猪人工授精技术要点

１ 发情周期和排孵时间１．１ 母猪发情周期，一般为１８～２１天，排卵在发情症状开始后２５～３６小时，持续期为１０～１５小时，卵子在输卵管内能存活８～１０小时。１．２ 公猪精子在射精后２～３小时到达输卵管，并在输卵管上１／３处与卵子交配结合，精子在输卵管内能存活１０～２０ 小时。适宜配种时间，应在排卵前２～３小时，即发情症状开始２０～３６小时。１．３ 母猪发情后，配种过早，卵子与精子相遇时；精子已失去生活力和穿透力，不仅降低受胎率，产仔数，或不受孕，即使受孕，易造成弱仔，死胎，甚至出现木乃伊等不良现象…     

控制外种母猪乏情的综合措施

1 外种母猪的生理特点,国外瘦肉型母猪较我国现有地方母猪性成熟期(第一次发情)晚,在良好的饲养环境下,一般5～6月龄才达到初情期,经屠宰测定第一次发情并不意味着都能排卵,就群体而言,第三次发情才能全部达到排卵。根据饲养和管理情况,后备母猪初次交配的平均年龄应是在7～8月龄,体重达到成年体重的50％～60％,即体重不低于100kg小母猪才开始配种．母猪排卵高潮是在发情中后期,即母猪接受爬跨后24～36h,排卵数占总排卵数的65．97％．     

夜间一次输精可提高受胎率

夜间一次输精可提高受胎率要想提高奶牛的受胎率，就应掌握好配种时间和发情排卵的规律。（一）进行观察记录据观察，我场奶牛发情持续时间为１０－１６小时，也有一部分为６－１０小时（占２５％）。大多数奶牛在性欲消失后１０－１５小时左右排卵。凌晨和夜间排卵的奶牛...     

新嘉系母猪发情的排卵特点研究

新嘉系猪兼具嘉兴黑猪的高产仔特性和丹麦长白与杜洛克猪的优良肉用性能，外国猪血缘成分占６２．５％。经研究，发情征状与外国猪种相似；发情持续期青年母猪为３１．８１±９．８６小时，经产母猪为３８．９±９．１小时，排卵时间最早为发情期结束前２小时，最迟为发情期结束后２６小时；配种适期为发情开始后２４小时配第一次，隔１２小时重配一次。     

猪宝灵的开发和应用研究

将５１头经产母猪随机分成两组，试验组３７头，于断奶后１２小时内注射猪宝灵６００ＩＵ，对照组不作处理，以观察同期发情率，情期受胎率和产仔质量。用猪宝灵分别处理４８头乏情母猪和１２头初情青年母猪，以观察其调节体内激素代谢水平，治疗某些繁殖疾病。研究结果表明：同期发情试验，受试组与对照组之间的同期发情率差异显著（Ｐ＜０．０１）。处理乏情母猪发情率８７．５％（４２／４８）情期受胎率８３．３％（３５／４２），初期青年母猪诱导发情率８３．３％（１０／１２），情期受胎率８０％（８／１０）。确立了猪宝灵处理不同类型母猪，对初情青年母猪有诱导性早熟作用，提高了经产母猪同期发情水平，同时又能有效地治疗乏情母猪，以达到最佳排卵率和较理想受胎率。因此猪宝灵的应用对提高母猪繁殖力，实现工厂化、集约化批次生产商品猪起了积极作用，产生了良好的经济效益，促进了养猪业的发展     

母猪的配种时间和配种频率

母猪的配种时间和配种频率袁森泉广三保养猪有限公司（５１８１０３）利用断奶至发情间隔作为配种时间和配种频率的指标，是提高母猪受胎率和产仔数的有效方法之一。而且母猪适时配种或授精可使每窝产仔数增加３－４头。在母猪排卵１２小时内，甚至在６小时内受精，其窝仔...     

