Influence of time of insemination relative to ovulation and frequency of insemination on gilt fertility

The objectives of this study were to determine the optimal time of insemination in the pre-ovulatory period (from 32 to 0 h before ovulation) and to evaluate once-daily versus twice-daily inseminations in gilts. In Experiment 1, pre-puberal gilts (n=102) were observed for estrus every 8h and ultrasonography was performed every 8h from the onset of estrus to confirmation of ovulation. The gilts were inseminated once with 4 x 10(9) spermatozoa at various intervals prior to ovulation. Pregnancy detection was conducted 24 days after AI and gilts were slaughtered 4-6 days later. Corpora lutea and the number of viable embryos were counted and the embryo recovery rate was calculated (based on the percentage of corpora lutea). Inseminations performed <24h before ovulation resulted in a higher embryo recovery rate (P=0.02) and produced 2.1 more embryos (P=0.01) than inseminations >or=24h before ovulation. However, the pregnancy rate was reduced when inseminations were performed >16 h before ovulation (P=0.08). In Experiment 2, pre-puberal gilts (n=105) were observed for estrus every 12h and ultrasonography was performed every 12h from the onset of estrus to confirmation of ovulation. Gilts were inseminated (with 4 x 10(9) spermatozoa) 12h after the onset of estrus, with inseminations repeated either every 12h (twice-daily) or 24h (once-daily) during estrus. The gilts were allowed to farrow. There were no differences (between gilts bred twice-daily versus once-daily) for return to estrus rate (P=0.36) and adjusted farrowing rate (P=0.19). However, gilts inseminated once-daily had 1.2 piglets less than those inseminated twice-daily (P=0.09). In conclusion, gilts should be inseminated up to 16 h before ovulation, as intervals >16 h reduced pregnancy rate and litter size.     

Effect of time of insemination relative to ovulation on fertility with liquid and frozen boar semen

Precise data on fertility results following peri- and postovulatory insemination in spontaneously ovulating gilts is lacking. Using transcutaneous sonography every 4 h during estrus as a tool for diagnosis of ovulation, the effects of different time intervals of insemination relative to ovulation were investigated with liquid semen (Experiment 1, n=76 gilts) and frozen semen (Experiment 2, n=80 gilts). In Experiment 3 (n=24 gilts) the number of Day-28 embryos related to the various intervals between insemination and ovulation was determined after the use of liquid semen. Using liquid semen the fertilization rates based on Day-2 to Day-5 embryos and the number of accessory spermatozoa decreased significantly in gilts inseminated with 2 x 10(9) spermatozoa per dosage in intervals of more than 12 h before or more than 4 h after ovulation. In the time interval 4 to 0 h before ovulation, comparable fertilization rates were obtained using frozen semen (88.1%) and liquid semen (92.5%). Fertilization rates and numbers of accessory spermatozoa decreased significantly when gilts were inseminated with frozen semen more than 4 h before or 0 to 4 h after the detection of ovulation. The percentage of Day-28 embryos was significantly higher following preovulatory insemination compared to inseminations 0 to 4 h and 4 to 8 h after ovulation. It is concluded that the optimal time of insemination using liquid semen is 12 to 0 h before ovulation, and 4 to 0 h before ovulation using frozen semen. The results stress the importance of further research on sperm transport and ovulation stimulating mechanisms, as well as studies on the time of ovulation relative to estrus-weaning intervals and estrus duration.     

Fertility of Deep Frozen Boar Spermatozoa at Various Intervals between Insemination and Induced Ovulation

