Utilization of Phosphorus in Lactating Cows Fed Varying Amounts of Phosphorus and Forage

Abstract

The objective of this study was to determine the effect of dietary forage proportion and P content on fecal P excretion. Four dietary treatments were formed in a 2 x 2 factorial arrangement. The P content was 0.33 or 0.42%, and the forage proportion was 48 or 58% on a dry matter (DM) basis. The neutral detergent fiber content was 27 and 30% for the low and high forage diets, respectively. The P amount was varied by using monosodium phosphate, and the forage amount by changing the proportions of alfalfa silage and corn. The diets were fed to 44 midlactation Holsteins for 14 wk. Fecal P excretion was estimated using Cr marker and grab sampling. Dietary P content did not affect DM intake, milk yield, or milk composition. The P intake averaged 74 and 96 g/d and fecal P averaged 0.69 and 0.92% (DM basis) or 49 and 65 g/d for the low and high P diets, respectively. Thus, reducing dietary P from 0.42 to 0.33% resulted in approximately 25% less estimated fecal P excretion. Increasing dietary forage reduced milk yield (34.0 vs. 36.5 kg/d), but increased milk fat content (3.66 vs. 3.25%). Estimated apparent digestibility of P tended to decrease (31.1 vs. 36.6%) when the forage proportion increased, but most of the change occurred when the diets contained the low amount of P. Overall, the effect of forage proportion on estimated fecal P excretion was small when diets contained 48 or 58% forage, varied by alfalfa silage. Phosphorus intake has a much larger impact on fecal P excretion than forage proportion, and it does not seem necessary to adjust the dietary P content according to the forage proportion to provide the same amount of absorbed P.

Effect of dietary phosphorus content on milk production and phosphorus excretion in dairy cows

“…Similarly, there were no significant differences in milk lactose, fat-corrected milk (FCM), SNF, or SCC ( P  > 0.05). These observations are consistent with previous reports in the literature [16], which indicate that varying dietary P from 0.37 to 0.57% does not affect milk composition.…”

Meta-analysis of factors that affect the utilization efficiency of phosphorus in lactating dairy cows

“…A biological explanation for this result could be that absorbed P in excess of the animal's requirements is extensively recycled through saliva. It has been suggested that dietary NDF content increases salivary P secretion as a result of increased saliva flow caused by increased chewing (Khorasani et al, 1997;Wu et al, 2003), but that the effect of NDF content on salivary P secretion would likely be less at lower levels of dietary P (Wu et al, 2003). At low P intake, the animal's priority is rumen function at the expense of bone or salivary P (Puggaard et al, 2011).…”

“…This database subset comprised data from lactating dairy cows from 25 studies (Martz et al, 1990;Morse et al, 1992;Spiekers et al, 1993;Delaquis and Block, 1995;Khorasani et al, 1997;Knowlton et al, 2001Wu et al, 2001Wu et al, , 2003Knowlton and Herbein, 2002;Guyton et al, 2003;Kebreab et al, 2005;Kincaid et al, 2005;Shore et al, 2005;Wu, 2005;Ekelund et al, 2006;Kamiya et al, 2006a;Knowlton et al, 2007;Dann et al, 2008;Moreira et al, 2009;Myers and Beede, 2009;Taylor et al, 2009;Van Straalen et al, 2009;Herrera et al, 2010;Puggaard et al, 2011) and included 130 treatment means. The response variable of interest was P excretion in the feces, both in grams per day and as a fraction of P intake.…”

El fósforo en los sistemas ganaderos de leche.

“…Este y otros estudios indican una relación directa entre el consumo de fósforo y su excreción. Wu et al (2003) por ejemplo, encontraron que reducir la concentración de fósforo en la dieta de 0,42 a 0,33% resultó en aproximadamente 25% menos fósforo excretado estimado en las heces. Por su parte Cerosaletti et al (2004), al implementar estrategias para disminuir el contenido de fósforo en las dietas, redujeron la excreción de este elemento en un 33%.…”