不同授精时间对仔猪性比影响的研究

有研究报道认为，在母牛排卵前授精易得雌性后代，在接近排卵时授精易得雄性后代，在授精当时预测的犊牛性别与实产犊牛性别的符合率达到约７０％。为了检验这一现象是否也存在于猪的繁殖活动，特别安排在同一发情母猪的排卵前和后，分别用不同毛色的公猪配种，观察在不同排卵期授精是否也影响仔猪的性比。为了探讨不同排卵期授精当时的内分泌活动，在二次配种当时分别在尾动脉采血，测定血清中雌二醇和促黄体素含量。２２窝母猪的试验结果表明，排卵前授精得母仔５５．６％（６９／１２４），排卵后授精得公仔５７．３％（７５／１２４），Ｐ＜０．０５。其中有１窝只在排卵前授精（母仔占６９．２％，９／１３）和５窝只在排卵后授精（公仔占６７．４％，２９／４３），更加显著地（Ｐ＜０．０２５）表现出对仔猪性比的影响。激素测定表明，排卵前授精时血清中雌二醇和促黄体素水平分别比排卵后授精高２．３和６．３倍，对测定结果的进一步分析表明，母猪在授精当时血清中雌二醇含量较高时，后代母仔的比例较高。     

母猪配种须选时

要做到适时配种 ,必须掌握母猪发情后的排卵规律。一般母猪在发情后2 4～ 36小时排卵 ,排卵持续时间为 1 0～ 1 5小时 ,卵子排出后在 8～ 1 2小时有受精能力。公猪的精子在母猪的生殖道里可以存活 1 0～ 2 0小时。精子从进入母猪生殖道到游动至输卵管的受精部位需要 2～ 3小时 ,因此 ,给母猪受精配种的适宜时间应在排卵前 2～ 3小时 ,即在发情后 2 0～ 30小时。由于母猪品种、年龄、发情周期长短的不同 ,母猪在发情后的排卵时间也不一致。老年母猪发情时间短 ,排卵时间会提前 ,应提前配种 ;青年母猪发情时间长 ,排卵期会后移 ,故配种时间应…     

LRH－A_3诱导初情期前母猪发情排卵的效果和机理研究

本研究探讨了ＬＲＨ－Ａ３诱导初情期前北京黑猪发情排卵的效果及其内分泌机理。对６头１５０日龄母猪肌注ＬＲＨ－Ａ３，７５μｇ／头。在注射后０，１，２，３和４ｈ及注射后１，２，３和４ｄ采血测定ＬＨ、ＦＳＨ、Ｅ２和Ｐ４浓度。注射后１０ｄ取卵巢，根据卵巢上黄体数计算排卵率。结果表明：注射ＬＲＨ－Ａ３后，出现排卵和卵巢囊肿的母猪分别为４头（６６．７％）和２头（３３．７％）。４头排卵母猪中的３头和２头卵巢囊肿母猪中的１头有发情表现。排卵的母猪，分别在注射后１ｈ和３ｈ出现ＬＨ和ＦＳＨ峰；注射后２ｄＥ２浓度最高，３ｄ和４ｄＰ４浓度上升。发生卵巢囊肿的母猪，注射后１ｈ出现明显低于排卵母猪的ＬＨ峰，而ＦＳＨ浓度没有上升，Ｅ２和Ｐ４在３ｄ和４ｄ都增加。通过试验认为，初情期前母猪的卵巢对ＬＲＨ－Ａ３至少有两种反应，即排卵或卵巢囊肿。     

冬季母猪配种技巧

（一）配种时间 根据母猪排卯时间及卵子、精子运行和存活时间，母猪最适宜的配种时间应是发情后24～48小时，此时受胎率最高。因此，确定母猪最适宜的配种时间，应为母猪排卵前的2～3小时。     

Administration of p.g. 600 to sows at weaning and the time of ovulation as determined by transrectal ultrasound

