Protein degradability and intestinal digestibility of blood meals: comparison of two processing methods

Crude protein degradability (nylon bag technique) and intestinal digestibility (mobile bag procedure) of blood dried by two processes: batch (BBM) (temperature: 100–160°C; drying time: 5–7 h) or batch modified (BMBM) (vacuum applied: 0.2 atm; temperature: 70°C; drying time: 1–2 h) were estimated. Blood meals obtained from industrial plants (four samples per process) averaging 92 (BBM) and 86% (BMBM) CP on DM, were evaluated using three Holstein dairy cows fed alfalfa hay (10 kg per day). Two degradability (in sacco technique) and one intestinal (mobile bag technique) assays were performed. Particle size was characterized by dry sieving (arithmetic mean, mean particle size and percent sample retained in 50μ mesh), and particle washout dynamics was studied. Physical characterization of particles suggest BBM had higher number of particles scaping initially from bags while, as incubation time increased, BBM and BMBM washouts from bags were similar. In both assays, no time effect (P>0.3) on nitrogen disappearing from rumen was observed suggesting N losses occurred at, or before, first incubation time. N degradability of BMBM was higher (P<0.05) than BBM (25 versus 14% and 28 versus 22% assays 1 and 2, respectively). Differences in degradability between assays could result from increased particle losses from bags in assay 2 when meals were ground before incubation, since BBM and BMBM zero — time incubation values in assay 1 and 2 were similar (γ=0.95). N soluble fraction was estimated incubating meals samples in buffer solution, as N losses from bags not incubated in rumen (To), and as To values corrected by proportion of particles lost through sieve 50 μ (Top). Estimates of N rapidly degraded in rumen were similar for buffer procedure (3 and 4%, BBM and BMBM) and Top (4 and 6%, BBM and BMBM) and lower than To (17 and 21%, BBM and BMBM). Potentially rumen degradable fractions (N degradability — Top) were 19 and 24% for BBM and BMBM, representing 85% of rumen degradable protein. There were not detected differences in intestinal digestibility of undegraded N (BBM: 20%; BMBM: 27%) between processes (P>0.7). Variations in meals N intestinal digestibility were registered within each process (BBM: 14–33%; BMBM: 15–60%). Variation in N ruminal dynamics and intestinal protein digestibility within and between processes may be attributed to lack of uniformity in the industrial procedures, particularly protein coagulation before drying. Results indicate blood meals quality may be variable and vacuum application reducing exposure of blood to heat may increase protein availability. Estimates of rapidly degraded N by sample incubation in buffer and zero time correction by <50μ particles were similar, indicating convenience to sieve blood meals before rumen incubation.