Faecal inflammatory biomarkers as non-invasive indicators of feed intake status in weaned piglets

Early weaning in piglets commonly leads to a postweaning (PW) fasting period, compromising intestinal integrity and triggering inflammation, overall affecting welfare and growth. Despite the well-documented consequences of fasting, no feasible and non-invasive method exists to monitor feeding patterns in postweaned piglets. Therefore, this study aimed to evaluate the use of faecal inflammatory biomarkers-calprotectin (fCal), lipocalin-2 (LCN-2), myeloperoxidase (MPO), and adenosine deaminase (ADA)-to detect whether an animal is eating or not by correlating fasting with its presence in faeces. The trial involved 623 weaned piglets (21 days) which were weighed at days 0, 3 and 10 PW. A blue-coloured creep-feed was provided before and after weaning to qualitatively trace feed consumption via rectal swabs. Piglets were assessed for feeding status at weaning and on day 3 PW. Additionally, 120 animals were selected to monitor feed status daily over the first 4 days PW. Animals were classified into three categories: creep-feed eaters (CFE), began feed intake preweaning and maintained it PW; PW eaters (PWE), started consuming feed PW; and non-eaters (NE), which did not consume any feed. Out of the 120 piglets, faecal samples were obtained from 77 piglets: CFE (n = 19 sampled from days 0-3), PWE (n = 7 on day 1, n = 14 on day 2, n = 33 on day 3), and NE (n = 30 on day 0, n = 28 on day 1, n = 27 on day 2, n = 25 on day 3). Among all piglets, 4.5% were classified as CFE, 69.5% as PWE, and 26% as NE. On average, CFE gained 44 g/day more than PWE, and 100 g/day more than NE in the first 10 days of PW (P < 0.001). The biomarkers fCal, LCN-2, and MPO differed by eater category (P ≤ 0.014), while ADA increased over time (P = 0.001) without differences between categories. Calprotectin and LCN-2 were higher in NE than CFE, correlating with reduced growth (r ≤ -0.29, P ≤ 0.044). Conversely, MPO was higher in CFE than NE (P < 0.001), with no growth association. Calprotectin showed strong discriminatory power between CFE and NE, with an area under the curve of 0.86, sensitivity of 86%, and specificity of 69%. Calprotectin and LCN-2 increased with fasting and correlated negatively with growth, highlighting their utility as biomarkers of low feed intake-related inflammation, with fCal being the most sensitive. Myeloperoxidase and ADA showed no feeding-related associations.