This study determined whether the interval from estrus to ovulation was altered by giving P.G. 600 to sows at weaning. Mixed-parity sows received P.G. 600 i.m. (n = 72) or no treatment (n = 65) at weaning (d 0). Beginning on d 0, sows were observed for estrus twice daily. At the onset of estrus and thereafter, ultrasound was performed twice daily to determine the average size of the largest follicles and time of ovulation. Weaning age (20.1+/-0.4 d) did not differ (P > 0.10) between treatments. More P.G. 600 sows expressed estrus within 8 d (P < 0.01) than controls (94.4% vs 78.4%, respectively). Parity was associated with expression of estrus (P < 0.02), with 78% of first-parity and 93% of later-parity sows exhibiting estrus. However, no treatment x parity effect was observed (P > 0.10). The interval from weaning to estrus was reduced (P < 0.0001) by P.G. 600 compared with controls (3.8+/-0.1 d vs 4.9+/-0.1 d). Follicle size at estrus was not affected by treatment (P > 0.10). The percentage of sows that ovulated did not differ (P > 0.10) for P.G. 600 and control sows (90.3% vs 81.5%, respectively). Time of ovulation after estrus was not affected by treatment and averaged 44.8 h. However, univariate analysis indicated that the interval from weaning to estrus influenced the interval from estrus to ovulation (r = 0.43, P < 0.0001). Further, multivariate analysis showed an effect of treatment on the intervals from weaning to estrus, weaning to ovulation (P < 0.0001), and estrus to ovulation (P < 0.04). Within 4 d after weaning, 81% of the P.G. 600 sows had expressed estrus compared with 33% of controls. However, this trend reversed for ovulation, with only 35% of P.G. 600 sows ovulating by 36 h after estrus compared with 40% of controls. The estrus-to-ovulation interval was also longer for control and P.G. 600 sows expressing estrus < or = 3 d of weaning (45 h and 58 h, respectively) than for sows expressing estrus after 5 d (39 h and 32 h, respectively). Farrowing rate and litter size were not influenced by treatment. However, the interval from last insemination to ovulation (P < 0.02) indicated that more sows farrowed (80%) when the last insemination occurred at < or = 23 to > or = 0 h before ovulation compared with insemination > or = 24 h before ovulation (55%). In summary, P.G. 600 enhanced the expression of estrus and ovulation in weaned sows but, breeding protocols may need to be optimized for time of ovulation based on the interval from weaning to estrus.     

Responsiveness to boar stimuli and change in vulvar reddening in relation to ovulation in weaned sows

In 117 weaned sows, changes in estrous behavior and vulvar reddening were related to timing of ovulation. Detection of estrus was performed every 8 h with four levels of boar stimuli to record the change in responsiveness to these stimuli. This resulted in four overlapping phases of estrus, during which a standing response could be evoked: 1) man estrus (standing response to a back pressure test, in the absence of a boar), 2) spontaneous estrus (standing response in the presence of a boar, no back pressure test), 3) boar estrus (standing response to boar + back pressure test), and 4) detection-mating-area estrus (back pressure test in the presence of four boars). In addition to the detection of estrus, the change in reddening of the inner vulvar mucosa was recorded. Manifestation of estrus in response to the four stimuli occurred in 46, 56, 90, and 97% of the sows, respectively. Onset of the four phases occurred 24 h (SD 13 h), 23 h (SD 15 h), 34 h (SD 13 h), and 41 h (SD 12 h) before ovulation. The duration of the intervals between the various phases of estrus explained 10 to 50% of the variation in the timing of ovulation relative to the onset of the phases. However, these intervals could not be calculated for all sows because estrus was not expressed at every stimulus level by each sow. The end of vulvar reddening occurred, on average, 21 h (SD 14 h) before ovulation. Except for five sows that ceased to show vulvar reddening within 5 h after ovulation, the end of vulvar reddening occurred before ovulation, within a 70-h range. Of the sows showing boar estrus, 90% also showed vulvar reddening. For sows that showed vulvar reddening until after the onset of boar estrus (two-thirds of the sows), the end of reddening occurred within a much smaller range: from 36 h before, until 2 h after, ovulation. Onset of estrus, regardless at which stimulus level it is detected, appears too variable relative to timing of ovulation to be used as a predictor for ovulation. Duration of the different stages of responsiveness explains only some of this variation and cannot be obtained on all sows. Combining information on vulvar reddening and boar estrus can predict ovulation within a reasonable range for two-thirds of the sows.     

