A meta-analysis to identify animal and management factors influencing gestating sow efficiency. 
A meta-analysis on the effects of management and animal-based factors on the reproductive efficiency of gestating sows can provide information on single-factor and interaction effects that may not have been detected in individual studies.  This study analyzed the effects of such factors on the number of piglets born alive per litter (BA), piglet birth weight (BiW) and weaning weight (WW), and number of piglets born alive per kilogram of sow feed intake during gestation (BA/FI).  A total of 51 papers and 7 data sources were identified for the meta-analysis, out of which 23 papers and 5 sets of production data were useable (a total of 121 treatments).  The information gathered included the dependent variables as well as information regarding animal, management, and feed characteristics.  While a number of factors were individually significant, the multivariate models identified significant effects only of 1) floor type (P=0.003), sow BW at the end of gestation (P=0.002), and housing (stalls vs. loose; P=0.004) on BA; as floor type and housing were confounded, they were included in 2 separate models.  The BA was higher on solid (12.1) in comparison to partly slatted (11.4) and fully slatted floors (10.2); 2) sow gestation environment (P=0.017) and gestation feed allowance (P=0.046) on BiW, with BiW of pigs higher for sows kept outdoors rather than indoors (1.75 versus 1.49 kg); 3) parity number (P=0.003) and feed intake during gestation (P=0.017) on WW; in addition there was an interaction between parity number×feed ME and parity number×feed CP content of feed during gestation on WW, with the positive effects of feed ME and CP contents seen during early rather than later parities; and 4) floor type (P=0.019) and feed crude fiber (P=0.003) for BA/FI with a greater number for those kept on solid floors (5.11) versus partially and fully slatted floors (4.07 and 4.05).  The meta-analysis confirmed the significant effect of several well-known factors on the efficiency of gestating sows and, importantly, the interactions between these factors.  In addition, the effects of some less established factors were noted, such as floor type.  The results may contribute towards the improvement of efficiency of gestating sow systems by better understanding of the various factors that influence this.