Strategic Use of Dietary Copper During the Growing-finishing Phase and Its Effects on Pig Growth Performance

Abstract Pharmacological levels of copper (Cu) in pig production improve growth. However, concerns have increased due to environmental concerns, and some countries have regulated the levels of certain minerals in swine diets. An alternative approach is to develop strategies for utilizing minerals like zinc or copper more efficiently in swine nutrition. The industry commonly utilizes phytase, which may increase mineral availability, and feeds trace minerals above the NRC recommendations. The objective of this study was to evaluate the impact of feeding two levels of added copper, industry (16.5 ppm) and NRC (3.0 ppm), with and without phytase on growth performance, carcass traits, and blood parameters during the growing–finishing phase in pigs previously fed diets containing 150 ppm copper. A total of 437 PIC 1050 × Compart Duroc pigs (46.6 ± 6.0 kg initial BW) were used in a day-0 study at the South Dakota State University Swine Research Unit. Pigs were housed in slatted pens with ad libitum access to feed and water and were fed four-phase diets (d0–15, d15–28, d28–43, d43–62). At d0, pigs were individually weighed and assigned by BW to one of four dietary treatments in a 2 × 2 factorial arrangement: two Cu levels (3.0 or 16.5 ppm) and phytase (0 or 0.3% of the diet). Each treatment had 19 replications with 6 pigs per pen. Body weight was recorded at the start and end of each phase. Blood samples were collected at d0 and d62, centrifuged, and stored at –80 °C for later analysis. Carcass traits, including backfat via ultrasound at d62, were measured on 212 pigs (53 per treatment) at slaughter. Liver and Muscle were collected from 10 animals per treatment for copper status analyses. Data were analyzed using PROC GLIMMIX (SAS). From day 0-15, a significant Cu x Phytase interaction was observed for ADG and feed efficiency, where pigs fed 16.5 ppm Cu without phytase and pigs fed 3 ppm Cu with Phytase had higher ADG (p = 0.007). No significant interactions were observed in the latter phases or overall. Overall, pigs fed 16.5 ppm Cu had greater weight gain (p = 0.009). Carcass traits were unaffected, although there was directional effect for increased back fat with Cu, aligned with the ultrasound results for greater backfat in pigs fed 16.5 ppm Cu (p = 0.006). Plasma Cu status did not differ among treatments, but serum Cu tended to be lower (p = 0.093) in pigs fed phytase. Also, copper status did not differ along the treatments. While the industry level of copper improved growth, pigs can be fed 3 ppm Cu in the latter phases with minimal impact on performance, as feed conversion was unaffected and ADG decreased only slightly.