Return to oestrus caused by impaired feed intake; a case report

Introduction: Chronic physical stress and feed deprivation attribute to the risk of return to oestrus in mammals. Some of these factors have been shown in pigs experimentally, but case reports are rare. Data from electronic sow feeders (ESF) enable analysis on the association between feed intake and reproduction results. This case report describes the results of such analysis in a 1025 head sow farm which was experiencing a slight increased return to oestrus (8.8%) and a lower farrowing rate (86.5%) in 2014 compared to Dutch average figures. Return to oestrus peaked in gilts (20.4%) with a median interval between insemination and return to oestrus of 33 d (range 19 - > 60 d) leading to a probable diagnosis of early embryonic death as a cause of return to oestrus in gilts. Materials and Methods: Risk factors for chronic stress, such as feeding, housing, and management were thoroughly evaluated. Feed content, feed intake and reproduction data of 4 week groups (n= 220 sows) were analysed for associations with return to oestrus. Impaired feed intake was defined as at least two days with more than 70% rest feed in the first 14 days after introduction in the group housing. Results: Gestating sows were housed in 4 dynamic groups of 200 sows with 4 electronic sow feeders per group and straw bedding in the resting area. One group was used for parity 0 and 1 sows (p0 &p1). Whereas analysis of feed content showed adequate nutrient levels, intake data showed that 82% of p0 and 27% of p1 had more than 70% rest feed at least twice in the first two weeks after introduction in the group housing in contrast to 5.7% in p≥1 sows. 11/43 p0 and 3/44 p1 returned to oestrus. None of p0 without rest feed returned to oestrus. Cox proportional hazard analysis, contrasting impaired feed intake (Y/N) for p0 and p1 sows to the p>1 sows, showed a hazard ratio of 2.8-5.9 for return to oestrus in the impaired feed intake group. Analysis of ESF gilt training showed several flaws. Multiple stressors were found attributing to deprived learning. Firstly, gilts were regrouped and moved thrice after arrival on the farm. Aerial ammonia was 40 ppm and gilt-human interaction was inadequate. Most importantly, in the training area a through with ad lib feed was provided behind the training ESF. Gilts were thus conditioned to transit through the ESF to the through, instead of learning to eat in the ESF. Conclusion: This case report shows that combined analysis of data on feed intake and reproduction can be of additional value in the field and clearly pointed to the impact of improper training of gilts to eat from a ESF. L.Verhulst, I. Siemons, T. Sleegers and B. Goesten are acknowledged for their help.