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Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
Corresponding author: W. P. Weiss; e-mail: weiss.6{at}osu.edu.
Data from 8 experiments involving 39 diverse dietary treatments and 162 Holstein cows were used to derive equations that estimate manure excretion of P by lactating dairy cows. Within an experiment, diets were formulated to have similar P concentrations and to meet or slightly exceed standard recommendations for P. The data were generated from total collection digestion trials. The only sources of supplemental P used were dicalcium phosphate and monosodium phosphate. The concentration of dietary P ranged from 0.34 to 0.45% of dry matter (DM). Cows varied in milk production (8 to 59 kg/d), DM intake (12.4 to 30.5 kg/d), and P intake (45 to 133 g/d). Apparent digestibility of P averaged 40.4%, fecal output of P averaged 47 g/d, and apparent P retention averaged 4 g/d. Two equations were derived to estimate excretion of P via manure (g/d): 1) Manure P = –2.5 + 0.64 x P intake, and 2) Manure P = 7.5 + 0.78 x P intake – 0.702 x Milk; where P intake is in g/d and milk is kg/d. Both equations were evaluated using literature data, and both equations had acceptable accuracy for field use. The requirements for P of lactating dairy cows from the National Research Council (NRC) were also evaluated, and for most diets, those requirements were adequate based on retention of P.
Key Words: phosphorus • manure • environment
Abbreviation key: TAR = total absorbable requirement, TAS = total absorbable supply
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