Title page for ETD etd-08162006-105715


Type of Document Master's Thesis
Author Yang, Tzu-Hsuan
Author's Email Address tzu727@vt.edu
URN etd-08162006-105715
Title Effects of diet on phosphorus digestion in dairy cattle
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Knowlton, Katharine F. Committee Chair
Akers, Robert Michael Committee Member
Berry, Duane F. Committee Member
McGilliard, Michael L. Committee Member
Shang, Chao Committee Member
Keywords
  • dairy cow
  • non-fiber carbohydrate
  • phosphorus digestion
  • phytic acid
  • beet pulp
Date of Defense 2006-08-08
Availability unrestricted
Abstract
Two studies were conducted to evaluate the effects of diet on phosphorus (P) digestion in dairy cattle. The objective of the first study was to evaluate the effects of forage and non-fiber carbohydrate (NFC) content on total P (TP) and inositol phosphates-P (IPs-P) digestion. Samples of feed, duodenal digesta and feces from a previously conducted study were analyzed for TP and IPs-P. In this study, eight lactating Holstein cows were fed diets containing either 60 or 35% forage and either 30 or 40% NFC in a 2 × 2 factorial with replicated 4 × 4 Latin square design. Dietary TP content (% DM) was 0.35, 0.36, 0.36, 0.36 and dietary IPs-P content (%DM) was 0.08, 0.13, 0.06, 0.11 for diets with forage: NFC ratio 35:30, 35:40, 60:30, and 60:40, respectively. Increasing dietary forage content decreased IPs-P and TP intake, fecal TP excretion, and total tract IPs-P digestibility (72.4 vs. 61.4%). Fecal IPs-P excretion tended to decrease as increasing forage content. Duodenal IPs-P and TP flow and apparent TP digestibility were unaffected by forage content. Increasing dietary NFC content increased IPs-P and TP intake, duodenal IPs-P flow, fecal IPs-P excretion, total tract IPs-P digestibility (61.4 vs. 72.4%), and apparent TP digestibility (32.8 vs. 41.6%). Dietary forage and NFC content affected IPs-P and TP digestion. The second study was to evaluate the effects of increasing dietary beet pulp (BP) content to replace high moisture corn (HMC) on ruminal and post-ruminal digestion of TP and IPs-P. Eight lactating Holstein cows were fed diets containing 0, 6.1, 12.1 or 24.3% BP in a replicated 4 × 4 Latin square design. Samples of rumen contents, duodenal digesta, and feces from this previously conducted study were analyzed for TP and IPs-P content. Linear and quadratic effects of BP content were analyzed using Proc Mixed of SAS. Dietary TP and IPs-P content were reduced linearly with increasing BP (0.59, 0.58, 0.57, 0.56% TP and 0.15, 0.14, 0.13, 0.11% IPs-P). Intake, ruminal content, and rumen pool size of TP decreased with increasing BP content. Digestion of TP and duodenal flow and fecal excretion of IPs-P and TP were not affected. With increasing dietary BP content, IPs-P intake was reduced, ruminal IPs-P pool size was reduced, and rumen turnover time (h) of IPs-P was increased. Apparent ruminal IPs-P digestibility (36.5, 31.8, 24.6, 13.6 %) and apparent total tract IPs-P digestibility (85.3, 82.7, 82.1, 79.1%) decreased linearly with increasing BP. Fecal excretion of IPs-P averaged 5.2 g/d. Replacing HMC with BP reduced digestion of IPs-P. The majority of IPs-P disappearance occurred post-ruminally. In conclusion, dietary BP, forage, and NFC content affected IPs-P digestion in dairy cows.
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