Effect of physical Versus fence-line boar exposure on synchronization of estrus following administration of a synthetic progestagen to mature gilts Jake Stewart, Suzanna Storms, Dr. Robert Knox Department of Animal Sciences, College of Agriculture, Consumer and Environmental Sciences University of Illinois Urbana-Champaign INTRODUCTION RESULTS Figure 2. Gilt replacement is essential to compensate for sow reproductive failure, sow performance and longevity problems. Annual gilt replacement rate often exceeds 50%. However, there are numerous environmental and management factors that can affect the efficiency of gilt entry into the breeding herd and their subsequent fertility. Estrus expression for both treatments was 100% within 10 days. Expression of estrus is shown in Figure 2. Gilts receiving PBE showed estrus on days 4-6 while those in FBE showed estrus on days 4-9. Synchrony of estrus is shown in Figure 3. Gilts in PBE showed an 78% synchrony within 48 h and 100% synchrony in 72 h compared to 50 and 60% for gilts receiving FBE, respectively. OBJECTIVES CONCLUSIONS The objective of this experiment was designed to test whether twice daily physical boar exposure (PBE) compared to once daily fence-line boar exposure (FBE) would improve expression and synchrony of estrus in mature gilts. Using PBE following Matrix would appear to be a cost effective method to improve synchrony of estrus in replacement gilts. This degree of synchrony would allow for smaller gilt pools and improve breeding group management. This preliminary study showed an effective method of boar exposure and should be repeated with more observations in a research and production setting. Figure 3. METHODS AND MATERIALS This project was performed at the University of Illinois Swine Research Center (SRC) in August–September 2013. Crossbred terminal line Genetiporc gilts (n=25) were selected at 170  2 d of age, verified for prepubertal status using trans-rectal ultrasound, and moved into gestation stalls (Figure 1). Gilts were treated with PG600 and exposed to a boar every 12 hours. Following d 6, all gilts that had expressed estrus were fed a synthetic progestagen (Matrix) for 14 consecutive days as a top dress on their daily feed. Following last Matrix® feeding (LMF), gilts (n=19) were moved into pens and randomly assigned to receive either FBE or PBE for 10 days. Gilts assigned to FBE were moved to a single pen (12.6 sq.ft./gilt) and exposed to a mature boar in an adjacent pen for 15 min. once each day. Gilts assigned to PBE (n=9) and moved into a pen (18.2 sq.ft./gilt) received physical boar stimulus for 15 minutes every 12 hours. PBE Pen (n=9) FBE Pen (n=10) Boar Pen Figure 1. BARN LAYOUT (arrows indicate boar movement). Building air flow Gestation stalls