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Assessing essential amino acid availability from microbial and rumen undegraded protein in lactating dairy cows.

X. Huang

Events

06-24-2020

Abstract:

351
Assessing essential amino acid availability from microbial and rumen undegraded protein in lactating dairy cows.
X. Huang*1, P. Yoder1,2, L. Campos1, E. Huang1, M. Hanigan1. 1Virginia Tech Blacksburg, VA, 2Perdue AgriBusiness LLC Salisbury, MD.

The objective of this study was to assess a stable isotope technique for determination of essential AA availability from microbial protein in response to starch and rumen degraded protein. The study was designed as a 2 � 2 factorial arrangement with a repeated 4 � 4 Latin square design. Factors were high and low rumen degraded protein, and high and low starch. Twelve lactating cows were blocked into 3 groups according to days in milk, and randomly assigned to the 4 treatment sequences. Each period was 14 d in length with 10 d of adaption followed by 4 d of ruminal infusions of 15N labeled ammonium sulfate. On the last day of each period, a 13C-labeled AA mixture was infused into the jugular vein over a 6 h period to assess total AA entry. Rumen, blood, and urine samples were collected during the infusions. Ruminal microbes and blood samples were assessed for AA enrichment. Total plasma AA absorption rates were derived for each essential AA from the plasma, 13C-AA enrichment. Essential AA absorption from microbial protein was calculated from total AA absorption based on 15N enrichment in blood and rumen microbes. Microbial AA absorption rates derived from the isotope dilution model were greater for the high rumen degraded protein diets and unaffected by starch level, except for Met, which decreased with high starch. Microbial protein outflow estimated from purine derivatives increased with rumen degraded protein and was not significantly affected by starch, which was consistent with estimates from the isotope dilution model. Total AA absorption rates derived from the isotope dilution model were similar to estimates from CNCPS (v6.5), but a lower proportion of absorbed AA was derived from microbial protein for the former method. Assuming 7.6% loss during first pass through the splanchnic tissues, the average essential AA digestibility for microbial AA was 82%, which varied across AA and by treatment. The new method has the advantage of quantifying the essential AA availability for individual EAA from rumen undegraded protein and microbial protein.

Keywords: dairy cow, microbial protein, amino acid availability.