Effect of Frequency of Boar Exposure on Estrus and Ovulation in Weaned Sows as Determined by Real-Time Ultrasound.

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1 Effect of Frequency of Boar Exposure on Estrus and Ovulation in Weaned Sows as Determined by Real-Time Ultrasound. Robert V. Knox, Kilby Willenburg, Gina Miller, Sandra Rodriguez-Zas Department of Animal Sciences University of Illinois Introduction Reproductive performance in swine is most related to inseminations occurring near the time of ovulation. This is due to the time-span for normal fertilization of eggs being limited by both the egg after the occurrence of ovulation (<12 h) and the sperm after insemination (<24 h). Therefore, the number of eggs that are fertilized, the percentage of normal embryos, the resulting pregnancy rates (Hunter and Dzuik, 1968, Soede et al., 1995), farrowing rates (Nissen et al., 1997), and litter size (Kemp and Soede, 1996; Rozeboom et al., 1996) are all related to time of insemination relative to ovulation. Insemination within 12 h before ovulation, appears to produce the most optimal pregnancy rates (>90%) and litter sizes ( , Kemp and Soede, 1996) but Nissen et al has observed that inseminations occurring from 28 h before to 4 h after ovulation result in high reproductive rates (Nissen et al., 1997). Unfortunately, the time of ovulation is difficult to predict since the only obvious marker for this event is the expression of standing estrus. Further, the time of ovulation varies between 24 to 60 h after onset of estrus (Soede et al., 1992). This high level of variation is important since insemination protocols are set from estrus, with inseminations typically occurring twice between 0 and 48 h. There appears to be a normal distribution for ovulation time after onset of estrus, with 20% of weaned sows ovulating by 24 h, 55% ovulating between 24 and 48 h, and 25% ovulating after 48 h (Knox et al., 1999a). It would appear then, that current insemination protocols may not fully account for the total variation in ovulation times within the breeding herd. This would help explain why average USA reproductive rates are less than optimal. This experiment was conducted to address whether estrous detection frequency could be used as a method to increase the frequency of fixed time inseminations that occur within 24 or 12 h prior to the time of ovulation in anticipation of early ( 24 h), expected ( 24 h and 48 h) and late times of ovulation ( 48 h). In commercial settings, a common industry practice employs a once daily estrous detection procedure with insemination targeted to occur at 0 h for the first service (estimated time relative to estrus is 0-24 h) and 24 h later for the second service (estimated time relative to estrus is h). Although this procedure can generate 79% farrowing rates, it cannot account for the variation in time of ovulation, since onset of estrus can be off by as much as 24 h. Even twice daily estrous detection procedures (0800 h and 1600 h) that rely on an 8 h working day, cannot compensate for this variation, since sows detected in estrus at 0800 h, may have already been in estrus for up to 16 h. Additionally, since approximately 70% of the females will show the first standing response between 6 p.m. and 6 a.m., large estimation errors result (±16 h) for onset of estrus, leading to inseminations that fail to occur within 24 h prior to ovulation. This experiment was designed to evaluate the effect of increasing frequency of boar exposure for accurately determining onset of estrus and time of ovulation in weaned sows. More frequent estrous detection was evaluated for its effect on percent of sows returning to estrus and 144

2 ovulating, interval from weaning to estrus, interval from estrus to ovulation, frequency of ovulation, and percent of inseminations occurring within 24 h prior to the time of ovulation. Materials and Methods The experiment was conducted in six replicates between January and August Sows were from parities 1 to 9 (average parity 3.9 ± 0.2), and represented commercial maternal-line genotypes, and both crossbred and purebred maternal and terminal lines from 3 different farms. Sows were weaned on average 18.2 ± 0.3 d after parturition (range: 14 to 30 days). Sows were randomly allotted to boar exposure frequency of once daily (1X, n = 63), twice daily every 12 h (2X, n = 61), or three times daily at 8 h intervals (3X, n = 62) by genotype, parity, and lactation length. Sows were weaned into gestation crates with boars housed in separate rooms or at least 40 feet away. Boar exposure was initiated at 1300 h 3 days after weaning with exposure to boars occurring in the alleyway at the front of the crate for approximately 2 to 5 minutes. Estrus was determined using the back-pressure test. Once standing estrus was observed, transrectal ultrasound was performed every 8 h to visualize the ovaries and determine the occurrence of ovulation. All sows were artificially inseminated twice with 3.0 billion sperm cells in long-term extender and used 4 days from collection. Sows in the 1X group were bred at 0 and 24 h, sows in the 2X group at 12 and 24 h, and sows in the 3X group at 16 and 32 h after first detected in estrus. Results The wean to estrus interval was not influenced frequency of boar exposure and averaged 4.5 days (Table 1, Figure 1). The percent of sows expressing estrus in 8 days (90-100%) was not influenced by treatment or month (Table 2). However, the percentage of sows ovulating tended to be influenced by treatment (P >.05) with 84.5% of 2X and 3X boar exposed sows ovulating compared to 98% of 1X exposed sows (Table 2). The wean to ovulation interval was not influenced by treatment and averaged 6.5 days (149.8 ± 5.1 h). Average largest follicle size at estrus was also not influenced by treatment or month and averaged 7.6 mm (Table 1). Length of estrus averaged 58.5 h and was influenced by treatment and also by month but there was no interaction (Figure 1). Estrus was longer (P <. 005) in the 3X exposure group compared to the 2X and the 1X exposure groups (Table 1). The shortest length of estrus (P <.05) occurred in the months of August, February and March (40 to 49 h), and the longest lengths in April and June (75 to 58 h, Figure 1). The estrus to ovulation interval was not influenced by treatment (Table 1) or month (Figure 1) and averaged 45 h. The occurrence of ovulation to the end of standing estrus was also influenced by month, but not by treatment (Table 1). The shortest interval from ovulation to end of estrus occurred in the February and March replicates (9 to 13 h), and intermediate intervals in late March and August (23 h) and longest intervals in April and June (44 to 33 h, Figure 1). More frequent boar exposure improved the percentage of 1 st and 2 nd inseminations occurring within 24 h before ovulation (Table 3). Conclusions The results of this experiment indicate that increasing frequency of boar exposure for weaned sows can improve the precision for timing inseminations and increase the frequency of 1 st and 2 nd services administered within 24 h before ovulation. Higher frequency of boar exposure does not influence wean to estrus, estrus to ovulation or wean to ovulation intervals but does increase 145