This study was performed to investigate the influence of boars and thawing diluents on the fertilizing capacity of deep frozen spermatozoa at various intervals between inseminations and ovulation. Forty-four Swedish crossbred gilts were inseminated following injection of HCG late in the prooestrus. Inseminations were performed 22, 28, 34 and 38 hrs. after injection of HCG. Ovulation was expected to occur 40 hrs. after injection of HCG. Two boars, previously tested for fertility with frozen semen, supplied the spermatozoa. Roar seminal plasma and OLEP were utilized as thawing diluents. The gilts were slaughtered 32–48 hrs. after estimated ovulation. The genital tracts were removed immediately after stunning and bleeding and the numbers of recent ovulations, recovered ova and fertilized ova were recorded. Additionally recovered ova were classified according to estimated numbers of spermatozoa attached to the zona pellucida. Similar fertilization rates were obtained when inseminations were performed 2 and 6 hrs. before estimated ovulation. A clear decline in fertility appeared when inseminations were performed earlier than 6 hrs. before expected ovulation. The results were influenced by the boars as well as by the thawing diluents. Seminal plasma yielded a higher fertilization rate than OLEP in inseminations performed 2 hrs. before estimated ovulation. The boars yielded similar fertility in inseminations performed 2 hrs. before estimated ovulation. With increasing intervals between inseminations and ovulation the difference between the boars increased. The single gilt in which fertilized ova were found after insemination 18 hrs. before ovulation was inseminated with spermatozoa from the superior boar, thawed in seminal plasma. The present results indicate that spermatozoa with low resistance to freezing-thawing have a short fertile life in the female genital tract after insemination.     

Effect of sperm number and frequency of insemination on fertility of mares inseminated with cooled semen

In this study, we tested the hypothesis that insemination of mares with twice the recommended dose of cooled semen (2 x 10(9) spermatozoa) would result in higher pregnancy rates than insemination with a single dose (1 x 10(9) spermatozoa) or with 1 x 10(9) spermatozoa on each of 2 consecutive days. A total of 83 cycles from 61 mares was used. Mares were randomly assigned to 1 of 3 treatment groups when a 40-mm follicle was detected by palpation and ultrasonography. Mares in Group 1 were inseminated with 1 x 10(9) progressively motile spermatozoa that had been cooled in a passive cooling unit to 5 degrees C and stored for 24 h. A second aliquot of semen from the same collection was stored for an additional 24 h and inseminated at 48 h after collection. Mares in Group 2 were inseminated once with 1 x 10(9) progressively motile spermatozoa that had been cooled to 5 degrees C and stored for 24 h. Group 3 mares were inseminated once with 2 x 10(9) progressively motile spermatozoa that had been cooled to 5 degrees C and stored for 24 h. All mares were given 2500 IU i.v. hCG at the first insemination. Pregnancy was determined by ultrasonography 12, 14 and 16 d after ovulation. On Day 16, mares were administered i.m. 10 mg of PGF2 alpha and, upon returning to estrus, were randomly reassigned to a group for repeated treatment. Semen was collected from one of 3 stallions every 3 d; mares with a 40-mm ovarian follicle were inseminated with semen from the stallion collected on the preceding day. Semen was allocated into doses containing 1 x 10(9) progressively motile spermatozoa, diluted with dried skim milk-glucose extender to a concentration of 25 x 10(6) motile spermatozoa/ml (total volume 40 ml), placed in a passive cooling unit and cooled to 5 degrees C for 24 or 48 h. Response was measured by number of mares showing pregnancy. Data were analyzed by Chi square. Mares inseminated twice with 1 x 10(9) progressively motile spermatozoa on each of two consecutive days had a higher pregnancy rate (16/25, 64%; P < 0.05) than mares inseminated once with 1 x 10(9) progressively motile spermatozoa (9/29, 31%) or those inseminated once with 2 x 10(9) progressively motile spermatozoa (12/29, 41%). Pregnancy rates did not differ significantly (P > 0.10) among stallions (69, 34 and 32%). Interval from last insemination to ovulation was 0.9, 2.0 and 2.0 d for mares in Groups 1, 2 and 3, respectively. Based on these results, the optimal insemination regimen is a dose of 1 x 10(9) progressively motile spermatozoa given on two consecutive days. However, a shorter interval (< or = 24 h rather than > 0.9 d) between insemination and ovulation may affect pregnancy rates, and needs to be investigated.     

The time of ovulation in relation to estrus duration in gilts

The objective of this study was to determine time of ovulation, monitored by transcutaneous ultrasonography, relative to the duration of estrus in gilts. We exposed 92 cyclic gilts, Camborough x Canabrid terminal line, at Day 19 of their third estrous cycle to vasectomized boars every 6 h for the detection estrus. Transcutaneous ultrasonography was performed every 6 h, starting 24 h after the onset estrus, to determine time of ovulation. Estrus duration was, on average, 52.6 h (range: 30 to 72 h), and ovulation occurred between 30 and 60 h after the onset of estrus (mean: 44 h), about 85 % of the way through the estrus period. The time of ovulation during estrus was dependent on the duration of estrus (Time of ovulation = (duration of estrus) x 0.409 + 22.7; r = 0.57, P = 0.0001). Prediction of the time of ovulation in relation to duration of estrus is important for determining the optimal time for inseminating gilts. This knowledge would contribute to an improvement in the fertilization rate and in reproductive efficiency of the breeding herd.     

