Meta-analysis on the relationship among feeding characteristics, salivary and plasmatic cortisol levels, and performance of pregnant sows housed in different systems

This study was carried out to evaluate the relationship among the effects of housing systems, the nutritional composition of diets, and feeding program on performance and concentrations of salivary, and plasmatic cortisol in pregnant sows. The database was composed by 22 articles published from 1996 to 2010, totaling 170 treatments, and 1941 animals. Of the 22 studied articles 12 articles evaluated salivary cortisol, 9 evaluated plasmatic cortisol, and 1 article evaluated both salivary and plasmatic cortisol. The meta-analysis was performed by sequential analysis: graphical, correlation, and variance-covariance. Salivary cortisol was positively correlated (P<0.05) with feed composition, crude protein, total lysine intakes, and lysine level. Plasmatic cortisol was negatively correlated (P<0.01) with metabolizable energy level and positively correlated (P<0.01) with level and intake of crude protein. In groups housing on deep bedding, the salivary cortisol level was 10% higher (P<0.01) in relation to groups housing on concrete floor. The piglet's weight at birth decreased by 0.002 kg for each increase of a unit nMol L−1 in plasmatic cortisol (Y=1.6032−0.0002X) or salivary cortisol (Y=1.6026−0.0002X), measured in pregnant sows. The feeding (amount of feed per day) and the housing system (individual or groups) influence the levels of cortisol. Cortisol at high levels reduces the reproductive performance.