3 length of estrus and could indicate a tendency for lowered return to estrus and ovulation in certain seasons of the year. Season of the year appears to influence both the length of estrus the interval from ovulation to end of estrus. Taken as a whole, it is not clear whether the observed advantage in insemination timing will result in higher farrowing rates and litter sizes and that these will off set the cots associated with lowered estrus and ovulation rates and the extra labor for estrous detection. Lastly, it appears from our results that timing two inseminations to occur within 12 to 24 h before ovulation based off of weaning alone could prove beneficial since ovulation occurs at h plus or minus 5 h (145 to 155 h). Future experiments will investigate whether fixed time inseminations that occur at 138 and 150 h after weaning which allow time for sperm capacitation and sperm reservoirs to become established can produce good reproductive performance. References Hunter R. H. F., Dziuk P. Sperm penetration of pig eggs in relation to the timing of ovulation and insemination. J Reprod Fertil 1968; 15: Kemp B, Soede NM. Relationship of weaning-to-estrus interval to timing of ovulation and fertilization in sows. J Anim Sci 1996; 74: Knox, R.V., Lamberson, W. R. and Robb, J. 1999a. Factors influencing time of ovulation postweaned sows determined by trans-rectal ultrasound. Theriogenology 51:435 Nissen AK, Soede NM, Hyttel P, Schmidt M, D Hoore L. The influence of time of insemination relative to time of ovulation on farrowing frequency and litter size in sows, as investigated by ultrasonography. Theriogenology 1997; 47: Rozeboom KF, Troedsson MHT, Shurson GC, Hawton JD, Crabo BG. Late estrus or metestrus insemination after estrual inseminations decreases farrowing rate and litter size in swine. J Anim Sci 1996; 75: Soede NM, Noordhuizen JPTM, Kemp B. The duration of ovulation in pigs, studied by transrectal ultrasonography, is not related to early embryonic diversity. Theriogenology 1992; 38: Soede NM, Wetzels CCH, Zondag W, de Koning MAI, Kemp B. Effects of time of insemination relative to ovulation, as determined by ultrasonography, on fertilization rate and accessory sperm count in sows. J Reprod Fertil 1995; 104:

4 Table 1. Influence of Frequency of Boar Exposure on Wean to Estrus Interval (WEI), Estrus to Ovulation (EstOv), Wean to Ovulation (WOv), Length of Estrus (LEst), and Follicle Size at Estrus. Probability Boar Exposure Frequency Parameter Treatment Replicate 1X 2X 3X S.E. WEI (h) NS NS EstOv (h) NS NS WOv (h) NS NS LEst (h) OvEst (h) NS Follsz (mm) NS NS Table 2. Influence of Frequency of Boar Exposure Frequency on Percentage of Weaned Sows Expressing Estrus and Percent Ovulating in 8 Days. Parameter 1X 2X 3X P Estrus (%) NS Ovulation (%) NS 147

5 Table 3. Influence of Frequency of Boar Exposure Frequency on Percentage of 1 st and 2 nd Inseminations Occurring at Various Hour Intervals Before or after Ovulation in Weaned Sows. Boar Exposure Frequency 1X 2X 3X Interval 1 st (%) 2 nd (%) 1 st (%) 2 nd (%) 1 st (%) 2 nd (%) -72 h h h h h h h st A.I. within 24 h (%) 19.3 a 41.0 b 51.9 b 2 nd A.I. within 24 h (%) 70.8 a 72.5 a 74.9 b means in row with different superscripts differ, P <.05. Figure 1. Influence of Month on Wean to estrus (WEI), Wean to Ovulation (WOv), Onset of Estrus to Ovulation (EstOv), Ovulation to End of Estrus (OvEst), and Length of Estrus (LEst). Hours Jan Feb Mar Apr Jun Aug Month WEI Wov EstOv OvEst Lest 148