Selected times of insemination with microencapsulated bovine spermatozoa affect pregnancy rates of synchronized heifers

This experiment was designed to test whether spermatozoa encapsulated in an alginate poly-L-lysine matrix had an extended fertile life in vivo after insemination. Estrus was synchronized in 417 primiparous Friesian and Jersey heifers with a system based on a CIDR-B intravaginal device before the heifers were inseminated either during proestrus (24 h after device removal) or at estrus (48 h after device removal). Pregnancy rates to first inseminations did not differ between the 24 and 48 h inseminations (61 vs 60.6%) with liquid semen diluted in Caprogen (control) but differed with encapsulated semen (45.1 vs 68.6%). The difference in pregnancy rates between the 2 types of semen was more pronounced (P < 0.08) in the animals that were visually detected in estrus. The mean survival time of spermatozoa in the female reproductive tract following insemination at the 24-h insemination time was estimated to be 50 +/- 7.5 h. The increased pregnancy rate with insemination of encapsulated spermatozoa at 48 h could have been due to this process predisposing spermatozoa to capacitate soon after insemination.     

Low dose insemination in synchronized gilts

Conventional insemination techniques in pigs require 2 to 3 x 10(9) sperm/dose. When using the latest high-speed sperm-sorting technology, one can still sort only about 5 to 6 million sperm of each sex per hour. The objective of the present study was to find the minimal sperm concentration at a low-insemination volume in pigs without diminishing fertilization rate and litter size using surgical deep intra-uterine insemination (IUI). Semen from 3 boars was collected and diluted with Androhep to 5 x 10(8), 1 x 10(8), 1 x 10(7), 5 x 10(6) or 1 x 10(6) sperm/0.5 ml. In trial 1, 109 prepuberal gilts were synchronized and surgically inseminated into the tip of each uterine horn 32 h or 38 h after hCG treatment or at the time of ovulation, respectively. Pregnant gilts were allowed to go to term. Pregnancy and farrowing rates did not differ significantly except at the lowest sperm concentration if inseminated 32 h or 38 h after hCG treatment (p < 0.05). No differences were found among insemination groups for the total number of piglets, number of piglets born alive, stillborn piglets, and mummified fetuses. In trial 2, 34 gilts were inseminated as described above 32 h after hCG. Additionally, 9 gilts were inseminated once nonsurgically with 1 x 10(9) sperm as controls. Gilts were slaughtered 48 h after insemination, and embryos were recovered. Embryos were cultured in NCSU 23 (120 h), evaluated morphologically and stained with fluorescent dye (Hoechst 33342) to visualize nuclei. Recovery rates varied between 71.4% and 84.4%. Fertilization rate of the lowest sperm concentration (1 x 10(6) sperm/horn) differed significantly (p < 0.05) from all other groups. Cleavage rates at specific developmental stages did not differ. After 5 days of in vitro culture, embryos developed to morulae and blastocysts. No differences were found for these stages. In conclusion, no major differences were found between insemination groups as long as the sperm dosage was at least 10 million sperm per gilt. The low volume was sufficient for successful deep intra-uterine insemination. Embryo development was comparable to the controls.     

The influence of time of insemination relative to time of ovulation on farrowing frequency and litter size in sows, as investigated by ultrasonography

