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The value of recycled phosphorous from pig droppings in the diet composition

Mineral-rich products derived from animal manure are often recycled through their use as fertilizer, primarily for their contribution to nitrogen and phosphorous. Another potential way to use nutrients from animal manure is through combustion to generate energy, leaving a sterile inorganic ash product that can be recycled back into animal feed. Previous work done at North Carolina State University has shown that ash from poultry litter and solids from pig manure and pig mortalities can serve as a digestible phosphorous source in pigs’ diets.

We have conducted a study to assess more closely the bioavailability of phosphorous in poultry litter ash and pig lake sludge. Lake pig sludge is a nutrient-rich residue that settles to the bottom of anaerobic pig lakes. It is rich in phosphorous, but also contains relatively high levels of zinc and copper.

For the study, we used 56 buggy hybrids, with an average weight of 77 pounds. They were individually housed and fed daily for three times their maintenance requirements. The feed was given twice daily at 8 AM and 4 PM and the pigs had unlimited access to water. Food treatments consisted of a passive diet that was deficient in phosphorous (40% of proposed requirement from NRC, 2012) and passive control regimens with additional phosphorus of 0.075% or 0.150% from either monosodium phosphate, turkey litter ash, or dried pig lake sludge. .

Monosodium phosphate was chosen as the standard with the reported phosphorous availability value of 100%. The phosphorous bioavailability of TLA and SLS can then be directly calculated and compared to this criterion. TLA used in this study was analyzed to contain 8.31% calcium, 3.98% phosphorous and 0.70% sodium, while SLS contains 5.81% calcium, 4.31% phosphorous and 0.12% sodium. These values ​​were used in the formulation of the experimental meals. Thus, the diets were balanced in proportion to the experimental design, maintaining a constant calcium-phosphorous ratio of 1.4 to 1, and using construction sand as a filler to maintain stoichiometric incorporation of all other components across the diets.

The 28-day diets were fed the entirety and growth rates of pigs were determined, as shown in Figure 1. Phosphorous addition increased the average daily gain of all phosphorous sources, but especially when phosphorus was supplied by MSP, as expected. This indicates that phosphorous in TLA and SLS was less bioavailable than phosphorous from MSP. The slope of the MSP in Figure 1 was 0.558 indicating that for each additional unit of phosphorous, the average daily gain increased by 0.558 kg per day. The slopes of TLA and SLS were 0.327 and 0.363, respectively. The ratio of the slopes relative to the slope obtained for MSP represents the relative bioavailability of phosphorous (assuming that the bioavailability of phosphorous for MSP is 100%). These data indicate a phosphorous bioavailability of 58.6% for TLA and 65.1 for SLS.

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Figure 1. Regression analysis of mean daily gain as a function of phosphorous supplementation from monosodium phosphate (MSP), turkey litter ash (TLA) or dried pig lake sludge (SLS).

We also collected third metacarpal bones from all pigs at the end of the 28-day study. Bone length was measured with digital calipers before bone strength was assessed using a three-point flexion test with 5 cm between the supports and a 250 kg load cell. The peak breaking strength was defined as the maximum supported load before failure.

Bone strength is often the most sensitive factor in assessing calcium and phosphorous requirements. As can be seen from Figure 2, the additional increase of phosphorous increased the bone fracture strength of all phosphorous sources. The response was greater when phosphorous was added from MSP as indicated by the larger slope of the line at 116.3, compared to the slope of 85.7 for TLA and 78.0 for SLS. Thus, the relative bioavailability calculated using peak bone fracture was 73.8% for TLA and 67.1% for SLS.

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Figure 2. Regression analysis of maximum bone fracture strength as a function of phosphorous supplementation from monosodium phosphate (MSP), turkey litter ash (TLA), or dried pig lake sludge (SLS).

This study evaluated the bioavailability of phosphorous from turkey litter ash and dried pig sludge with monosodium phosphate, which was used as a high-phosphorous control. Data show that the bioavailability of phosphorous from turkey litter ash and dried pig lake sludge is about 60 to 70% relative to monosodium phosphate. Thus, these recycled waste products can serve as potentially valuable alternative sources of phosphorous for pigs.

Source: Cooper McAuley and Eric van Heugten, who take full responsibility for the information provided, and own the information in full. Informa Business Media and all its affiliates are not responsible for any of the content contained in this information asset.

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