The effect of immunization against gonadotropin-releasing factor in market gilts: Meta-analyses of parameters relevant for pig producers, pork packers and retailers/consumers

The vaccine against gonadotropin releasing factor (GnRF), Improvac®, has recently emerged as an option for rearing market gilts up to heavier harvest weights. Improvac's® temporary suppression of the ovarian function and gonadal hormones results in greater feed intake and better welfare from avoidance of sexual behavioral problems. Based on 22 published articles, our meta-analysis has quantified the effect of immunizing gilts against GnRF on parameters relevant for pig producers, pork packers and retailers/consumers. The meta-analyses included growth performance and final harvest parameters, general carcass traits and yield of valuable meat, meat and fat quality parameters. Primary analyses considered studies without ractopamine, subgroup and additional analyses assessed the impact of co-variates. From the perspective of pig producers, primary analyses showed that immunized (IM) gilts have significantly (P < 0.001) increased average daily gain (+45.1 g/day) and daily feed intake (+0.19 kg/day), higher final live weight (+4.0 kg) and more backfat (+2.8 mm). From the perspective of the pork packers, IM gilts have heavier carcasses (+3.2 kg; P < 0.001), whereas dressing percentage is similar. IM gilts are less lean (-1.5% units; P < 0.001) and have 0.21% units more intramuscular fat (P = 0.001). The yield of ham, shoulder, and loin is similar, whereas the yield of belly is significantly higher (+0.28 kg; P < 0.001). There are no differences in meat quality parameters (color, pH₂₄, and drip loss) between IM gilts and untreated gilts, whereas a lower iodine value in IM gilts indicates an improved fat quality. Further subgroup and additional analyses confirmed the validity of our meta-analysis.