Date Full Report Received


Date Abstract Report Received


Background: With ever more strict regulations and market-driven bans on the use of individual gestation stalls, pork producers are considering to build new barns to group-house or transition from gestation stalls to group housing for pregnant sows. Sows in group housing usually require more floor space to maintain productivity and welfare compared with sows kept in individual gestation stalls. However, providing additional floor space for group-housed sows will reduce output from a given known footprint and will potentially reduce profitability. Producers are interested in group housing sows using the least possible space that does not compromise welfare of sows so that sow inventory and total output from the barn can be maintained. Objectives of this project were: 1). To determine the minimal square footage needed to successfully house sows in pens with electronic sow feeders (ESF); 2). To evaluate the utility of housing sows in pens with lower space allowance after their social hierarchy is established, to determine the efficient use of space and simultaneously maintain welfare and performance of sows; 3). To investigate effects of space allowance on performance, health, stress, and behavior of gestating sows in an ESF system; 4). To evaluate an innovative method of monitoring postural behavior of group-housed sows automatically using accelerometers.
Procedures: The project was conducted at the Southern Research and Outreach Center of the University of Minnesota in Waseca, MN between Feb. 2015 and Oct. 2016. Pregnant sows (n = 928, parity = 1 to 10) from 20 breeding batches were used. All sows were group-housed during gestation in pens equipped with an Electronic Sow Feeder (ESF). The ESF controlled individual feed intake of sows by means of a RFID (Radio-Frequency Identification) ear tag. Gestating sows were managed as a static group in each pen. Floor space allowances studied were: 22 ft2, 20 ft2, 18 ft2, 16 ft2 per sow, and 16 ft2 per sow with more space (22 ft2) during the first week of mixing (22/16 ft2). The floor space allowance treatments were achieved by adjusting pen size (range = 858 ft2 to 948 ft2) and group size (range = 42 to 51 sows). Each floor space allowance was tested in four pens over a period of 18 months. Sows were moved to ESF pens after being diagnosed pregnant at 5 weeks after mating. Sows remained in their ESF pens until day 109 of gestation when moved to individual farrowing stalls. Sows weaned their litters at about 18 days after farrowing. Sows that were rebred within one week after weaning a litter were considered to have completed the study. To achieve Objective 1 to 3, performance in gestation pens (body weight, back fat thickness, and body condition at entering and leaving ESF pens, daily feed intake, the number of days that the sow did not eat or failed to consume allotment), total days in gestation, farrowing rates, and lactation performance (litter size and weight farrowed and weaned, pre-weaning mortality, and ADFI during lactation), days in lactation, and wean-to-estrus interval after weaning their subsequent litters were measured for all sows. Welfare indicators, including skin lesions, the number of wounds, prevalence of lameness, and fighting among sows immediately after mixing, 2 days and 7 days after mixing were monitored for all sows. Salivary samples were collected for cortisol analysis from 8 focal sows each pen (balanced for parity) before moving into ESF pens, 2 days after mixing in ESF pens, and before moving to farrowing crates. Postural behaviors (lying lateral, lying sternum, standing, and sitting) were measured in all pens through live observations during week 3 and week 9 after sows were moved into ESF pens. Live observations consisted of scan-sampling all sows in a pen at 5-min intervals for 4 hours during the observation days (2 hours in the morning and 2 hours in the afternoon). To achieve Objective 4, accelerometers (HOBO Pendant G Acceleration Data loggers, Onset Computer Corporation, Bourne, MA) were fitted on a front leg and a rear leg of 8 focal sows in each pen during the same periods that live observations were conducted. Sow activities were recorded at 10-sec intervals for 3 consecutive days. Postural behaviors were calculated using the model generated in a validation trial. To validate accelerometers for detecting postural behaviors in pigs, an animal trial was conducted at the West Central Research and Outreach Center of the University of Minnesota in Morris, MN. Twelve pens of 8 pigs weaned at 4 weeks of age were used. In each pen, 4 focal pigs were selected randomly for behavioral monitoring which occurred at 5 week and 7 week of age. Each focal pig was fitted with a digital accelerometer (Onset Pendant G. Data Logger) on the rear leg, which recorded instant acceleration in 3-dimensions at 10 sec intervals for 24 hours. During the same period, behaviors of focal pigs were recorded continuously using digital cameras. Video-recordings were viewed to register postural behaviors that focal pigs were performing continuously for 2-min. Acceleration data series corresponding to each behavior were extracted. Data were analyzed to determine correct classification of postural behaviors using accelerometers.

Objective 1: Floor space allowance did not affect body weight, back fat thickness, condition scores, or feed intake at any time point measured during the study. No differences were detected in farrowing rates (95%, 92%, 94%, 94% and 95% for 16 ft2, 18 ft2, 20 ft2, 22 ft2, and 22/16 ft2, respectively), completion rates (83%, 79%, 80%, 86%, and 86%), live litter size farrowed (12.5, 12.7, 12.2, 12.3, and 12.5 pigs), litter size weaned (10.4, 10.5, 10.2, 10.2, and 10.6 pigs), litter weight farrowed and weaned, or wean-to-estrus interval among treatment groups. No differences were observed in aggression among sows (total duration of fighting, frequency of fights, and mean duration of each fight) and cortisol concentrations at any time point measured among treatment groups. Skin lesion scores for the body and vulva 2 days after mixing and before farrowing were similar across treatment groups. Prevalence of lameness 2 days after mixing was higher (Chi-square = 21.1; P = 0.01) for sows allowed 22/16 ft2 (9.5%) and 22 ft2 (4.2%) than sows allowed 20 ft2 (1.8%), 18 ft2 (2.9%), and 16 ft2 (1.5%), which may be associated with fighting to establish a dominance hierarchy during mixing in pens with larger open areas. No difference was observed in prevalence of lameness before farrowing among treatment groups. Floor space treatments did not affect postural behaviors at week 3 and week 9 in ESF pens. Sows spent most their time lying lateral (67 to 76% of total observation time across treatment groups), and lying sternum (16% to 24%), and less time on standing (2% to 4%) and sitting (< 1%). As gestation progresses, sows spent more time lying lateral and less time lying sternum. Collectively, these results suggest that floor space allowance of 16 ft2 per sow supports acceptable reproductive performance and welfare of gestating sows group-housed under conditions of the current study.
Objective 2: No difference was observed in any variables measured between sows that allowed 16 ft2 and sows that allowed 22/16 ft2 floor space. Providing extra space during mixing did not benefit the welfare or performance of sows under conditions of the current study.
Objective 3: Increasing floor space allowance from 16 ft2 to 22 ft2 did not affect the welfare or performance of sows. In general, there were no interactions between floor space allowance and sow parity category (parity 1 and parity 2, parity 3 and parity 4, parity 5 and parity 6, and parity 7 to parity 10) for variables measured, which suggests that sows, both young and old, responded to floor space treatments in a similar way. Providing extra space for the entire gestation period in the range tested did not benefit sows under conditions of the current study.
Objective 4: Accelerometers were validated for monitoring the posture of lying lateral and the posture of standing in pigs, with a correct classification rate of 93% for both postures in the current study. Accelerometers had difficulties to classify the posture of lying sternum in pig, with a correct classification rate of only 54%. The posture of lying lateral was estimated for sows in group-housing systems using accelerometer data, which showed a pattern similar to the results obtained from live observations. However, using accelerometers to detect postural behaviors in loose-housed sows presented challenges to data recording and processing.