The objective of this experiment was to identify the optimal time of insemination relative to the time of ovulation, based on ultrasonographic detection of embryonic survival at 10 days after ovulation, number of sows farrowing, and litter size. Furthermore, the possible value of the interval from weaning to onset of estrus for prediction of the time of ovulation was examined. Crossbred sows (n = 143) that had farrowed 2 to 9 litters were weaned (Day 0) and observed for estrus every 8 h from Day 3 until end of estrus. Ultrasonography was performed every 6 h, from 12 h after onset of estrus until ovulation had been observed. The sows were inseminated once at various time intervals from ovulation. At Day 16, 25 of the sows were slaughtered and their uteri were flushed for embryos. In the remaining sows, the number of viable and dead piglets and mummified fetuses per sow was recorded at farrowing, with the sum of the 3 constituting the total number of piglets born per sow. The highest number of embryos recovered per sow was found after insemination during the interval from 24 h before to 4 h after ovulation. The lowest frequency of non-pregnant sows and the highest total number of piglets born per sow were found after insemination from 28 h before to 4 h after ovulation. Consequently, the optimal time for insemination was found to be in the interval 28 h before to 4 h after ovulation. The interval from weaning to onset of estrus and from onset of estrus to ovulation were negatively correlated, allowing a rough prediction of the time of ovulation from the interval from weaning to onset of estrus.     

Production of piglets with sexed semen employing a non-surgical insemination technique

The aim of the present study was to ascertain whether multiparous sows could successfully be inseminated with sexed semen non-surgically. Spermatozoa were stained with Hoechst 33342 and separated flowcytometrically in X- and Y-chromosome bearing sperm populations employing the Beltsville Sperm Sexing Technology (BSST). After weaning, estrus was induced in sows with PMSG and hCG. Animals were inseminated once per estrus non-surgically with a specially designed catheter into the tip of the uterine horn, employing 50x10(6) of either sexed or non-sexed spermatozoa diluted in 2 ml Androhep. Pregnant sows were allowed to go to term. Mean pregnancy rate from inseminations with unsexed spermatozoa was 54.5% whereas inseminations with sexed spermatozoa resulted in 33.3% pregnant sows. All but one piglet born after insemination with sexed semen were of the predicted sex. The sex of those piglets born after inseminations with non-sexed spermatozoa was 61.1% for male and 38.9% for female sex. It is concluded that non-surgically inseminations with flowcytometrically sexed spermatozoa can be conducted successfully.     

The effects of administration of gonadotrophins and estrogens on prenatal survival in gilts

In gilts ovulation occurs over a 4 to 8-hour period, with 70% of the ova being shed over a relatively short span of time. These oocytes supposedly give rise to more developed embryos at Days 10 to 12 which advance the uterine environment and reduce survival rates of less developed embryos because of an asynchronous environment. The aim of this experiment was to reduce embryo mortality by influencing the duration and pattern of ovulation. Crossbred gilts (n = 98) were bred at their first observed estrus after being exposed to boars at 200 days of age. Estrus detection was carried out daily at 0000, 0800 and 1600 hours. All gilts were artifically inseminated with fresh semen, with a minimum of 2.7 billion spermatozoa, at both 16 and 32 hours after detection of estrus. Gilts were randomly assigned to one of the following treatments at detection of estrus: 1) 500 IU (2ml) chorionic gonadotrophin (hCG) injected intravenously at the onset of estrus (n = 22); 2) 16 mug (4 ml) gonadotrophin releasing hormone (GnRH) injected intravenously at the onset of estrus (n = 25); 3) 11.5 mug estrogen added to the semen at the time of AI (n = 25); 4) control, untreated gilts (n = 26). All gilts were slaughtered at Day 30 of gestation (Day 0 = day of detected estrus). The mean (+/-SEM) number of ovulations in pregnant gilts per treatment was 13.0 +/- 0.52, 12.6+/-0.51, 13.6+/-0.54 and 13.3+/-0.52, while the mean (+/-SEM) number of normal embryos per treatment was 10.3+/-0.67, 10.5+/-0.66, 10.3 +/- 0.69 and 10.5 +/- 0.67 for hCG, GnRH, estrogen and control groups, respectively, for an embryonic survival rate of 80 +/- 4.2%, 83 +/- 4.1%, 74 +/- 4.3% and 79+/-4.2% in pregnant gilts. If nonpregnant gilts are included, the embryonic survival rate for treatments 1 to 4 was 76+/-7.0%, 73+/-6.5%, 60+/-6.5%, and 64+/-6.4%, respectively. There was no significant difference between treatments for any of these variables. There was no evidence that administration of hCG, or GnRH at the onset of estrus, or the addition of estrogen to semen improved embryonic survival in gilts by Day 30 in this experiment.     

