Selection of an amino acid-deficient or -enriched diet by piglets under different sanitary conditions

Sub-optimal sanitary conditions resulting from poor hygiene practices alter amino acid (AA) metabolism of pigs, thereby changing their quantitative requirements. Pigs can select a diet that meets their AA requirements over an AA-deficient one when given the choice, suggesting potential for self-supplementation of AA in conditions that affect AA requirements. The present study investigated whether the self-supplementation of AA to compensate for the provision of an AA-deficient diet in a choice-feeding setting differs for piglets kept under high or low sanitary conditions. To this end, an experiment (2 × 2 factorial design) was performed with 60 weaned female piglets (TN70 × Tempo) (two piglets per pen). Piglets were kept under high (HSC) or low (LSC) sanitary conditions and were offered either a diet deficient in eight indispensable AA (IAA) (LP^-) (No choice) or the choice between the LP^- and a diet enriched with eight IAA (LP⁺) (Choice) for 19 days. Average daily feed intake (ADFI) and average daily gain (ADG) were recorded, and blood samples were taken to determine immune parameters. Piglets under LSC had 22 and 38% higher blood leukocyte and monocyte counts (P < 0.01 for both), respectively, and a 129% higher haptoglobin concentration in serum (P < 0.05) than HSC piglets. Moreover, neutrophil (+53%) and eosinophil (+43%) counts were increased in LSC pigs (both P < 0.001). Low sanitary conditions piglets had 31, 44, and 21% lower ADFI, ADG, and gain-to-feed ratio, respectively, than HSC piglets during the experiment (P < 0.01), while no differences between No choice and Choice treatments on these parameters were observed. Both LSC and HSC choice piglets ingested more of the LP^- than of the LP⁺ diet (P < 0.001). The course of the consumption of the LP⁺ diet in time differed between the two sanitary conditions (P < 0.01 for the interaction SC × Period): the percentage of LP⁺ consumed out of the total feed intake from the start to the end of the experiment doubled (from 6.5 to 13.2%) for HSC piglets, while it decreased from 10.6 to 1.4% for LSC piglets. Low sanitary conditions, while decreasing performance and activating the immune system, did not increase the preference for an AA-enriched diet. Thus, offering piglets the choice to self-select between an AA-deficient diet and one enriched with AA above the assumed requirement did neither restore growth performance nor affect immune status when kept under low sanitary conditions.