Copper hydroxychloride improves gain to feed ratio in pigs, but this is not due to improved true total tract digestibility of acid hydrolyzed ether extract

Two experiments were conducted to test the hypothesis that copper (Cu) from Cu hydroxychloride improves gain to feed ratio (G:F) when fed to pigs by increasing apparent total tract digestibility (ATTD) of fat. In experiment 1, 144 pigs (15.40 ± 2.39 kg) were allotted to 6 treatments with 2 pigs per pen and 12 replicate pens per diet. Pigs were fed diets with increasing concentrations of extracted fat by adding 20, 40, or 60 g/kg choice white grease (CWG) to a diet based on corn, soybean meal (SBM), and distillers dried grains with solubles (DDGS), which contained no CWG. Two additional diets were formulated by adding 150 mg/kg of Cu from Cu hydroxychloride to the diet without added CWG and to the diet with 20 g/kg added CWG. Diets were fed for 4 weeks. Results indicated that supplementation of diets with either CWG or Cu hydroxychloride improved (P < 0.05) G:F of pigs, and the improvement obtained by Cu hydroxychloride supplementation was similar to the improvement in G:F obtained by adding 28–38 g/kg CWG to the diets. In experiment 2, 64 pigs (18.22 ± 1.80 kg) were housed individually in metabolism crates and randomly allotted to 8 diets with 8 replicate pigs per diet. Two basal diets based on corn, SBM, corn bran, cornstarch, and casein were formulated. The only difference between the 2 diets was that one diet contained no Cu hydroxychloride, whereas the other diet contained 150 mg/kg of Cu from Cu hydroxychloride. Six additional diets were formulated by adding 150, 300, or 450 g/kg DDGS to both basal diets at the expense of cornstarch and corn bran. Feces were collected using the marker-to-marker approach with 5-day adaptation and 4-day collection periods. Supplementation of Cu hydroxychloride to diets improved (P < 0.05) the ATTD of acid hydrolyzed ether extract (AEE), but did not affect ATTD of dry matter or gross energy (GE). Supplementation of Cu hydroxychloride to diets also reduced (P < 0.05) total tract endogenous loss of fat, but did not affect true total tract digestibility of AEE. This indicates that the increased G:F of pigs that was observed in experiment 1 as a result of Cu supplementation to diets was not due to improved ATTD of GE, but may be a result of Cu influencing post absorptive lipid metabolism. In conclusion, supplementation of Cu from Cu hydroxychloride to diets improved G:F in pigs, which may be due to effects of Cu on post-absorptive metabolism of energy and fat.