Phosphorus requirement and excretion of finishing beef cattle fed different concentrations of phosphorus1

Abstract

Phosphorus is an expensive nutrient to supplement, and excess may lead to manure P challenges. Therefore, minimizing dietary P to meet requirements is important. Two experiments were conducted to determine the P requirement of finishing cattle (Exp. 1) and to evaluate the effects of feeding different P concentrations on the quantity and route of P excretion (Exp. 2). In Exp. 1, 60 heifers (BW = 278 kg +/- 17 kg) were individually fed 1 of 5 dietary P concentrations (0.10, 0.17, 0.24, 0.31, or 0.38% P). Cattle performance, plasma P concentration, bone characteristics, and bone P concentration were used to determine the P requirement. Intake and ADG increased quadratically (P < 0.01) as dietary P increased. Plasma P in heifers receiving the 0.10% treatment was less (P < 0.01) than the other treatments and suggested that these heifers were experiencing a P deficiency. Total ash weight of the phalanx bones increased linearly (P < 0.01) as dietary P increased. In Exp. 2 using a 5 x 5 Latin square design, 5 different diets varying in P concentration (0.12, 0.27, 0.42, 0.30, and 0.36% P) were fed to steers to evaluate route and quantity of P excreted. Steers excreted little (1.78 g/d on average) P in the urine as a percentage of total P excretion. Steers on the 0.12% P diet excreted very little P in urine (0.50 g/d). Excretion of P was less (P < 0.05) for the cattle fed 0.12% P compared with all other treatments. Results from cattle performance, plasma P concentrations, and bone characteristics indicate that the heifers fed 0.10% P were experiencing a deficiency and the P requirement of finishing heifers is between 0.10 and 0.17% P. Dietary P concentrations of 0.10 to 0.17% P resulted in decreased P excretion. Supplementation of mineral P is unnecessary in grain-based feedlot diets because dietary P will greatly exceed the requirements (<0.17%).

Nutrient Requirements of Zebu and Crossbred Cattle - BR-CORTE

“…The proposed equation for P excretion (Geisert et al, 2010) did not correctly estimate the excretion of P for BR-CORTE data (P < 0.05; Table 12.1); however, a high CCC value was obtained. The lack of accuracy in estimating the excretion of P can be explained by genetic factors, because animals used by Geisert et al (2010) differ from Zebu and crossbred animals used under tropical conditions.…”

“…Prior to generating new equations for nitrogen and phosphorus excretion, prediction equations of nitrogen and phosphorus excreted (Geisert et al, 2010;Waldrip et al, 2013;Dong et al, 2014) as proposed by BCNRM (2016), were tested for appropriateness for these database. The tested equations are presented below.…”

“…Urinary N (g/d) = -21.18 + 0.56 × NI [Waldrip et al, 2013] Fecal N (g/d) = 24.28 + 0.15 × NI [Waldrip et al, 2013] Urinary N (g/d) = -14.12 + 0.51 × NI [Dong et al, 2014] Fecal N (g/d) = 15.82 + 0.20 × NI [Dong et al, 2014] Urinary N (g/d) = 2.39 + 0.55 × NI -3.36 × DMI [BCNRM, 2016] Total P (g/d) = 0.82 + 0.57 × P intake [Geisert et al, 2010] where NI is nitrogen intake (g/d); DMI is dry matter intake (kg/d) and P intake is phosphorus intake (g/d). The equations proposed by BCNRM (2016) were tested using the BR-CORTE (2016) database.…”

“…The lack of accuracy in estimating the excretion of P can be explained by genetic factors, because animals used by Geisert et al (2010) differ from Zebu and crossbred animals used under tropical conditions. Thus, is necessary to develop equations consistent with the environmental and genetic conditions in Brazil.…”

“…The excess of phosphorus in the diet causes an increase in urinary excretion and in concentration in saliva which causes increase in phosphorus lost in feces (Underwood and Suttle, 1999). Phosphorus fecal excretion is a function of the intake (Geisert et al, 2010), showing a positive correlation.…”