Abstract: Three ruminally cannulated Holstein cows in late lactation were used in a complete randomized experiment to compare runimal and rectal sampling sites for estimating digesta passage kinetics in the rumen of lactating Holstein cows. The experimental diets were consisted of chopped corn stalk and concentrate, for which the ratio of forage to concentrate was 55:45. Chromium-mordanted hay (Cr-NDF) was used as particulate marker and Cobalt-Ethylenediamine Tetraacetic Acid (Co-EDTA) as a liquid-phase marker and they were administered by one-time infusion through rumen cannulae to determine passage rates of the particulate (kp) and liquid (kl) phases from the rumen and rectum, respectively. Both rumen contents and faecal samples were collected to analyze Cr and Co concentration. Then, the fractional digesta passage rates were calculated by linear regression of natural log transformed Cr and Co concentrations in ruminal content or faeces. The results were showed as follows: fractional passage rates of solid and liquid digesta measured directly in the rumen were 0.0411/h and 0.112/h whereas they were 0.0387/h and 0.0573/h when calculated from the faecal Cr and Co concentration curves. The correlation equation between the fractional passage rates of liquid digesta from the rumen and rectum is y(r) = 2.0141x(f) – 0.00399, R2 = 0.9966, p = 0.037 [y(r): Passage rate of liquid digesta measured directly in the rumen, x(f): Passage rate of liquid digesta calculated from the faecal Co concentration curve]. The correlation equation between the fractional passage rates of solid digesta from the rumen and rectum is y(r) = 0.3535 x(f) + 0.02743, R2 = 0.8326, p = 0.27 [y(r): Passage rate of solid digesta measured directly in the rumen, x(f): Passage rate of solid digesta calculated from the faecal Cr concentration curve]. Results suggest that measuring marker concentration curves in rectum always results in a considerable underestimation of the digesta passage rates from the rumen, however, the digesta passage rates from the rumen can be predicted by faecal marker concentration curves derived from the rectal sampling to some extent especially for liquid passage rate of digesta from the rumen in dairy cows.
T.Z. Zhao, H.Y. Li, B.L. Shi and S.M. Yan, 2013. Comparison of Ruminal and Rectal Sampling Sites for Estimating Digesta Passage Kinetics in Rumen of Holstein Cows Fed Corn Stalk-Based Diets. Journal of Animal and Veterinary Advances, 12: 959-964.