Abstract #T203

# T203
Effects of drying procedures of milk, urine, and fecal samples on nitrogen losses and its effects on nitrogen secretion and excretion in dairy cows.
D. L. Morris*1, A. W. Tebbe1, W. P. Weiss1, C. Lee1, 1Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio.

Drying of milk, urine or feces for nitrogen (N) analysis can result in N losses; therefore, this study examined the effect of drying method on N concentration in those samples. Twelve lactating cows assigned to 2 groups were fed 4 treatment diets for 21 d with total collection of milk, urine, and feces on the last 4 d. Daily subsamples of feces, urine, and milk were composited by cow and analyzed for N by Kjeldahl or with an elemental analyzer (EA). Fresh feces, milk, and urine were directly applied to Kjeldahl (no drying). For EA analysis, milk and urine were pipetted into tin cups, lyophilized for 8 h or oven-dried at 55°C for 1 h and then applied to EA; fecal samples were lyophilized for 120 h or oven-dried at 55°C for 72 h and analyzed for total N in EA. All data were analyzed using the MIXED procedure of SAS with fixed effects of dietary treatment, method, and treatment by method and the random effects of group and group by treatment. No interaction of dietary treatment and method was observed. Because Kjeldahl analysis occurred without drying samples, this was used as a reference to compare dried samples to. Results of N concentration, secretion, and excretion from different drying methods are shown in Table 1. Milk, urine, and fecal N concentrations by EA after lyophilizing or oven drying did not differ. However, fecal N concentration decreased about 5% when analyzed with EA compared with Kjeldahl. In addition, N concentrations of milk obtained by EA was 10% greater than Kjeldahl, indicating that Kjeldahl likely under predicts milk N concentration and therefore secretion. Table 1. Nitrogen concentration and partitioning calculated from different drying methods
WetLyophilizingOven dryingKj vs. EAEA
Milk N, g/L4.985.455.550.2640.040.70
Milk N, g/d200.6218.0223.08.310.010.57
Urine N, g/L6.576.536.740.2450.800.48
Urine N, g/d213.1212.0218.815.190.720.36
Fecal N, % of DM2.942.782.800.1070.0030.78
Fecal N, g/d240.3227.3228.16.740.0540.92
1Kj vs. EA, Kjeldahl vs. EA (lyophilizing and oven drying); EA = lyophilizing vs. oven drying.

Key Words: nitrogen determination, drying method