Effect of low-phytate barley or phytase supplementation to a barley-soybean meal diet on phosphorus retention and excretion by grower pigs

¹ Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5
² Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5; Instituto de Ciencias Agricolas, Universidad Autónoma de Baja California, Mexicali, México 21100
³ Instituto de Ciencias Agricolas, Universidad Autónoma de Baja California, Mexicali, México 21100
⁴ Field Crop Development Centre, Lacombe, AB, Canada T4L IW8

^* To whom correspondence should be addressed. E-mail: ruurd.zijlstra{at}ualberta.ca.

	Abstract

Two studies were conducted to determine the effect of diets containing low-phytate barley or supplemented with phytase on P balance and excretion in grower pigs. In Exp. 1, 8 32-kg barrows were assigned to a repeated 4 x 4 Latin square design and fed 4 diets that contained 96% barley: normal-phytate hulled barley (HB), low-phytate hulled barley (LPHB), normal-phytate hull-less barley (HLB), and low-phytate hull-less barley (LPHLB). The barley cultivars contained 0.16, 0.05, 0.24, and 0.03% phytate, respectively. Inorganic P (iP) was added to HB and HLB to meet the 1998 National Research Council recommendation of available P (aP; 0.23%), while LPHB and LPHLB contained sufficient aP. The diets were fed at 2.5 times the maintenance requirement for ME. The apparent total tract digestibilities (ATTD) of P did not differ between the hulled and hull-less barley diets, but P retention (%) and excretion were greater in pigs fed the hull-less barley diets (P < 0.05). The ATTD of P was greater and P excretion was 35% lower in pigs fed the low-phytate than normal-phytate diets (P < 0.001). The amount of P retained (g/d) was higher (P < 0.001) in pigs fed low-phytate barley, reflecting an ATTD of P of 65 and 49% for low-phytate and normal phytate barley, respectively (P < 0.001). In Exp. 2, 8 21-kg barrows were assigned to a repeated 4 x 4 Latin square design and fed 4 diets based on barley and soybean meal (SBM): HB-SBM, HB-SBM + iP, HB-SBM + phytase, and LPHB-SBM. The HB-SBM and HB-SBM + phytase were deficient in aP while HB-SBM + iP and LPHB-SBM were adequate. The feeding regimen was similar as in Exp. 1. Adding iP to the HB-SBM diet did not affect the ATTD but increased the amount of P retained (g/d) and excreted (P < 0.001). The ATTD and amount of P retained (g/d) did not differ among pigs fed the HB-SBM + iP, HB-SBM + phytase, and LPHB-SBM diets. However, pigs fed the HB-SBM + phytase and LPHB-SBM diets excreted 32 and 29 % less P, respectively, than pigs fed the HB-SBM + iP diet (P < 0.05), confirming that low phytate barley is as effective as supplemental phytase in improving P digestibility and utilization and decreasing P excretion in grower pigs.

Key Words: barley, low-phytate, nutrient excretion, phytase, phosphorus, pig