Response of Early- and Late-Maturing Commercial Leghorn Pullets to Low Levels of Dietary Phosphorus

Abstract

An experiment with a 2 × 2 factorial arrangement of treatments was used to determine differences in responses of early-maturing (EM) and late-maturing (LM) pullets fed low dietary P (.4% total P; LP) and normal dietary P (.7% total P; NP) levels. Six hundred pullets (18-wk-old) were equally and randomly allocated to the LP and NP treatments. Egg production, egg weight, egg specific gravity, and eggshell breaking strength were measured at 26 and 28 wk. When pullets were 28 wk of age, plasma total Ca (TCa), ionic Ca (Ca++), and inorganic P (Pi) concentrations, urine Ca concentrations, and urine pH, bone mineral content (BMC), bone density, total kidney weight, and kidney weight ratio (heavier kidney ÷ lighter kidney) were determined from 15 pullets each from EM-NP, EM-LP, LM-NP, and LM-LP treatments. The pullets with osteoporosis and pullets that died during the experiment were categorized into EM and LM groups.Results showed that LP caused severe adverse effects on LM pullets. The LM pullets fed the LP diet had high plasma Ca++ concentration, low plasma Pi concentration, increased urine Ca concentration, a high incidence of osteoporosis, mild kidney lesions, and elevated mortality compared with pullets subjected to the other treatments. The EM pullets fed the LP diet were also adversely effected by LP, but were less susceptible to osteoporosis and mortality. The LP diet improved eggshell quality, but this beneficial effect was only temporary. The severity of adverse effects of low dietary P was greater for LM than the EM pullets.