Factors affecting the transfer of calcium (45Ca) from the hen's diet to the egg shell

Lack of response of laying hens to relative humidity at high ambient temperature

1. The effects of relative humidity (rh=40% to 70%) at high ambient temperature (Ta) on the performance of laying hens at different ages (8 to 10 months, Trial 1; and 16 to 18 months, Trial 2) was evaluated. Laying hens were exposed to 25 degrees C (control) for 3 weeks and thereafter acclimated for 1 week to 35 degrees C and 4 different rh. 2. Body weight declined significantly in young and older hens exposed to 60% or 70% and 70% rh, respectively: Food intake declined with increasing Ta, except in the case of older hens exposed to 60% rh, for which it remained relatively constant. Water consumption, however, increased with increasing Ta but the increase was significant in young hens exposed to 70% rh only. 3. Egg production was not affected by the changes in Ta. However, a decrease in egg production was observed in older hens exposed to 60% rh. 4. Egg weight (EW), shell weight (SW) and shell thickness (ST) were significantly reduced by exposure to elevated Ta, whereas % breakage significantly increased. In young hens, a response to rh was exhibited in ST which was significantly higher in hens exposed to the low rh (40% to 45%) than in those exposed to the highest rh (70% to 75%). 5. It can be concluded that Ta is the main environmental factor affecting young and older laying hens while the effect of rh is minor.

Environmental heat stress does not reduce blood ionized calcium concentration in hens acclimated to elevated temperatures

Changes in blood concentrations of ionized calcium and total calcium were measured in broiler breeder hens (42 wk old) relative to egg cycle and environmental temperatures. Two environmental temperature treatments were used: 1) temperature cycled daily from a low of 10 C at 0300 h to a high of 25 C at 1600 h; and 2) temperature cycled from a low of 21 C at 0300 h to a high of to a high of 39 C at 1600 h. Serial blood samples were collected from five laying hens per temperature treatment via cutaneous ulnar vein cannula beginning at the time of oviposition and every 4 h thereafter until the next oviposition. Neither blood concentration of ionized calcium nor total plasma calcium was affected by temperature. Results suggest that the supply of calcium available in blood for shell deposition is not diminished in hens acclimated to high environmental temperatures.

Nutritional and environmental factors involved in egg shell quality of laying hens

1. Two experiments were conducted to assess the effects of lighting regime, dietary calcium source and sodium bicarbonate on production variables and egg shell quality of White Leghorn hens. In both experiments, hens were assigned to one of three lighting programmes that provided evening, morning or intermittent (midnight) lighting supplements in addition to natural daylight. Experimental diets used in the first study were formulated to contain (1) ground oyster shell flour, (2) limestone flour, or (3) and (4) the same +2/3 of the calcium source as hen-size oyster shell grit. The same 4 diets plus those containing hen-size limestone or hen-size limestone and oyster shells were used in experiment II. Additionally, diets in the first experiment contained either 0 or 10 g/kg sodium bicarbonate. 2. Hen-day egg production and food consumption were not affected by any of the experimental treatments. Hens fed on oyster shell diets or exposed to intermittent lighting regimes laid eggs of the highest specific gravity. Shell quality, as measured by specific gravity, was not affected by the addition of dietary sodium bicarbonate. 3. As expected, elevated temperatures (greater than 32 degrees C) significantly reduced egg shell quality. However, this effect was variable particularly in experiment II which used younger hens. 4. The shell quality of eggs from hens exposed to intermittent lighting in experiment II was significantly higher in each of the 4 sampling periods: morning (08.00-12.00), afternoon (12.00-16.00), evening (16.00-20.00) and night (20.00-08.00). 5. It is suggested that midnight lighting programmes provide a means of supporting egg shell quality of older laying hens during the summer months without a significant reduction in egg production.

Evaluation of the dietary interaction of calcium and phosphorus in the high producing laying hen

1. In a 6 x 7 factorial experiment using 2688 22-week-old laying hens of the Lohmann-SL strain kept in cages (4 birds/cage), diets containing six calcium (20, 25, 30, 35, 40, 45 g calcium/kg) and seven phosphorus concentrations (3.2, 4.2, 5.2, 6.2, 7.2, 8.2, 16.2 g total phosphorus/kg (Pt)) were combined orthogonally. The resulting 42 treatments were replicated 8 times so that a replicate consisted of a double cage of 2 x 4 hens. The experiment lasted 40 weeks (10 x 28 days). 2. The experimental diets, based on maize and soyabean meals contained 11.5 MJ metabolisable energy/kg and 175 g/kg protein. Different dietary calcium and phosphorus contents were obtained by substituting oat hulls with limestone and dicalcium phosphate. 3. Mortality, egg production, egg weight, egg mass, food intake and food conversion efficiency were determined as well as the breaking strength, thickness of shells and the percentage of eggs with defective shells. 4. All responses measured were significantly influenced by the variance sources (calcium, phosphorus, interaction). Most of the production traits responded asymptotically to increasing dietary phosphorus concentration, the greatest increases or decreases generally being seen between 3.2 and 5.2 g Pt/kg. Further but weaker increases were seen between 5.2 and 8.2 or 16.2 g Pt/kg. 5. Increases in dietary calcium content always resulted in curvilinear responses. In all cases optimal effects were obtained with diets containing 25 g calcium/kg and the worst values at 45 g calcium/kg. The interaction between calcium and phosphorus was recognised by strong performance depressions and a high mortality at combinations of the lowest phosphorus concentration (3.2 g/kg) with high calcium contents (35 to 45 g/kg). These were largely offset by increasing dietary phosphorus. Thus, between 7.2 and 16.2 g Pt/kg and 25 and 45 g Ca/kg a plateau was formed where only small differences in egg production were observed. 6. From the three egg shell characteristics measured, breaking strength and shell thickness responded differently to the percentage of eggs with defective shells. While breaking strength and shell thickness were respectively negatively and positively influenced by increasing dietary phosphorus and calcium contents, both elements affected the proportion of eggs with defective shells.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium balance in the quail (Coturnix coturnix japonica). 1, Influence of sex and diethylstilbestrol

Young adult male and laying female quail, fed with a diet containing 2.64% Ca and 0.70% P, were used to study nutritive utilization, corporal calcium retention and endogenous excretion, calcemia, laying and properties of the egg (including the shell structure), mineralization of the femur bone, as well as the influence of diethylstilbestrol upon these parameters. The coefficient of nutritive utilization (C.N.U.) in the female was high and logically superior to that of the male, while the corporal retention was quite similar for both sexes. Most of the Ca absorbed (81.8%) and not excreted in urine, went to the egg and only 18.2% remained in the body. The diethylstilbestrol caused a big reduction of the C.N.U. in the female, but not in the male, parallel to an inhibition of laying, and an increase of corporal retention of used calcium. In both sexes the calcemia surprisingly increased, and the calcium level of the femur bone was higher, and even though the cortical osseous zone was slightly wider, the effect of treatment was noticeable, particularly in the medular tissue, which incremented in the female and appeared in the male. When quail were fed a calcium-restricted diet, the endogenous excretion of this mineral was small in the case of the female and significantly smaller in the male. This situation suppressed egg laying and resulted in a clearly decreased bone mineralization. The ingestion of diethylstilbestrol before feeding a diet poor in calcium provoked an increase of the endogenous excretion of calcium in both female and male quail.