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.