  Environmental temperature (ET) often changes the nutrient intake/output for
layers. Changing feed formulations based on ET may need to be utilized to
obtain optimum performance, shell quality and bone status. This study was
conducted to investigate the effects of temperature, Ca intake, non-phytate P
(NPP) intake and in vitro limestone solubility (LS) on egg-shell quality and
bone status in commercial White Leghorn hens. Egg mass and shell weight per
unit surface area (SWUSA) decreased with increasing ET (p lower than 0.05),
especially when ET was 29.7 C (cycling mean ET)or a constant ET was 32.2 C.
Feeding layers a low soluble larger particle size limestone instead of a highly
soluble limestone produced beneficial effects for SWUSA at the thermoneutral ET
(21.1 C) but the beneficial effect was less or disappeared when ET was higher
than 26.6 C in EXP 1 and 2. Feeding layers 245 and 353 mg NPP/h/d supported
satisfactory bone status at 21.1 C, however layers housed at higher than 30 C
needed an additional intake of 50 mg NPP/h/d to support bone integrity. Results
of EXP 1 and 2 indicates that 48 week old layers housed in thermoneutral or
warmer ET require a minimum of 4.2 g Ca/h/d for maintaining optimum shell
quality and bone integrity. Feeding low LS (34.1% in vitro solubility) improved
egg shell quality only for hens housed in thermoneutral ET (21.1 C) and did not
improve egg shell quality at higher ET (constant or cycling). Daily NPP intake
of 245 and 353 mg/h/d supported optimum egg production and bone status at 21.1
C, respectively. A higher NPP and Ca intake may be required for bone status
compared to egg production, especially in older hens.
