Potential to Improve Fiber Digestion in the Rumen

  • Author / Creator
    Griffith, Candace L
  • Ruminants have the capacity to utilize fibrous plant materials as substrates to provide energy for maintenance and growth. However, digestion of poor quality forage is incomplete in ruminants and varies among individual animals. Consequently, two studies were conducted in an attempt to elucidate differences among cattle, in terms of their abilities to digest forages. The effect of attempting to modify their microbiomes through inoculation with bison rumen contents, on forage digestibility was also examined. The first experiment was conducted to determine whether ruminal digestibility of forage fiber by cattle could be increased by partially replacing rumen contents with bison rumen contents. Our secondary objective was to investigate differences in ruminal digestion kinetics among individual heifers, and differences in their response to inoculation with bison rumen contents. An in situ digestibility study was performed using 16 ruminally-cannulated heifers and four fiber sources: barley straw, canola straw, alfalfa hay, and timothy hay. Bags were incubated in duplicate, before and after inoculation, for 0, 4, 8, 12, 24, 48, 96, and 120 h and digestion kinetics were determined as washout fraction (a), potentially degradable fraction (b), rate of degradation (kd), lag (L) and total potentially degradable fraction (a+b). No mean effect of inoculation with bison rumen contents was seen on effective ruminal degradability (ERD) for any feeds incubated (P > 0.10). However, a small decrease (P > 0.05) in kd and a+b fraction of barley straw was observed as a result of the inoculation, likely because cattle were already well adapted to a barley straw diet, while bison were not. A mean increase (P < 0.05) in a+b, with a concomitant decrease in kd of alfalfa hay was observed. It was found that digestion kinetics varied among heifers both before and after inoculation, and each heifer responded differently to inoculation with bison rumen contents. Using the in situ digestibility kinetics measured in the first experiment, rumen inoculum was obtained from two heifers with the fastest kd of barley straw NDF, and two heifers with the slowest kd of barley straw NDF. Conventional barley straw, and barley straw treated by ammonia fiber expansion (AFEX) were used to examine differences between inoculum types. Two Rusitec apparatuses, with 8 fermenters in each, were used in a 4 × 4 Latin square design with 4 treatments and 4 fermenters per treatment. No effects of kd or rumen inoculum were observed for digestibility of untreated barley straw. However, inoculum from heifers with a fast kd digested AFEX straw to a greater extent (P < 0.05) than did inoculum from heifers with a slow kd. These differences were believed to be due differences in the nature of the rumen microbiome between inoculum donors. Together, these studies investigate individual variability among cattle in their ability to digest forages. They highlight how differences in rumen microbiome may impact fiber digestion in the rumen. Further investigation is needed to understand the exact microbial differences that are responsible for this variability in digestibility, and the potential to enhance the microbiome of cattle that exhibit less efficient ruminal fiber digestion.

  • Subjects / Keywords
  • Graduation date
    Spring 2017
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.