Year of Publication

2005

Document Type

Dissertation

College

Agriculture

Department

Animal Science

First Advisor

Merlin D. Lindemann

Abstract

For economical and ecological reasons, efficiency and profitability ofswine production relies heavily on the way pigs utilize key nutrients such as P,which is considered a potential pollutant of water ecosystems. Although cerealgrains and oilseed meals contain enough P to fulfill the biological needs of pigs,most of this P is tightly bound as phytate. As pigs do not have enough phytase(PHY) to cleave P from phytate, it is excreted in the feces. To prevent adeficiency, diets have traditionally been supplemented with highly availableinorganic sources of P. Today, an environmentally-friendly alternative is tosupplement diets with PHY.Growth promoting antibiotics are also used to enhance the utilization ofdietary components such as energy and N. It has been suggested that theantibiotic virginiamycin (VIR) could also improve phytate-P utilization by pigs.Eight experiments evaluated the effects of VIR and/or PHY amendmentson digestibility, retention, excretion, growth, bone characteristics, meat traits, andileal microflora populations of growing pigs fed corn–soybean meal (SBM) diets(seven experiments) or corn-SBM-rice bran diets (one experiment). Additionally,a comparison between two digestibility procedures was conducted for two of theexperiments.On average, VIR improved P digestibility and total P excretion by 5.0%,and P retention as a percent of absorption by 1.0%. Phytase amendmentsimproved P digestibility between 14 and 27%, and P retention (as a % ofabsorption) between 0.7 and 2.5%. In the growth trial, VIR supplementation wasassociated with numerical differences favoring bone mineralization and ilealphytate-utilizing bacteria populations. These observations demonstrate additionalresearch is warranted with this antibiotic under conditions of higher stress andbacterial load in the environment.According to the comparisons between digestibility methods, a single grabfecal collection was not reliable. Further, a cumulative grab collection for fivedays was not as good an option as the total collection method.It is concluded that VIR does improve P utilization in pigs fed corn-SBMdiets not supplemented with inorganic P. Similar effects, but of greatermagnitude, were confirmed for PHY-amended diets with either normal or highlevels of phytate P.

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