The initial fertilizing capacity of longerm-stored liquid boar semen following pre- and postovulatory insemination

In pigs, high variation is seen in the duration of estrus and in the time of ovulation. This is one of a wide range of factors not related to semen quality, which possibly influences the results of field insemination trials. Experiment 1 (n=81 gilts) was performed to determine the influence of the time of ovulation on the fertilizing capacity of liquid boar semen stored up to 118 h. The objective of Experiment 2 (n=102 gilts) was to study the fertilizing potential of semen stored up to 120 h in 2 different extenders, Androhep and Beltsville Thawing Solution (BTS), by means of postovulatory AI. Inseminations were performed 0 to 4 h after ovulation in order to standardize the trial conditions. Fertilization rates based on Day-2 to Day-4 embryos, and the number of accessory spermatozoa per zona pellucida did not differ between semen stored for 0 to 48 and 48 to 87 h in gilts ovulating within 12 after insemination (Experiment 1). Gilts with an interval of 12 to 24 h between AI and ovulation had lower fertility results using semen stored for more than 48 h. A further decrease was observed when semen storage exceeded 87 h in those gilts ovulating later than 24 h after insemination. The time of ovulation has to be considered as being a major factor of variation in the fertility results of AI trials. In Experiment 2, fertilization rates and numbers of accessory spermatozoa decreased between semen stored for 0 to 24 and 24 to 48 h in BTS, and between semen stored for 0 to 24 and 48 to 72 h in Androhep. Significant differences in fertility between diluents were seen only when using semen stored for more than 96 h, with semen extended with Androhep giving the higher results. The results indicate that the decrease in fertilizing capacity due to in vitro aging of spermatozoa cannot be prevented even during the first days of storage.     

The effects of different insemination regimes on fertility in mares

This study investigated the effects of different artificial insemination (AI) regimes on the pregnancy rate in mares inseminated with either cooled or frozen-thawed semen. In essence, the influence of three different factors on fertility was examined; namely the number of inseminations per oestrus, the time interval between inseminations within an oestrus, and the proximity of insemination to ovulation. In the first experiment, 401 warmblood mares were inseminated one to three times in an oestrus with either cooled (500 x 10(6) progressively motile spermatozoa, stored at +5 degrees C for 2-4 h) or frozen-thawed (800 x 10(6) spermatozoa, of which > or =35% were progressively motile post-thaw) semen from fertile Hanoverian stallions, beginning -24, -12, 0, 12, 24 or 36 h after human chorionic gonadotrophin (hCG) administration. Mares were injected intravenously with 1500 IU hCG when they were in oestrus and had a pre-ovulatory follicle > or =40mm in diameter. Experiment 2 was a retrospective analysis of the breeding records of 2,637 mares inseminated in a total of 5,305 oestrous cycles during the 1999 breeding season. In Experiment 1, follicle development was monitored by transrectal ultrasonographic examination of the ovaries every 12 h until ovulation, and pregnancy detection was performed sonographically 16-18 days after ovulation. In Experiment 2, insemination data were analysed with respect to the number of live foals registered the following year. In Experiment 1, ovulation occurred within 48 h of hCG administration in 97.5% (391/401) of mares and the interval between hCG treatment and ovulation was significantly shorter in the second half of the breeding season (May-July) than in the first (March-April, P< or =0.05). Mares inseminated with cooled stallion semen once during an oestrus had pregnancy rates comparable to those attained in mares inseminated on two (48/85, 56.5%) or three (20/28, 71.4%) occasions at 24 h intervals, as long as insemination was performed between 24 h before and 12 h after ovulation (78/140, 55.7%). Similarly, a single frozen-thawed semen insemination between 12 h before (31/75, 41.3%) and 12 h after (24/48, 50%) ovulation produced similar pregnancy rates to those attained when mares were inseminated either two (31/62, 50%) or three (3/9, 33.3%) times at 24 h intervals.In the retrospective study (Experiment 2), mares inseminated with cooled semen only once per cycle had significantly lower per cycle foaling rates (507/1622, 31.2%) than mares inseminated two (791/1905, 41.5%), three (464/1064, 43.6%) or > or =4 times (314/714, 43.9%) in an oestrus (P< or =0.001). In addition, there was a tendency for per cycle foaling rates to increase when mares were inseminated daily (619/1374, 45.5%) rather than every other day (836/2004, 42.1%, P = 0.054) until ovulation.It is concluded that under conditions of frequent veterinary examination, a single insemination per cycle produces pregnancy rates as good as multiple insemination, as long as it is performed between 24 h before and 12 h after AI for cooled semen, or 12 h before and 12 h after AI for frozen-thawed semen. If frequent scanning is not possible, fertility appears to be optimised by repeating AI on a daily basis.     

Insemination Results with Slow-Cooled Stallion Semen Stored for approximately 40 Hours

Semen from 3 stallions was extended using 2 methods (Kenney extender and a modified Kenney extender), slowly cooled, and stored for 41 ± 6 (s.d.) h before insemination. An insemination dose (40 ml) contained 1.5-2 billion spermatozoa. In the experiment, 26 mares were inseminated in 30 cycles. The pregnancy rate per cycle obtained with sperm stored in the Kenney extender was 87% (n=15). When the semen was extended with the modified extender, centrifuged and stored, the pregnancy rate was 60% (n=15). Inseminations were done every other day until ovulation was detected. If a mare ovulated more than 24 h after the last insemination, she was inseminated also after ovulation. The single-cycle pregnancy rate was 58% when the mares were inseminated only before ovulation (n=19) but the rate was 100% when the inseminations were done both before and after ovulation (n=9) or only after ovulation (n=2). The difference in pregnancy rates was significant (p<0.05), indicating that postovula-tory inseminations probably serve to ensure the pregnancies. The extending and handling methods used in this study resulted in a combined pregnancy rate of 73%, and appear thus to be useful for storing stallion semen for approximately 2 days.     

Low semen dose intracornual insemination of cows at fixed time after PGF2alpha treatment or at spontaneous estrus

The numbers of spermatozoa per insemination and the site of semen deposition in the uterine horn appear to interact to influence pregnancy rate. In two experiments, the effect of a single low dose (2 x 10(6) spermatozoa) intracornual insemination (LD-ICI) on bovine pregnancy rate was compared with that of intracornual (SD-ICI) and conventional (SD-AI) inseminations of 40 x 10(6) spermatozoa. In Experiment 1, 157 cows were treated twice with PGF(2)alpha at a 14-day interval and inseminated at a fixed time (80-82 h) after the second PGF(2)alpha injection using LD-ICI (n=44), SD-ICI (n=61) or SD-AI (n=52). In LD-ICI and SD-ICI groups, semen was deposited in the horn ipsilateral to the ovulatory follicle close to the utero-tubal junction (LD-ICI-UTJ, n=33 and SD-ICI-UTJ, n=41) or in the middle part of the horn (LD-ICI-MH, n=11 and SD-ICI-MH, n=20). Pregnancy rates after LD-ICI-UTJ, LD-ICI-MH, SD-ICI-UTJ and SD-ICI-MH were 27%, 27%, 39% and 35%, respectively (P>0.05). The total pregnancy rate after LD-ICI (27%) did not differ (P>0.05) from that after SD-ICI (37%) or SD-AI (34%). In Experiment 2 (field trial), 362 cows were allotted, at spontaneous estrus, to LD-ICI-UTJ (n=86), LD-ICI-MH (n=97) or SD-AI (n=179). Pregnancy rates after LD-ICI and SD-AI were 47% and 45%, respectively (P>0.05). After LD-ICI-UTJ, the pregnancy rate (54%) did not differ significantly (P>0.05) to that obtained after LD-ICI-MH (41%) and after SD-AI (45%). The results of the study show that the single intracornual insemination of cows with 2 x 10(6) spermatozoa at fixed time, 80-82 h after the second PGF(2)alpha injection or at spontaneous estrus resulted in similar pregnancy percentage as intracornual and conventional inseminations with 40 x 10(6) spermatozoa per semen dose. With intracornual insemination using low or standard dose of spermatozoa, the pregnancy rates were not significantly affected by the exact site of semen deposition in the uterine horn, near the utero-tubal junction or in the middle part.     

