Effects of flesh attachment on bone breaking and of phosphorus concentration on performance of broilers hatched from young and old flocks.

Two experiments were conducted to 1) assess any differences on breaking force in bones with or without flesh attachment and 2) determine the effects of dietary nonphytate phosphorus (npP) concentration, maternal flock age, and chick sex on live performance and tibia strength of broilers. For experiment 1, sixty chicks were placed in battery cages and selected weekly for removal of both tibiae (15 chicks/wk). Raw flesh was either completely cut from the bone or left intact and broken using a texture analyzer. For experiment 2, Ross 708 chicks (1,220) were hatched of 25- and 65-wk-old breeder flocks, separated by sex, vaccinated, and placed on used bedding across 64 floor pens (18 males or 17 females/pen, 8 repetitions/treatment). Through 28 d, all birds were fed corn-soybean meal diets (22% CP, 3,086 kcal/kg) adequate in all nutrients but npP, which was included at either 0.35 or 0.50%. Individual BW and pen feed consumption (FC) were recorded weekly and corrected for mortality. Each week, 24 birds/treatment were killed for tibia evaluation. Experiment 1 resulted in no differences in breaking force, whether flesh remained or was removed from the bone. In experiment 2, BW was increased with an increase in npP (P<0.001) at the end of the experiment. Both BW and FC were increased (P<0.001) from 0 to 28 d of age in chicks from the 65-wk-old breeder flock. Males had increased (P<0.001) final BW, FC, and tibia breaking forces. Breaking forces were also improved (P<0.001) when npP was increased or chicks were hatched from older breeder flocks. Interactions were present (P<0.05) for npP concentrationx25-wk breeder flock 7- to 21-d BW gain (BWG) and 0- to 28-d FC, npP x chick sex 7- to 14-d BWG and 21- to 28-d feed conversion ratio, and breeder flock age x chick sex 0 d BW and 7- to 14-d BWG. These results indicate that broiler growth and performance can be affected by maternal flock age, chick sex, and dietary npP.