 mg, iodine 0.35 mg, selenium 0.3 mg, vitamin A 8000 IU, vitamin E 30 mg, vitamin K₃ 1.5 mg, thiamine 4 mg, riboflavin 13 mg, pantothenic acid 15 mg, nicotinamide 20 mg, pyridoxine 6 mg, biotin 0.15 mg, folic acid 1.5 mg, and cobalamin 0.02 mg