Effect of timing of artificial insemination on gender ratio in beef cattle

It was recently reported that cows inseminated at approximately 10 or 20 h before an expected ovulation deliver predominately a bull or heifer calf, respectively. The objective of this study was to further investigate the effect of timing of insemination on the gender of offspring in cattle. Angus heifers (n = 41) and cows (n = 98) were used in the study. Heifers were synchronized with a 16-d treatment of melengestrol acetate followed 17 d later with an injection of PGF2alpha. Cows were synchronized with GnRH followed 7 d later with PGF2alpha. A HeatWatch electronic estrus detection system was used to determine the onset of estrus. Based on previous studies, it was assumed that ovulation occurs approximately 32 h after the onset of estrus. Therefore, animals were artificially inseminated at either 8 to 10 h (early; > or = 20 h before expected ovulation) or 20 to 25 h (late; < or = 10 h before expected ovulation) after the onset of estrus. Sixty to 80 d after insemination, ultrasonography was used to confirm pregnancy status and to determine the gender of fetuses. Gender of calves was subsequently confirmed at calving. Data were analyzed for effects of time of insemination and sire or semen batch on gender ratio, as well as any effect of length and/or intensity of estrus on conception rate and gender ratio. Twenty-nine of 41 heifers and 69 of 98 cows were detected in estrus after synchronization and were inseminated; 20 of 29 heifers and 48 of 69 cows were subsequently confirmed pregnant. Neither the length of estrus nor its intensity (number of mounts) had an effect on pregnancy rate or gender ratio (P > or = 0.418). Timing of insemination (early versus late) had no effect on gender ratio (P = 0.887). Semen from 13 sires representing 17 lots was used to inseminate the cows and heifers. No differences (P = 0.494) were detected in the gender ratios resulting from different sires or semen batches. In contrast to previous findings, our results indicate that inseminating beef cattle at approximately 20 or 10 h before an expected ovulation does not alter the gender ratio of the resultant calves.     

Laparoscopic insemination technique with low numbers of spermatozoa in superovulated prepuberal gilts for biotechnological application

New biotechnologies, such as sperm-mediated gene transfer (SMGT), spermatozoa freezing and spermatozoa sorting have improved the possibilities to produce animals with desirable features. The main problem associated with these technologies is the scarce availability of spermatozoa for insemination. The objective of this study was to develop a laparoscopic insemination (LI) technique in gilt that allows the use of low semen doses resulting in high fertilization rates (FR) and minimal distress to the animal; the efficiency of this technique was compared to conventional artificial insemination (AI). Ten gilts were inseminated 36 h post hCG treatment near both utero-tubal junctions (UTJ) with 1.5 x 10(9)spermatozoa/5 mL per horn and 10 gilts (C) underwent conventional AI. Embryos were collected either at two to four cell stage (LI, n = 5; C, n = 5) for determination of fertilization rate or at day 6 for evaluation of developmental competence (LI, n = 5; C, n = 5). LI gilts showed a slightly higher FR than control animals. In a second trial, 24 gilts underwent LI with varying doses (1.5 x 10(8), 1.5 x 10(7), 1 x 10(7), 5 x 10(6) or 1 x 10(6)) of semen. Two to four stage embryos were collected and FR was evaluated in each tube. FR obtained with the lowest dose was significantly different from that with other dosages (P < 0.05). Embryos were cultured in vitro to blastocyst stages (percentage of blastocysts: 79.2 +/- 3.6%). In a third trial, five gilts were inseminated with semen processed by SMGT technique; both FR (86.1 +/- 9.9%) and transgene protein expression were satisfactory. In conclusion, this study shows that LI can be a useful tool for reducing doses of insemination, without affecting the efficiency of fertilization; this technique could have a wide range of biotechnological applications.     

Management of reproduction in dairy heifers based on the synchronization of estrous cycles

Israeli-Holstein breed dairy heifers (n = 571), 13 to 15 mo old, were utilized in two experiments. In Experiment 1, the reproductive performance of synchronized heifers was compared with that of untreated controls. The heifers in both groups were inseminated following the detection of estrus. In Experiment 2, all heifers were synchronized and inseminated following the detection of estrus. Half of the animals in this experiment also received one or two fixed-time inseminations 72 and 96 h after the last synchronization treatment. Synchronization of estrous cycles was performed by two prostaglandin F(2alpha) (PG) injections given 12 d apart. In the control group of Experiment 1, observation of estrous behavior and insemination of heifers detected in estrus were carried out daily throughout the experiment. In the synchronized groups of Experiments 1 and in 2, the management of reproduction consisted of estrus detection followed by the insemination of heifers in estrus carried out only during 6 d of every 3 wk. Five days following the second PG injection, 86% of the heifers were detected in estrus, 71% of them at 49 to 96 h after treatment. In Experiment 1, age at first insemination, age at conception, and conception rate were, respectively, 425 d, 446 d and 54% in the control group vs 432 d (P<0.02), 449 d and 62% in the PG-treated group. In Experiment 2, the respective figures were 436 d, 462 d and 59% in the group inseminated following the detection of estrus vs 427 d (P<0.002), 464 d and 51% (P<0.05) in the group in which heifers were inseminated at estrus and also received one or two fixed-time inseminations.     