Nutrition for optimizing breeding herd performance.

Modern sows are younger and leaner at time of mating and probably have poorer appetites than sows of 10 to 15 years ago. Therefore, feeding strategies should aim to minimize weight loss and maintain a sow's body condition throughout her reproductive life. The efficiency with which gilts are introduced into the breeding herd is as important in economic terms as is the efficiency with which the sow returns to estrus after weaning. Gilts should be selected at 50 to 60 kg, and fed a 16% protein diet ad libitum until mated at their second estrus, when they weigh 115 to 120 kg and have 17 to 20 mm backfat. Flushing gilts before the onset of second or third estrus increases ovulation rate of restricted gilts to the levels achieved by gilts fed ad libitum. During gestation, maintenance represents 75 to 85% of total energy requirements. The aim should be to achieve 20 to 25 mm backfat at farrowing. Increased feed intake from day 2 to 3 after mating will not increase embryo mortality. Feeding an extra 1 kg feed/sow/day for the last 10 days of gestation increases piglet birth weight slightly and prevents a loss of 1.5 to 2.0 mm of sow backfat. Wherever possible, sows should be fed ad libitum from the day after farrowing until weaning. Reduced feed intake by lactating sows, for whatever reason, results in excessive weight and condition loss. Excessive weight loss in lactation causes extended remating intervals, a lower percentage of sows returning to estrus within 10 days of weaning, reduced pregnancy rate, and reduced embryo survival. Ovulation rate is not affected by level of feed intake in lactation. It has been suggested that sows will have minimum weaning-to-service intervals when they weigh 150 kg or more at weaning. It is likely that the sow must be anabolic for about 10 days before she will exhibit postweaning estrus. The decision when to rebreed is made some time prior to weaning and is mediated by a host of substrates, hormones, and neurotransmitters. Sows with a delayed return to estrus also have a lower pregnancy rate and smaller subsequent litters. If sows lose considerable weight or condition during lactation, a high level of feeding in the postweaning period will improve embryo survival.     

Efficacy of using vaginal conductivity as an indicator of the optimum time to breed in swine

Two experiments were conducted to test the efficacy of using vaginal conductivity measurements to predict ovulation time in swine. In Exp. 1, 10 normally cycling 6-mo-old purebred Hampshire gilts were tested daily through two estrous cycles in order to characterize conductivity patterns. In all females, onset of behavioral estrus was verified by daily observation in the presence of a sexually active boar. Significant changes in vaginal conductivity by day of the cycle were detected in all females tested, with a high degree of variation among individuals. A 10% increase in conductivity occurred 12 to 24 h after the onset of estrus, which is coincident with the time normally associated with high fertility. In Exp. 2, 46 prepubertal crossbred and purebred Yorkshire gilts and 17 multiparous purebred Yorkshire and Duroc sows were assigned randomly to eight treatment groups. All females were checked twice daily for the onset of estrus and vaginal conductivity readings were taken from approximately 3 d before estrus until breeding. Females were bred by artificial insemination or handmated at times determined either by detection of estrus alone or when a 10% increase in conductivity readings occurred relative to the onset of estrus. Similar conception rates were achieved in animals bred after a 10% change in vaginal conductivity as compared with detection of estrus. These results indicate that vaginal conductivity measurements during estrus provided a reliable basis for determining the time to breed swine. However, there was no advantage associated with the use of vaginal conductivity.     

