Egg-shell deposition and blood plasma inorganic phosphorus concentration in individual laying hens

Dietary phosphorus supply, egg-shell deposition and plasma inorganic phosphorus in laying hens

1. In 2 experiments the effects of dietary phosphorus on relationships between plasma inorganic phosphorus concentration (Pi), shell and egg production and depletion states were measured in brown laying hens. 2. In a 12-week experiment dietary phosphorus concentrations from conventionally deficient (1.6 g non-phytate-phosphorus (PNP)/kg) to moderate excess (3.9 g PNP/kg) had little effect on egg and shell production, although there was evidence that plasma Pi concentration, when not influenced strongly by shell formation, reflected dietary phosphorus content. 3. Among birds at each dietary phosphorus concentration there was a negative linear relationship between shell weight of early eggs in the sequence and plasma Pi concentration. The relationship was apparently not affected by dietary phosphorus concentration. 4. Continued feeding of the deficient diet to 61 weeks of age did not have effects on body weight, egg and shell production, other than those associated with age, but plasma Pi and bone measurements indicated marginal phosphorus depletion. 5. In another experiment excessive dietary phosphorus (11.9 g PNP/kg) fed in a cross-over design caused small adverse effects on shell production, increased food intake and body weight and increased plasma Pi content, while there was no relationship between shell weight and plasma Pi concentration. 6. The results are consistent with an indirect effect of plasma phosphorus accumulation on shell formation, probably via an inhibitory effect on skeletal calcium release, in addition to any effect of excess dietary phosphorus on intestinal calcium availability. 7. Phosphorus requirement and status in the laying hen are complicated by the failure to recognise the contribution of digestible phytate-phosphorus to the available phosphorus supply.

Further investigations on the effect of dietary manipulation of protein, phosphorus, and calcium for reducing their daily requirement for laying hens

Experiments were conducted to determine the possibility of reducing the daily requirement of laying hens for Ca, available P (AP), and protein by providing the hens with adequate levels of these nutrients only during those hours of the day that the physiological need for these nutrients for formation of various components of the eggs are increasing. The results of the Ca experiment indicated that the daily Ca requirement cannot be reduced by providing the hens with adequate levels of Ca during the afternoon (1500 to 2100 h) and inadequate Ca level during the morning (0500 to 1500 h). Providing the hens with most of the daily Ca need during the afternoon did not have a beneficial effect on shell quality as compared to the control group that received a diet with 3.5% Ca during the morning and the afternoon. On the other hand, inadequate Ca intake during the afternoon adversely affected shell quality as compared to the control group (P < 0.05). The AP experiment indicated that egg production performance and shell quality can be maintained satisfactorily as long as the daily intake of AP is adequate, regardless of whether most of the AP is consumed during the morning or the afternoon. Egg production and shell quality of hens fed a diet with 0.4% AP during the morning and 0.1% AP during the afternoon or 0.1% AP during the morning and 0.4% AP during the afternoon were not different than the control group that received a diet with 0.25% AP during the morning and the afternoon. The results of two protein experiments failed to indicate that egg production performance of laying hens can be maintained satisfactorily by providing them with an adequate level of protein (16%) only during the morning and inadequate level of protein (10%) during the afternoon or, conversely, compared to the control group that received a diet with 16% protein both during the morning and afternoon (P < 0.05). The supply of adequate protein with sufficient amino acids, during the morning and the afternoon, was required for satisfactory maintaining egg production performance. Under the conditions selected for the conduct of this study, the results of the current experiments, combined with those of a previous report, failed to support the hypothesis that satisfactory performance may be maintained by providing the hens with adequate levels of protein, AP, and Ca only during those hours of the day when the physiological need for these nutrients for formation of various components of the egg are increasing.