الكاتب: Multiple References

Yearling crossbred steers (n = 60; 386 kg) were individually fed in a completely randomized experimental design to determine their P requirement. Treatments were in a factorial arrangement with two levels of Ca (.35 or .70% of DM) and five concentrations of P (.14, .19, .24, .29, or .34% of DM). The finishing diet consisted of 34.5% dry-rolled corn, 22.5% brewers grits, 22.5% corn bran, 7.5% ground corncobs, 5% molasses, 3% fat, and 5% supplement. Supplemental P was provided as monosodium phosphate and Ca as limestone. Ash content was determined on the first phalanx bone from the lower front legs following slaughter, and rib bone breaking strength was determined with an Instron Universal Testing Machine. Carcass maturity and shear force were also evaluated on wholesale rib Key Words: Phosphorus, Requirements, Bones, Cattle, Carcasses, Performance 1999 American Society of Animal Science. All rights reserved. J. Anim. Sci. 1999. 77:2832–2836 Introduction Phosphorus is an expensive supplement in the diets of feedlot cattle and may be deleterious to the environment (Spears, 1996). Numerous studies have been conducted to elucidate the P requirement for maintenance (Lofgreen et al., 1952; Call et al., 1986) and gain (Wise et al., 1958; Miller et al., 1987; Jackson et al., 1988) of cattle. Most research has concentrated on young (< 5 mo), lightweight (< 200 kg) calves that have elevated requirements due to bone growth and maturation. Ruminants utilize 60 to 70% of the organic P they ingest, which in grains is primarily bound as phytate P (Nys et al., 1996). The phytate is hydrolyzed by phytase produced by ruminal microbes (Morse et al., 1992). Because ruminants can utilize organic (phytate) P, and most experiments have been conducted with younger calves gaining less than .5 kg/d, P requirements for finishing yearling cattle deserve further attention. 1 Published with the approval of the director as paper no. 12419, journal ser., Nebraska Agric. Res. Div. 2 To whom correspondence should be addressed. Received November 30, 1998. Accepted April 9, 1999. 2832 cuts. Because no interactions between Ca and P levels were detected, only main effects are presented. Daily gain, DMI, and feed efficiency were not affected by dietary P concentration or P intake. Bone ash (g or g/ 100kg BW) and rib bone breaking strength were also unaffected by dietary P. Feeding .7% Ca decreased (P < .06) ADG and efficiency compared with feeding .35% Ca. Neither dietary Ca nor P had a significant effect on tenderness (shear force), skeletal maturity, or overall maturity. These results indicate that the P requirement for finishing yearlings is .14% of diet DM or less and that supplementing P above levels supplied by basal ingredients in many grain-based finishing diets is not necessary.