Title page for ETD etd-08262002-122603

Type of Document Master's Thesis
Author Guyton, Autumn Deanne
URN etd-08262002-122603
Title Starch Digestion and Phosphorus Excretion in Lactating Dairy Cows
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Knowlton, Katharine F. Committee Chair
Pearson, Ronald E. Committee Member
Polan, Carl E. Committee Member
  • phytase activity
  • Phosphorus and nitrogen excretion
  • starch digestion
Date of Defense 2002-08-08
Availability unrestricted
The effects of starch and phosphorus (P) source on P partitioning and ruminal phytase activity were evaluated in eight lactating cows (113 DIM). Four cows were ruminaly cannulated. Cows were randomly assigned to treatments in a duplicated 4x4 Latin square with four, 18-d periods. Diets included dry ground corn (DG) or steam flaked corn (SF), with a no supplemental P (low P diet; 0.34% P) or supplemental purified phytic acid (PA; 0.45% P) to provide additional P from an organic source. Total collection of milk, urine, feces, and feed were sampled each period, while rumen fluid was sampled on d 18. Excretion of feces, urine, P, and N was lower in cows fed SF than in cows fed DG. Milk yield was unaffected by diet despite a lower DMI by cows fed SF. Cows fed SF tended to have a higher feed efficiency and lower milk urea nitrogen (MUN) concentration than cows fed DG. Rumen pH was unaffected by diet, but milk fat content was lower for cows fed SF. Milk yield, DMI, and feed efficiency were not affected by PA. Cows fed PA had increased P intake and excretion, but a lower milk P as a percentage of intake compared with cows fed the low P diet. An interaction of starch source and P source was observed for ruminal phytase activity. Altering dietary sources of starch and P offers opportunity to improve P availability and reduce manure nutrient excretion.

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