Characterizing body temperature and activity changes at the onset of estrus in replacement gilts

Authors: Johnson, Jay; SHADE, KEVIN - Purdue University

Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2017
Publication Date: 3/4/2017
Citation: Johnson, J.S., Shade, K. 2017. Characterizing body temperature and activity changes at the onset of estrus in replacement gilts. Livestock Science. 199:22-24. doi.org/10.1016/j.livsci.2017.03.004.

Interpretive Summary: Breeding efficiency in replacement gilts (female pigs that have never been bred) may be improved by more effective methods of determining the onset of estrus. Estrus detection is one of the most critical components of a successful swine breeding program and standard detection methods and insemination timing often relies on animal caretaker observations. Familiarity with swine behavior is essential in this critical management skill and it is estimated that the overall labor input required is 30% for commercial facilities. Swine estrus signs include a swollen red vulva, riding behavior between pen mates, seeking a boar, standing in response to the presence of a boar, and standing in response to a back pressure test. Animal caretakers often use a boar to stimulate these behavioral signs. Unfortunately, in replacement gilts this can be labor intensive and require daily estrus checks as gilt cycling patterns are unpredictable and high variation is seen in the duration of estrus and ovulation timing. Furthermore, as the U.S. swine industry moves towards group-housing systems, the ability for animal caretakers to detect behavioral signs of estrus in individual pigs will likely become more difficult. Therefore, we performed a study to determine if a single device could remotely detect physiological and behavioral changes associated with the onset of estrus in replacement gilts. Based on previous research, we hypothesized that the onset of estrus would be accompanied by a reduction in body temperature and an increase in activity of replacement gilts. We determined that at the day of estrus, the body temperature of replacement gilts was reduced, and that activity was increased compared to baseline. In addition, these changes were linear with body temperature decreasing and activity increasing in the days leading to estrus. In summary, these data may be used to develop a tool for swine producers to detect estrus in replacement gilts, which will be increasingly important as the U.S. swine industry moves toward group-housing where manual detection of behavioral changes associated with estrus will likely become more difficult.

Technical Abstract: Accurate estrus detection can improve sow conception rates and increase swine production efficiency. Unfortunately, current estrus detection practices based on individual animal behavior may be inefficient due to large sow populations at commercial farms and the associated labor required. Therefore, the study objective was to characterize body temperature and activity changes in replacement gilts at the onset of estrus in order to provide data to develop a remote estrus detection system for commercial swine operations. Twelve replacement gilts (130.2 ± 1.9 kg BW) were administered altrenogest to synchronize estrus, and data loggers that detect vaginal temperature (TV) and quantify total activity 24 h/d in 5 min intervals were attached to blank sheep controlled internal drug release devices and inserted intra-vaginally for 7 d prior to expected estrus. Activity was quantified as counts per minute (cnt/min) using an internal accelerometer. During the 7 d of monitoring, gilts were checked for estrus twice daily (0800 and 1500 h) by two trained individuals. To standardize data, only the day of estrus detection (dE) and the three days prior (d-3, d-2, d-1, n = 4 total days) were used in the final analysis since gilts came into estrus on different days. Data were analyzed using the PROC MIXED procedure in SAS 9.4. Overall, TV was reduced (P < 0.01; 0.26°C) on dE compared to the previous three days; however, no differences were detected between d-3, d-2, and d-1. Activity was increased (P < 0.01; 37.8%) on dE compared to d-3 and d-2, but no differences were detected between dE and d-1. Vaginal temperature decreased linearly (P = 0.02; 0.08°C/d) from d-3 to dE and activity increased linearly (P < 0.01; 0.34 cnt/min/d) from d-3 to dE. In summary, TV was reduced and activity was increased at the onset of estrus.