Floor feeding over multiple drops does not increase feeding opportunities for submissive sows

Feeding sows from the floor is one of the simplest and cheapest method of feed delivery, but often results in high levels of aggression as sows compete for access to food. This may lead to subordinate sows sacrificing the opportunity to feed in an attempt to avoid receiving aggression. This study examined whether floor feeding sows their daily ration over multiple bouts per day creates more opportunities for subordinate sows to feed. Two-hundred pregnant gilts were mixed into pens of 10 (1.8 m²/gilt) within 7 days of insemination and floor fed four times per day (07:30, 09:00, 11:00, 15:00 h). The identity of gilts that were feeding (head down, rooting the ground/feed, chewing) was recorded, along with her location in the pen [on the cement area where feed was scattered (i.e. feeding area; F), directly under the feeder (i.e. high feed availability; HF), on the slats at the back of the pen (i.e. little or no feed availability; NF)], every 30 s for 20 min after each feed drop on days 2, 9 and 51 post-mixing. Gilts were also classified as dominant (D), subdominant (SD) or submissive (S), as described elsewhere. GLMM in conjunction with LSD tests were used to analyse the effects of gilt classification, day and feeding bout on the time gilts spent feeding in each location. Each model included a repeated effect of day and feeding bout within gilt, and pen nested within replicate as a random effect. Regardless of feeding drop (P > 0.05) or day (P > 0.05), D spent the most, and S the least, time feeding at the HF location. In feed drops 1, 2 and 4, the time SD spent HF was intermediate to S and D, but in drop 3 the time SD spent HF was comparable to S (classification × drop interaction P = 0.01). Irrespective of feed drop (P > 0.05), S gilts spent less time in the feeding area (P < 0.001), and more time in the NF location (P = 0.03), than D and SD, while the latter two did not differ. Feeding gilts over multiple drops does not increase feeding opportunities for subordinate sows. Regardless of feed drop or day, D gilts occupied the area of high feed availability and likely had the highest feed intake. That SD appear to adopt a strategy of feeding between and around the D gilts in areas of reduced feed availability. However, S gilts appear to be at greatest risk of low feed intake, which may result in reduced body condition and increased hunger and frustration. Further research is required to determine how the feed intake of subordinate sows can be increased in floor feeding systems, while also protecting these animals from aggression.