Effects of ACTH injections during estrus on concentrations and patterns of progesterone, estradiol, LH, and inhibin alpha and time of ovulation in the sow

This study investigated whether injections of ACTH for 48 h, from the onset of the second standing estrus after weaning, had any impact on time of ovulation and patterns of progesterone, estradiol, luteinizing hormone (LH), and inhibin alpha. The studied sows (n=15) were fitted with jugular vein catheters and randomly divided into a control (C group) and an ACTH group. From the onset of standing estrus, the sows were injected (NaCl or synthetic ACTH, 5 microg/kg) every 4h; blood samples were collected immediately before and 45 min after each injection. Ovulation was monitored using ultrasonography. The ACTH-group sows stopped displaying signs of standing estrus sooner after ovulation in their second estrus, but no impact was found on time of ovulation. There were no significant differences in the intervals between LH peak, estradiol peak, and the onset of standing estrus between the C and ACTH groups. The cortisol and progesterone concentrations were significantly elevated (p<0.001) in samples taken 45 min after ACTH injection. There were minor differences in estradiol and LH concentrations between the groups. Overall inhibin alpha concentrations were significantly higher during the treatment period in the ACTH than in the C group, but there were no significant differences between samples taken either 45 min or 4h after injection. In conclusion, injections of synthetic ACTH during estrus in the sow apparently disturb the duration of signs of standing estrus and the hormonal pattern of progesterone, and possibly of inhibin alpha, estradiol and LH.     

Duration of estrus in relation to reproduction results in pigs on commercial farms.

This research was conducted to determine factors that influence duration of estrus, AI strategy, and reproduction results between and within commercial swine farms that use AI. Data from 15,186 sows and gilts on 55 farms for a period of 6.1+/-4.2 mo per farm were used in this study. The average duration of estrus was 48.4+/-1.0 h, ranging from 31 to 64 h, and was consistent from month to month within a farm (repeatability of 86%). Differences in duration of estrus between farms accounted for 23% of the total variation in duration of estrus. On most farms (n = 45), gilts showed a shorter (P < .05) duration of estrus than sows (40.8+/-1.1 h vs 48.5+/-1.0 h). The duration of first estrus after weaning was longer (P < .0001) compared with that of repeat-breeder sows (50.2+/-1.0 h vs 46.8+/-1.0 h). Duration of estrus decreased (P < .05) when interval from weaning to estrus increased from 4 to 6 d (56.0 +/- 1.2 h vs 45.8 +/-1.2 h). The regression of interval from onset to estrus to first AI and interval from weaning to estrus varied between farms and ranged from -7.4 to +1.3 h/d; four farms had a positive relationship. Farrowing rate decreased (P < .05) from 89.7+/-2.7% to 78.2+/-5.74 when the interval from weaning to estrus increased from 4 to 10 d. The litter size decreased (P < .05) from 11.7 to 10.6 pigs when the interval from weaning to estrus increased from 4 to 7 d. Compared with a single AI, double AI in sows and gilts resulted in a 4.3 and 7.0% higher (P < .05) farrowing rate, respectively. When the first AI was performed after expected ovulation, reproduction results were lower than when AI was performed before or at expected ovulation in sows. Duration of estrus was not related to farrowing rate or litter size in individual pigs. Number of inseminations per estrus, time of AI, and duration of estrus were correlated, which made it difficult to assess which of these factors was primarily related to the farrowing rate or litter size. Knowledge of average duration of estrus on farms and of factors that influence the duration of estrus on commercial farms can help to improve the efficiency of the AI strategy specific for each farm.     

Effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest

We previously reported that ovulation rate, but not pregnancy rate or litter size at d 30 after mating, was enhanced by treatment with P.G. 600 (400 IU of PMSG and 200 IU of hCG, Intervet America, Inc., Millsboro, DE) in gilts fed the orally active progestin, altrenogest (Matrix, Intervet America, Inc.) to synchronize estrus. We hypothesized that in addition to increasing ovulation rate, P.G. 600 may have altered the timing of ovulation. Therefore, mating gilts 12 and 24 h after first detection of estrus, as is common in the swine industry, may not have been the optimal breeding regimen, and as a consequence, pregnancy rate and litter size were not altered. The objective of the present study was to determine the effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest. Randomly cycling, crossbred gilts (5.5 mo old, 117 kg BW, and 14.7 mm of backfat) were fed a diet containing altrenogest (15 mg/d) for 18 d. Twenty-four hours after altrenogest withdrawal, gilts received i.m. injections of P.G. 600 (n = 25) or saline (n = 25). Gilts were checked for estrus at 8-h intervals. After first detection of estrus, transrectal ultrasonography was performed at 8-h intervals to determine the time of ovulation. Gilts were killed 9 to 11 d after the onset of estrus to determine ovulation rate. All gilts displayed estrus by 7 d after treatment with P.G. 600 or saline. Compared with saline, P.G. 600 increased (P = 0.07) ovulation rate (14.8 vs. 17.5, respectively; SE = 1.1). The intervals from injection to estrus (110.9 vs. 98.4; SE = 2.7 h; P < 0.01) and injection to ovulation (141.9 vs. 128.6; SE = 3.2 h; P < 0.01) were greater in gilts treated with saline than in gilts treated with P.G. 600. Duration of estrus (54.4 vs. 53.7; SE = 2.5 h), the estrus-to-ovulation interval (30.2 vs. 31.7; SE = 2.2 h), and the time of ovulation as a percentage of estrus duration (55.8 vs. 57.5; SE = 3.0%) did not differ for the P.G. 600 and saline-injected gilts, respectively. In summary, P.G. 600 advanced the onset of estrus and ovulation following termination of altrenogest treatment and increased ovulation rate; however, treatment of gilts with P.G. 600 had no effect on the timing of ovulation relative to the onset of estrus.     

Effects of boar contact and housing conditions on estrus expression in weaned sows

Our objective was to study the effects of housing conditions and the amount of boar contact in a protocol for estrus detection on estrus detection rate, timing of onset of estrus, duration of estrus, and timing of ovulation. After weaning, 130 multiparous sows were assigned to three treatments: HI, in which 52 sows were housed individually in crates and received a high amount of boar contact during estrus detection; HG, in which 52 sows were housed in groups and received a high amount of boar contact; and NI, in which 26 sows were housed individually in crates and received a normal amount of boar contact. Estrus detection was performed every 8 h. For each treatment, the standing response to three levels of stimuli was recorded: a back pressure test (BPT) by a man (man-estrus), presence of a teaser boar (spontaneous-estrus), and BPT in the presence of a teaser boar (boar-estrus). In addition, for HI and HG, the standing response to a fourth level of stimuli was recorded: BPT in a detection-mating area, surrounded by four boar pens (DMA-estrus). To detect ovulation, ultrasonography was performed every 4 h during estrus. Of 117 sows that ovulated, 46% showed man-estrus, 56% spontaneous-estrus, 90% boar-estrus, and 97% DMA-estrus. Mean onset of man-estrus was 107 h (SD 26) after weaning, of spontaneous-estrus was 106 h (SD 22) after weaning, of boar-estrus was 99 h (SD 21) after weaning, and of DMA-estrus was 93 h (SD 22) after weaning. Duration of man-estrus was 22 h (SD 14), of spontaneous-estrus was 29 h (SD 16), of boar-estrus was 42 h (SD 20), and of DMA-estrus was 55 h (SD 18). The high amount of boar contact reduced the number of sows showing man-estrus (P < .05; 41% for HG and HI vs 68% for NI) and reduced duration of boar-estrus (P < .05; 43 h for HG and HI vs 52 h for NI). Duration of DMA-estrus for HG and HI was similar to duration of boar-estrus for NI. Onset of estrus and timing of ovulation were not affected by amount of boar contact. Group housing did not affect detection rate and duration of estrus, but it did postpone average onset of estrus by 10 h, paralleled by a postponement of ovulation. In conclusion, estrus expression is similar at the highest level of stimuli in different protocols for estrus detection. Including higher levels of stimuli in a protocol reduces estrus expression at lower levels of stimuli. This reduction indicates adaptation of sows to a given protocol for estrus detection. Group housing can delay ovulation and related behavioral estrus.     

