Publication history: Accepted - 20 June 2022; Published online - 4 July 2022Background: Diet evaluation and optimization is a slow and expensive process and it is not possible to do it at a
farm level. This study aimed to use the blood serum metabolite (BSM) and faecal volatile fatty acid (VFA) profles as
potential biomarkers to identify changes in protein, amino acid and energy dietary content in growing and fnishing
pig diets at farm level.
Results: Two studies were conducted. The frst study (S1) included 20 pens of 11 pigs (87.0±4.10 kg; 18 weeks old)
assigned to 5 diets: control (C1), high or low crude protein (HP1 and LP1, respectively), and high or low net energy
(HE1 and LE1, respectively). The second study (S2) included 28 pens of 11 pigs (41.3±2.60 kg; 12 weeks old) assigned
to 7 diets: control (C2), high or low crude protein (HP2 and LP2, respectively), high or low amino acid (HA2 and LA2,
respectively), and high or low net energy (HE2 and LE2, respectively). Pigs were followed for 10 (S1) and 20 (S2) days,
and blood and faecal samples were collected at 20 (S1) and 14 (S2) weeks of age. Data were analysed using gen‑
eral linear models and receiver operating characteristic curve analysis. Urea nitrogen showed the best results as a
biomarker. Urea nitrogen was higher in pigs fed high protein diets, HP1 (13.6±0.95 mg/dL) and HP2 (11.6±0.61),
compared to those fed low protein diets, LP1 (6.0±0.95) and LP2 (5.2±0.61; P<0.001), showing good discrimination
ability (Area under the curve (AUC)=98.4 and 100%, respectively). These diferences were not observed between
diets LA2 (6.5±0.61) and HA2 (8.7±0.61; P>0.05; AUC=71.9%), which were formulated based on the ideal protein
profle but with no excess of protein. Creatinine, triglycerides, branched-chain fatty acids, albumin, propionic acid, and
cholesterol showed diferences between at least 2 diets but only in one of the studies.
Conclusions: Urea nitrogen showed high accuracy to detect excess of crude protein in growing and fnishing pig
diets. Other biomarkers like BCFA showed promising results and need to be further studied.Jordi Camp Montoro was supported by the Teagasc Walsh Scholarship Scheme grant-in-aid project Introducing new feeding programs and facilities for Irish finishing pigs ref 0415. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript