Title page for ETD etd-10282011-141717

Type of Document Dissertation
Author Jarrett, Jamie Pearl
URN etd-10282011-141717
Title Improving estimations of phosphorus bioavailability for lactating dairy cows
Degree PhD
Department Dairy Science
Advisory Committee
Advisor Name Title
Knowlton, Katharine F. Committee Chair
Akers, Robert Michael Committee Member
Hanigan, Mark D. Committee Member
Harrison, Joseph Committee Member
James, Robert E. Committee Member
Shang, Chao Committee Member
  • phytase
  • phosphorus
  • lactating dairy cattle
  • bioavailability
Date of Defense 2011-10-14
Availability unrestricted
Phosphorus (P) is an instrumental nutrient in numerous physiological processes, but can have detrimental environmental impact if fed in excess. Increased P intake in dairy cows leads to increased fecal excretion of P and a reduction in efficiency of use. Variability in P concentration or availability in feedstuffs can exacerbate P excretion. To investigate variability in P between and within feedstuffs, 170 feed samples (forages, concentrates, and by-products), were collected from across the U.S., classified by region fed, and analyzed for total P, inorganic P, and phytate. Forages contained a greater proportion of P in the inorganic form and less total P and phytate as compared to concentrates and by-products. The majority of total P (71.2, 81.8, and 81.9% of total P in forages, concentrates, and by-products, respectively) was associated with inorganic P and phytate. The enzyme phytase has been used successfully in swine and poultry nutrition, as a feed additive, to increase available P and reduce the need for supplemental inorganic P. An experiment was conducted to investigate the effect of phytase use and forage particle length, using a 2 x 2 factorial, on P availability in lactating dairy cows. Total P intake of the four diets was similar (P > 0.15). Total tract digestibility of total P tended (P < 0.10) to be reduced and total P excretion was increased (P < 0.05) with phytase supplementation. Milk fat yield, protein yield, 3.5% FCM, and ECM were increased (P < 0.05) with addition of exogenous phytase to the diet. This indicates that phytate may contain some anti-nutritional factors that reduce availability in other nutrients used for milk production. Variation in P compounds between feeds, and variation in P digestion and production performance with exogenous phytase suggests opportunity for improvement in prediction of P availability from feeds for lactating cows.
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