Mixing gilts in early pregnancy does not affect embryo survival

There is general acceptance that mixing sows during the first 3 weeks of gestation is detrimental to embryo development and survival. However, there is a paucity of data describing the influence of group housing and remixing during the first 14 days of gestation on pregnancy outcomes. Using 96 purebred maternal (Large White)/terminal (Duroc) line gilts, the current study determined the effects of regrouping, and the timing of regrouping, during the pre-implantation period on embryo mortality. The study was conducted in 2 blocks, with 12 gilts allocated to each of 4 treatments in each block. At 175 days of age, the combination of PG600 and 20 min of daily physical boar contact was used to stimulate puberty, with boar contact resuming 12 days after first detection of oestrus and gilts receiving two artificial inseminations (AIs), 24 h apart, at their second oestrus. After their first AI gilts were allocated to one of four treatment groups (n = 12 gilts/treatment). Gilts in one treatment group were housed individually in stalls (STALL). The remaining gilts continued to be housed in their pre-AI groups and were either not remixed (NOMIX), or remixed to form new groups on day 3/4 (RMIXD3/4) or day 8/9 (RMIXD8/9) of gestation (day 0 = day of first detection of second oestrus and first insemination). Group-housed gilts were housed in groups of 6, with a space allowance of 2.4 m2/gilt. All gilts were fed once a day (2.2 kg/gilt). Reproductive tracts were collected on day 26.6 ± 0.13 of gestation, and the number of corpora lutea (CL) and viable embryos counted. Pregnancy rate was similar across all treatments, averaging 94.5% across the four treatment groups. The number of embryos present on day 26 of gestation was unaffected by housing treatments (P > 0.05); gilts in the STALL, NOMIX, RMIXD3/4 and RMIXD8/9 groups possessed 13.2 ± 0.67, 12.9 ± 0.66, 14.1 ± 0.46 and 13.8 ± 0.57 embryos, respectively. Similarly, embryo survival rates were 0.91 ± 0.04, 0.85 ± 0.04, 0.91 ± 0.02 and 0.87 ± 0.05 for the STALL, NOMIX, RMIXD3.4 and RMIXD8/9 groups, respectively (P > 0.05). In conclusion, the current data indicate that individually housing gilts immediately after their first AI does not improve embryo survival. There also appear to be no adverse effects on embryo development or survival when group-housed, mated gilts are remixed during the first 10 days of gestation.