Use of Fecal Samples as a Tool to Monitor Phosphorus Excretion in Lactating Dairy Cows

Abstract

ABSTRACT Lactating Holstein cows were used to determine if disrupting their TMR intake by feeding a top-dress of alfalfa hay affected the diurnal concentration of P in feces and the usefulness of fecal P to monitor P excretion. All cows were fed the control TMR at 1400 h daily, but treatment cows were fed 2.27 kg (DM) of alfalfa hay at 0700 h. Cows had ad libitum access to feed except between 0800 to 1000 h and 1100 to 1400 h. Both diets contained 0.42% P. On d 21, fecal grab samples were collected every 4 h for 48 h to represent every 2 h in a diurnal period. Neither DMI (26 kg/d) nor milk yield (38 kg/d) was affected (P > 0.1) by treatment. The concentration of P in the feces (0.70 and 0.71% DM for control and treatment cows, respectively) was not affected (P > 0.1) by supplemental hay nor did it change diurnally. Therefore, for dairy cows fed a TMR containing 0.42% P there was no diurnal change in the concentration of P in feces, and a forage top-dress did not affect the concentration of P in feces. Thus, fecal grab sampling appears to be a reasonable method to monitor P excretion. In conclusion, because of the variation in the concentration of P in fecal samples, the number of cows sampled within a group is more important than the time during the day that the samples are taken.