Macromineral digestion by lactating dairy cows: estimating phosphorus excretion via manure.
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.
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691, USA. weiss.6@osu.edu
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Wyatt
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D004063:Digestion; D005260:Female; D007774:Lactation; D008372:Manure / Q000032:analysis*; D008433:Mathematics; D008903:Minerals / Q000378:metabolism*; D010758:Phosphorus / Q000032:analysis* / Q000493:pharmacokinetics; D016226:Phosphorus, Dietary / Q000008:administration & dosage; D012820:Silage; D013025:Glycine max; D003313:Zea mays
D008372:Manure; D008903:Minerals; D016226:Phosphorus, Dietary; D010758:Phosphorus