Decreased follicular size during late lactation caused by treatment with charcoal-treated follicular fluid delays onset of estrus and ovulation after weaning in sows

The weaning to estrus and weaning to ovulation intervals in sows are controlled by ovarian follicular growth after weaning. Longer intervals could be caused by smaller diameter follicles at weaning that take more time to reach a preovulatory size. We addressed this hypothesis by decreasing the diameter of follicular populations before weaning and then measuring follicular development and interval to estrus and ovulation after weaning. The posterior vena cava, cranial to the entry of the ovarian vein, was cathetered for blood sampling and infusion in 20 sows at 12 +/- 1 d after farrowing. Sows were assigned randomly to receive either 30 mL of charcoal-treated follicular fluid (FF, n = 9; a treatment known to decrease serum FSH and follicular diameter) or 30 mL of saline (n = 11) by venous infusion thrice daily (0700, 1500, and 2300 h) for 96 h beginning at 14 +/- 1 d after farrowing. Sows were weaned 48 h after the last infusion. Blood samples were collected for FSH analysis thrice daily beginning on the day of catheterization and continuing until ovulation. Follicular diameter was determined once daily by transrectal ultrasonography. A treatment x time interaction was detected for serum FSH (P < 0.001) and follicular diameter (P < 0.001) because serum FSH and the diameter of follicular populations decreased in FF sows during the infusion period. After the infusion period, serum FSH rebounded in FF sows, and follicles resumed growth but grew at the same rate as those of saline-treated sows, thus failing to achieve equivalent diameters relative to saline-treated sows on a given day after weaning. As a result, sows treated with FF had longer (P < 0.05) weaning to estrus (6.1 +/- 0.4 d) and weaning to ovulation (8.6 +/- 0.5 d) intervals compared with saline-treated sows (4.7 +/- 0.4 d and 7.2 +/- 0.4 d, respectively). We conclude that the diameter of the follicular population at weaning is one factor that controls interval to estrus and ovulation in sows. Small follicles at weaning cannot undergo compensatory growth and require additional time to reach a preovulatory size.     

Effect of frequency of boar exposure and adjusted mating times on measures of reproductive performance in weaned sows

In weaned sows, reduced reproductive performance can result from failure or delayed return to estrus or improper timing of insemination. This experiment evaluated the effect of increased frequency of boar exposure and adjusted mating times on reproductive performance. Sows of mixed parity were weaned approximately 18.7 d after parturition and allotted by genotype, parity, and lactation length to boar exposure frequency of once daily (1X, n = 66), twice daily every 12 h (2X, n = 61), or three times daily exposure at 8-h intervals (3X, n = 60). Sows were weaned into crates and boar exposure was initiated 3 d after weaning. Once estrus was detected, ultrasound was performed every 8 h to determine time of ovulation. All sows were artificially inseminated twice in the 1X group at 0 and 24 h, in the 2X group at 12 and 24 h, and in the 3X group at 16 and 32 h after onset of estrus. The weaning-to-estrus interval was not influenced by treatment and averaged 4.5 d. The percentage of sows expressing estrus in 8 d was higher (P < 0.05) for 1X (97.3%) compared with 2X (92.8%) but not the 3X group (94.0%). The percentage of sows ovulating after estrus was not influenced by treatment (P > 0.10) and averaged 96.5%. Estrus-to-ovulation interval was not affected by treatment (44.7 h) but was influenced by weaning-to-estrus interval (P < 0.0001). Length of estrus was influenced by treatment (P < 0.001), with estrus in the 1X (46.6 h) shorter than in the 2X (60.0 h) and 3X (67.0 h) treatments, and also by weaning-to-estrus interval (P < 0.001). The percentage of first inseminations occurring within 24 h before ovulation was increased (P < 0.001) in the 2X (62%) and 3X (66%) groups compared with the 1X group (28%) and was also influenced by parity (P < 0.001) and weaning-to-estrus interval (P < 0.05). The percentage of second services within 24 h before ovulation was not increased by any factor and averaged 78%. Farrowing rates were not increased (P > 0.10) for 2X (87.2%) and 3X (83.1%) treatments compared with 1X (75.0%). Total pigs born was also not affected by treatment, although 2X (11.2) and 3X (10.7) numbers were greater than 1X (10.0). It appears that once-daily estrus detection combined with delayed mating could achieve optimal reproductive performance.