Serum creatinine is a poor marker of a predicted change in muscle mass in lactating sows.

Serum creatinine (SCr) in humans has proven to be a reliable biomarker of body protein breakdown and/or muscle mass change. This study set out to investigate the potential of SCr to indicate a loss in sow muscle mass over lactation, validated against 3 methyl histidine (3MH) and blood urea nitrogen (BUN), markers of dietary and/or body protein breakdown. A total of 40 sows were allocated to four treatment groups aimed to induce body weight changes by restrictively feeding sows using a stepwise percentage reduction model. Data were pooled and reallocated into three groups representing the 25 , 50 and 75 percentiles based on body weight change over lactation in the range -22.3 to -4.1% (treatment 25), -4.0 to 6.2% (Treatment 50), and 6.3-15.2% (Treatment 75). Indirect measures for the prediction of protein (3MH, BUN) or fat change (caliper, P2) were taken on entry into the farrowing house, day 5 of lactation, and at weaning. Serum was collected on these days, and SCr, 3MH and BUN were analysed. Piglet weaning weight and average daily feed intake did not differ between treatments (p > .05). There were no changes (p > .05) in indirect measures of body composition (sow caliper score, P2) and analytes (SCr, 3MH, BUN) over lactation. By day 20, those sows in treatment 25 had higher (p < .05) 3MH concentrations whilst changes from day 5 to 20 were not different (p > .05) and did not correlate with SCr change (p > .05) but were highly correlated to BUN change (R = 0.691, p < .001). The data suggested that concentrations of SCr and BUN may have been the result of dietary and/or body protein breakdown and/or changes in muscle mass. In the current testing conditions, SCr was not a reliable marker of changes in muscle mass.