Submitted to: Canadian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2006
Publication Date: 6/1/2006
Citation: Thacker, P.A., Rossnagel, B.G., Raboy, V. 2006. The effects of phytase supplementation on nutrient digestibility, plasma parameters, performance and carcass traits of pigs fed diets based on low-phytate barley fed without inorganic phosphorus. Canadian Journal of Animal Science 86: 245-254 Interpretive Summary: Most of the phosphorus in grains and legumes is found as a compound called phytic acid. Non-ruminant animals such as poultry, swine and fish, as well as humans, do not digest phytic acid well. In addition, dietary phytic acid binds tightly to calcium and other mineral nutrients. As a result, when non-ruminants consume grain and legume-based diets, they excrete most of the phosphorus consumed, and in addition, the dietary phytic acid has a pronounced negative impact on calcium nutrition, and mineral nutrition in general. Furthermore, dietary phytic acid may negatively impact utilization of a diet's energy-containing compounds and other nutrients such as proteins. In this study growing pigs were fed a normal barley, or one of two different low phytic acid barleys that contain 50% or 70% less phytic acid than normal barley. In addition, each diet was formulated with or without a supplemental enzyme that breaks down phytic acid, called “phytase”. Reducing dietary phytic acid and increasing dietary available phosphorus using either the simple plant genetics and breeding made possible by low phytic acid genes, or via the addition of phytase supplement, increased the absorption of phosphorus from the barley and decreased the amount of phosphorus in the animal waste. Thus either using low-phytate crops or phytase supplements can improve the nutritional value of grains in terms of phosphorus, a nutrient important to animal growth. This can also result in reduced levels of phosphorus in animal waste, helping to reduce the impact of animal production on the environment.
Technical Abstract: A total of 80 crossbred pigs (25.5 + 2.6 kg) were assigned to one of eight dietary treatments. A positive control, based on Harrington barley, was formulated to meet requirements for total phosphorus. Three experimental diets (low in total phosphorus) were formulated based on either Harrington barley (0.28% phytate phosphorus) or the low phytate genotypes LP422 (0.14% phytate phosphorus) and LP 635 (0.09% phytate phosphorus). The four diets were fed with and without 1000 FTU/kg phytase. Calcium and phosphorus digestibility were significantly higher (P<0.05) as a result of supplementation with phytase. For the barley diets formulated without dicalcium phosphate, calcium digestibility averaged 69.6, 73.3 and 72.2% while phosphorus digestibility averaged 36.5, 50.5 and 57.7% for pigs fed the Harrington, LP 422 and LP 635 diets, respectively. The addition of phytase to the diet consistently reduced the percentage of phosphorus excreted in feces and fecal phosphorus excretion declined as the level of phytate in the barley declined. The addition of phytase tended to improve weight gain (P<0.10) and significantly improved feed conversion (P<0.05). For pigs fed the barley diets formulated without dicalcium phosphate, daily gain averaged 0.90, 0.99 and 1.01 kg/day while feed conversion averaged 2.70, 2.39 and 2.38 for the Harrington, LP 422 and LP 635 diets, respectively. The overall results of this experiment indicate that the performance of pigs fed diets containing low-phytate barley formulated without a source of inorganic phosphorus is at least equal to that of pigs fed diets containing normal-phytate barley and inorganic phosphorus. In addition, the increased availability of organic phosphorus reduced the amount of phosphorus excreted thus reducing the amount of phosphorus that can potentially pollute the environment.