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Does heat stress alter the pig's response to dietary fat source, as it relates to carcass iodine value?
Heat stress results in major losses to the pork industry through reduced growth performance and possibly carcass fat quality. The objective was to investigate the effect of heat stress on the pig’s response to dietary fat in terms of growth performance and pork fat quality over a 35 d finishing period. A total of 96 barrows (PIC 337 × C22/29) with an initial BW of 100.4 ± 1.2 kg were randomly allotted to 1 of 9 treatments arranged as a 3 × 3 factorial: [TN (thermonetural: constant 24°C; ad libitum access to feed), PFTN (pair-fed thermoneutral: constant 24°C; limit-fed based on previous HS daily feed intake), or HS (heat stress: cyclical 28°C nighttime, 33°C d 0 to 7, 33.5°C d 7 to 14, 34°C d 14 to 21, 34.5°C d 21 to 28, 35°C d 28 to 35 daytime; ab libitum access to feed)] and diet [a corn-soybean meal based diet with 0% added fat, 3% added tallow (iodine value (IV) = 41.8), or 3% added corn oil (IV = 123.0)]. Pigs were individually housed to track intake and undertake jowl fat biopsies. Data were analyzed using PROC MIXED with environment and dietary treatment as fixed effects, and replicate (2 replicates of 48 barrows) as a random effect. Rectal temperature (HS = 39.0, TN = 38.1, PFTN = 38.2°C) and respiration rates (HS = 78, TN = 36, PFTN = 34 bpm) increased due to HS (P < 0.001). HS decreased ADFI (27.8%; P < 0.001). ADG (HS = 0.72, TN = 1.03, PFTN = 0.78 kg/d; P < 0.001), and G:F (HS = 0.290, TN = 0.301, PFTN = 0.319; P = 0.006) also reduced by HS. G:F but not ADG or ADFI tended to be influenced by dietary treatment (0% added fat = 0.292, 3% tallow = 0.303, 3% corn oil = 0.314 g/100 g; P ≤ 0.073). Exposure to HS did not impact IV at market (HS = 69.2, TN = 69.3, PFTN = 69.8 g/100 g; P = 0.624). Carcass IV increased with increasing degree of unsaturation of the diet fat (0% added fat = 68.5, tallow = 68.2, corn oil = 71.5 g/100 g; P < 0.001). There was no interaction between HS and diet (P ≥ 0.191) on carcass IV. In conclusion, HS impaired growth performance but not carcass IV or the response to dietary fat. IV was affected by dietary fat source.
Keywords: Heat stress, fat, iodine value