35 Viral disease alters feed preferences in grower pigs

Abstract Porcine Reproductive and Respiratory Syndrome (PRRS) virus reduces feed intake and growth rates and increases mortality risk in pigs. During this disease state, it is unclear if macronutrient and feed preferences change to support the immune response. Our objective was to evaluate how diet composition impacts feeding preferences during PRRS. In Exp. 1, pigs were offered a choice between a corn-soybean meal (CON) and a CON + 3.75% glucose and fructose high sugar (HS) diet. In Exp. 2, pigs were offered both CON and CON plus functional amino acids (10–20% increase in methionine, threonine, and tryptophan; FAA) diets. In Exp. 3, pigs were presented with CON, a high-protein diet (28% increase in CP; HCP), or a high-fat diet (20% increased metabolizable energy; ME) diets. Each experiment contained six pens of mixed-sex pigs (40 ± 5.5 kg) that were randomly allotted to pens (Exp. 1 and 2 contained three pigs/pen, Exp. 3 contained four pigs/pen). On day post inoculation (dpi) 0, one pig/pen was inoculated intramuscularly with a live PRRS virus. Body weights and feed disappearance were recorded weekly (-1 week post-inoculation [wpi] and at 1, 2, and 3 wpi) to calculate ADG, ADFI, and feed preference. Feed preference was expressed as the percentage of each tested diet relative to total feed intake. Data were analyzed using a linear mixed model with the fixed effect of wpi and wpi by diet. As expected, ADFI decreased (P< 0.001) in Exp. 1 (2.17, 2.27, 1.74 and 2.16 kg/d), Exp. 2 (2.10, 2.06, 1.62 and 1.92 kg/d), and Exp. 3 (1.64, 1.93, 1.53, and 1.96 kg/d) over wpi. In Exp. 1, ADG and G:F did not differ by wpi. Over the challenge period, ADG decreased by up to 50% (P< 0.05) in Exp. 2 and 3. In Exp. 2, G:F tended to decrease during 2 wpi compared to -1 and 1 wpi, recovering by 3 wpi (P=0.08), and did not differ for Exp. 3 (P=0.114). In Exp. 1, HS diets were preferred over CON in wpi -1 and 1 wpi (84% vs. 16%, respectively); however, by wpi 2 and 3, HS preference decreased to 55% compared to 45% for CON (P=0.015). Across all wpi, HS diets were preferred over CON (69% vs. 31%, P=0.001). In Exp. 2, no diet by wpi was reported. However, overall, the CON was preferred over FAA (63% and 37%, respectively, P=0.02). No wpi by diet interaction was reported in Exp. 3 (P=0.17). However, overall, the HCP and ME were preferred over CON (42, 36, and 22%, respectively, P=0.003). In conclusion, pigs prefer diets containing natural sweeteners, higher crude protein, or energy during peak PRRS. Further research is needed to determine if this is driven by olfactory or gustatory factors.

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