Phosphorus Partitioning During Early Lactation in Dairy Cows Fed Diets Varying in Phosphorus Content

Abstract

The effect of dietary P content on P partitioning and excretion during early lactation was evaluated in 13 cows fed diets containing 0.34 (no supplementary P), 0.51, or 0.67% P. All cows were fed a common pre-partum total mixed ration (TMR) (0.28% P), followed by common TMR (0.51% P) for 7 d post-partum. On day 7, cows were randomly assigned to one of the three dietary P treatments. All treatment diets contained 16.6% CP, 15.2% ADF, 26.3% NDF, and 0.74% Ca. Total collections of milk, urine, and feces were conducted during weeks 3, 5, 7, 9, and 11 of lactation. Average body weight (591 kg), milk yield (47.9 kg/d), and DMI (25.2 kg/d) throughout the 10-wk trial were not affected by dietary P content. With increasing dietary P, however, linear increases in P intake (84.7, 135.2, and 161.5 g/d), fecal P (42.3, 87.5, and 108.6 g/d), urinary P (0.32, 1.28, and 3.90 g/d), and total P excretion (42.6, 88.8, and 112.5 g/d) were observed. Apparent P digestibility (49.0, 34.4, and 32.8% of P intake) decreased quadratically with increasing dietary P. Phosphorus balance was highly variable, but cows fed the 0.34% P diet were in negative P balance longer than were cows fed diets containing 0.51 or 0.67% P. With increasing dietary P, serum concentrations of inorganic P increased linearly, but serum Ca and Mg concentrations decreased. Increasing dietary P increased fecal and urinary P excretion in early lactation cows. Increased duration of negative P balance and changes in blood mineral concentrations suggest that cows fed low P diets mobilized more P from body reserves than cows on medium- and high-P diets.

Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 2. Health, fertility, bone phosphorus reserves and nutrient utilisation

“…Only a trace of P was excreted in urine and this agrees with the findings of previous studies involving ruminants (Wu et al, 2000;Valk et al, 2002;Knowlton and Herbein, 2002;Ekelund et al, 2006), and reflects the fact that urine only becomes a significant excretory route for P when diets contain excessively high P levels. Phosphorus excreted in milk was unaffected by treatment and this reflects the fact that neither milk output nor milk P content was affected by dietary P level.…”

“…While the apparent digestibility of P increased with cows offered the low P diet in year 2, in common with the findings of Knowlton and Herbein (2002) and Ekelund et al (2006), the apparent digestibility of P was unaffected by dietary P level in year 4, in common with some of the observations by Valk et al (2002). The inconsistent effect of dietary P level on the apparent digestibility of P appears to be largely due to differences in P retention between the 2 years.…”

“…However, resorbed bone P has an important role to play in meeting the P requirements of dairy cows, especially in situations where dietary P is inadequate. On the basis of an extrapolation of data for beef cattle, Wu et al (2001) suggested that a 600-kg dairy cow could mobilise between 600 and 1000 g P in early lactation, while Knowlton and Herbein (2002) observed that between 5 and 25 g P/day was mobilised from body reserves during the first few weeks of lactation. Indeed, the importance of bone resorption is highlighted within the UK P-feeding recommendations (AFRC, 1991), which justifies the absence of a safety margin by suggesting that the skeleton should be relied upon to provide the necessary 'elasticity' between supply and demand.…”

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

“…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.…”

“…However, effects of nutritional factors other than P intake on efficiency of P use are less evident from the literature and warrant further investigation. In addition to dietary factors, animal factors including parity (Knowlton et al, 2001), lactation stage (Knowlton and Herbein, 2002;Ekelund et al, 2006), and milk production level (Valk et al, 2002) may contribute to variation in use of dietary P, through direct or indirect effects. An additional issue may be variation in the P content of milk but infor-mation related to this variation is scarce (Wu et al, 2000).…”