The objective was to investigate the effects of dietary unsaturated:saturated fat ratio (U:S) and the fatty acid ratio of linoleic acid:linolenic acid (n6:n3) on growth performance of grow-finish pigs. A total of 240 pigs with initial body weight (BW) 54.4±5.5kg were randomly assigned to a high ( >1.8; HUS) or low ( < 1.0; LUS) U:S ratio with a high (20:1), moderate (12:1) or low (4:1) n6:n3 in a 3×2 factorial design (n=10). Diets were fed across three phases and balanced for energy and linoleic acid. Pigs were housed 4 pigs per pen and separated by sex. Data were analyzed as repeated measures using SAS (9.4) with pen as the experimental unit and U:S ratio, n6:n3 ratio, sex, and their interactions as fixed effects. Initial BW was fit as a covariate. Within each phase, there were no differences in BW, daily gain (ADG), feed intake (ADFI) or feed efficiency (G:F) for U:S, n6:n3, or their interaction (P>0.10). For the overall period, there was a U:S×n6:n3 interaction for ADG (P<0.05) with pigs receiving LUS×12:1 (1.19kg/d) having increased ADG compared to pigs receiving HUS×12:1 (1.12kg/d). There was no effect of sex (P>0.10) for G:F within each phase; however, overall, gilts had improved G:F compared to barrows (P < 0.05). Compared to HUS, gilts receiving LUS had higher ADFI overall (P<0.05; 2.84 vs. 2.70kg), which translated into improved G:F for HUS gilts (P < 0.05; 0.40 vs 0.39). Overall, gilts receiving the 20:1 diet tended to have improved G:F compared to 12:1 (P < 0.10; 0.40 vs 0.39).
The dietary U:S ratio impacted overall ADG of pigs fed the 12:1 ratio when averaged across sex; however, there was no significant sex × U:S × n6:n3 interaction. A low U:S ratio can also increase feed intake of gilts; however, this did not result in improved ADG.