S-1000 Regional Project
Animal Manure and Waste Utilization, Treatment and Nuisance Avoidance for a Sustainable Agriculture
2003 Station Reports

Reporting Scientist: Gary L. Cromwell – Department of Animal Sciences
Location: University of Kentucky, Lexington, KY.

Objectives:
1. To assess the effects of feeding diets containing low-phytate corn and low-phytate soybean meal without and with added phytase on phosphorus utilization and phosphorus excretion in pigs and chicks.
2. To determine accretion rates of phosphorus in whole body of pigs from 20 to 120 kg body weight in order to develop mathematical models to estimate phosphorus requirements and excretion.

Progress to date:
    Experiments with chicks and pigs have been conducted over the past several years with low-phytate corn containing the mutant lpa-1 gene and low-phytate, low-oligosaccharide soybean meal.  The low-phytate corn contained about half as much phytate phosphorus (0.10 vs 0.20%) and considerably more non-phytate (inorganic) phosphorus (0.18 vs 0.05%) than a near-isogenic normal corn.  The low-phytate soybean meal contained less phytate phosphorus (0.22 vs 0.48%) and more inorganic phosphorus (0.55 vs 0.22%) than soybean meal produced from near-isogenic soybeans. 

    Based on slope-ratio analysis of bone strength and ash, the bioavailability of phosphorus in low-phytate corn was three to four times greater than in normal corn for pigs (77 vs 22%) and chicks (50 vs 10%).  Similarly, the bioavailability of phosphorus in low-phytate soybean meal was more that twice as great as that of the phosphorus in normal soybean meal for pigs (49 vs 19%) and chicks (58 vs 28%). 

    Pigs fed diets containing low-phytate corn and low-phytate soybean meal with no added inorganic phosphorus had similar growth performance and bone mineralization as those fed normal corn and normal soybean meal with conventional levels of supplemental inorganic phosphorus. Pigs and chicks fed diets containing low-phytate corn and low-phytate soybean meal excreted approximately 50% less phosphorus in their manure than those fed normal corn and normal soybean meal. When phytase was included in combination with the low-phytate ingredients, phosphorus excretion was reduced by 70% in both pigs and chicks compared with those fed conventional diets.

    In general, the inclusion of phytase in low-phosphorus diets tended to increase the proportion of phosphorus excreted in urine as compared with feces, but the total excretion of soluble phosphorus was only slightly increased with phytase addition. Soluble phosphorus excretion was not consistently affected by feeding low-phytate corn or low-phytate soybean meal to either pigs or chicks.

    Two experiments have been completed to determine the phosphorus accretion in bone, hair, muscle and fat tissue of pigs serial slaughtered at eight weights ranging from 20 to 120 kg body weight. In addition, three balance experiments have been conducted with low phosphorus diets to estimate endogenous excretion and maintenance requirements for phosphorus at three body weights. From the data, we anticipated being able to develop mathematical models for estimating phosphorus requirements and phosphorus excretion of growing-finishing pigs based on amounts of nutrients needed for maintenance and tissue accretion rate.
   
Usefulness of findings:
    Improving the dietary phosphorus utilization by non-ruminant animals (swine and chickens), reduces the excretion of phosphorus in their manure, which has important environmental implications.

Planned work for 2003-2004.
    Assess the feeding of low-phytate grain and oilseed meals in combination with phytase on the amount and type of phosphorus (soluble and insoluble) excreted.
    Refine the estimates of phosphorus accretion in various tissues in order to develop a mathematical model to estimate phosphorus requirements and phosphorus excretion of pigs under varying dietary and environmental regimens.
Publications (1998-2003):

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