Digestibility of energy and nitrogen retention of diets with increasing proportions of co-product ingredients and formulated using the NE system

Abstract Text: Rising feed costs demand that our industry pursue strategies to lower the cost of production. One option is the adoption of the net energy system (NE), although many producers are hesitant to proceed without more definitive data. The objective of this experiment was to compare the ATTD of energy and the nitrogen retention (NR) of diets formulated using the NE system with increasing quantities of co-product ingredients. The 5 dietary treatments included a control corn-soy based control diet (CTL), a diet similar to the CTL but containing 6% each of corn DDGS, corn germ meal and wheat middlings with NE constant relative to CTL (18NE-CON), or allowed to decline (18NE-DEC), or similar diets but with 12% each of the same co-products and NE held constant (36NE-CON) or allowed to decline (36NE-DEC). Constant NE in the CON treatments was achieved by adding fat. Diets were formulated for both growing (40 to 70 kg; GP) and finishing (70 to 110 kg; FP) periods. Forty gilts (PIC 337 sires x C22 or C29; initial BW=38.5±0.4 kg) were randomly assigned to treatment, receiving fed and water ad-libitum throughout the experiment (69d). For the last 13 days of the GP and FP, pigs were transferred to metabolism crates, where two total urine and fecal collections (d4 to 6; d11 to 13) were performed. Data were analyzed using the MIXED procedure of SAS. In GP, ATTD of GE decreased in all co-product diets compared to the CTL (85.3 vs 79.9% for average of 18NE and 36NE; P<0.01). There were no differences between NE-CON and NE-DEC (80.5 vs 79.3%; P>0.05). In FP, ATTD of GE also decreased in co-product diets compared to the CTL (87.1 vs 82.6% for average of 18NE and 36NE; P<0.01). Unlike GP, the 18NE diets had a higher ATTD of GE compared to 36NE diets (P<0.05).  There were no differences between NE-CON and NE-DEC (82.7 vs 82.5%; P>0.05). NR declined on all co-product diets in the GP (40.6 vs. 35.5% for average of 18NE and 36NE; P=0.01) and tended to decline in the FP (35.0 vs. 30.2% for average of 18NE and 36NE; P=0.08). There were no differences between CON and DEC diets at 18NE or 36NE (P>0.05). In conclusion, diets containing up to 36% co-products and formulated using NE resulted in poorer NR than a simple corn-soybean meal control diet.

Keywords: Pigs, net energy, DDGS, wheat middlings, corn germ meal, nitrogen retention