Phosphorus Concentration and Solubility in Dairy Feces: Variability and Affecting Factors

Abstract

Recent data from phosphorus (P) feeding trials have demonstrated that P concentration in dairy feces is directly affected by P levels in diets and that farm P surpluses as well as potential environmental losses can be reduced through dietary manipulation. The current study was conducted to examine the variability of fecal P under farm conditions and to elucidate factors affecting the concentration and solubility of fecal P. Feed and fecal samples from >30 commercial dairies in the Northeast and Mid-Atlantic regions were analyzed. Dietary P concentrations ranged from 3.45 to 5.78 g/kg of feed DM (DM), and P determined in acid digests (TP) of feces from 5.84 to 12.84 g/kg of fecal DM. On average, 50% of fecal TP was water soluble; of the latter, 83% was inorganic (Pi). Across-farm variability (n=33) had CV averaging 18.9% for fecal TP and >20% for Pi and total P (Pt) in water extracts. Within-farm variability based on multiple samples per herd had the same magnitude as across-farm and was independent of sample numbers from individual farms (n=7 to 30). Of all fecal parameters determined, pH and DM had the lowest variability (CV <10%), water-soluble Pi, Pt, and Ca the highest (CV of 20 to 30%), and total P, Ca, and Mg determined by acid digests were intermediate (CV 10 to 20%). Water-soluble Pi concentrations determined in dried-ground fecal samples were lower than in wet samples. The drying-grinding process changes Pi solubility and the change is not linear. This study confirms that dietary P concentration is the dominating factor affecting fecal P excretion; however, Ca concentration, DIM, and fecal pH also made small, but statistically significant contributions, although some of the mechanisms remain to be thoroughly investigated.

Drying Poultry Manure for Pollution Potential Reduction and Production of Organic Fertilizer

“…Akinremi et al (2003) achieved the lowest concentrations of phosphorous in poultry, cattle and pig manure upon drying at 105°C as appose to freeze-dried and air-dried samples (30°C). Chapuis-Lardy et al (2004) noted lower concentrations of phosphorous in dried feces as appose to wet dairy feces. Tagoe et al (2008) noted that poultry manure that has been carbonized at 500°C has a higher phosphorus content (18.17 g/kg) available than in dried poultry manure (4.47 g/kg).…”

Effect of Drying on Phosphorus Distribution in Poultry Manure

“…Freeze-and 228C-dried samples of PM-1 and PM-3 also had higher H 2 O-extractable P i than undried manures. Drying and grinding have been reported to change P i solubility in dairy manure, resulting in lower H 2 O-extractable P i in 658C-dried material (Chapuis-Lardy et al 2004). Very little change was observed in H 2 O-soluble P o with drying.…”

“…Akinremi et al (2003) examined P tot concentrations of freeze-dried, air-dried (308C), and 1058C-dried organic amendments (poultry, cattle, and pig manure) and found that 1058C-dried samples had lower P tot concentrations than manures dried under other conditions. In addition, Chapuis-Lardy et al (2004) reported lower water-soluble P i concentrations in dried dairy manure than in fresh wet feces from a diverse group of commercial dairy farms in the northeastern United States.…”

Determinations of feed–milk–manure relationships on grazing-based dairy farms

“…For lactating dairy cows fed in confinement, strong positive relationships have been determined between concentrations of P in diets and concentrations of P in dung (Wu et al, 2000;Powell et al, 2001and 2002Dou et al, 2003;Chapuis-Lardy et al, 2004;Satter et al, 2005). In the present grazing study, however, no significant relations were determined between concentrations of P in diets and concentrations of P in dung.…”