Reproductive performance of high growth rate gilts inseminated at an early age

The aim of this work was to determine if gilts, which have a high growth rate (GR) could be mated earlier without reducing the reproductive performance or increasing the culling rate up to the third parity. Gilts of Camborough 22 (C22, n=568) breeding were mated and allocated into three groups according to weight and age on the insemination day. G1 (n=164)-gilts with a GR>or=700 g/d and inseminated at <210 d. G2 (n=165)-gilts with a GR>or=700 g/d and inseminated at >or=210 d. G3 (n=239)-gilts with a GR<700 g/d and inseminated at >or=210 d. All females were fed ad libitum from 150 d on and were inseminated at their second estrus or later. The minimum weight at mating was 127 kg. Three parities were studied, with farrowing rate, litter size and culling rate being compared. At the first parity, G2 gilts produced, on average, one more piglet than the other groups (P<0.05). However, when analyzing three parities, there were no differences in total born (11.6 x 12.3 x 11.7), farrowing rate (87.1% x 88.7% x 89.8%) and culling rate (30.2% x 25.3% x 28.2%) among G1-G3 groups, respectively (P>0.05). In conclusion, gilts, which had a minimum weight of 127 kg can be inseminated at their second or greater estrus, between 185 and <210 d of age, without impairing their productive performance over three parities.     

Cytogenetic analysis of Day-4 embryos from PMSG/hCG-treated prepuberal gilts

Prepuberal gilts were treated with pregnant mare serum gonadotropin (PMSG) to study the effects of its dosage on ovulation rate, fertilization rate after artificial insemination, embryo viability, and rate of development and incidence of chromosome abnormalities in Day-4 embryos. Gilts received 750 IU, 1250 IU or 1500 IU of PMSG, followed 72 h later by 500 IU human chorionic gonadotropin (hCG). Gilts were inseminated 28 to 30 h following the hCG injection, and resulting embryos were collected on Day 4 post ovulation. Ovulation rate was higher in the 1250 IU group than in the 1500 IU group or the 750 IU group. The 1500 IU dose caused excessive stimulation of the ovary, resulting in the occurrence of large (>10mm diameter) unovulated follicles, reduced fertilization rate and low embryo recovery rate. There was no difference in the incidence of chromosome abnormalities among the three groups, although the 1500 IU group had higher embryonic mortality than the two lower dose groups. A dose of 1250 IU PMSG increased ovulation rate above that achieved by 750 IU and, therefore, increased the number of oocytes or embryos available for transfer or for other studies, without sacrificing embryo viability or increasing the incidence of chromosome abnormalities.     

A field investigation of intra-cervical insemination with reduced sperm numbers in gilts

A novel insemination catheter with a smaller polyurethane tip for deeper insertion into the cervix of gilts was compared with the conventional catheter. The novel catheter could be inserted 31.4 mm deeper than the conventional catheter into the gilt cervix, but the difference diminished with parity until the sixth parity when there was no difference in penetration depth between the catheters. In Experiment 1, cyclic gilts were inseminated upon display of oestrus (back pressure test) in the presence of a boar (0 h) and 24 h later. The control group (n = 300) were inseminated with 2 x 10(9) total spermatozoa and the treatment group (n = 300) with 1 x 10(9) total spermatozoa per inseminate, in both cases utilising the novel insemination catheter. No significant differences were observed for farrowing rate and litter size, the values of which were those expected for natural mating. In Experiment 2, 66 cyclic gilts were subjected to the same heat detection and service regime as for Experiment 1 but were served with <1 x 10(9) total sperm cells per inseminate using the new device. Conception rates and embryo counts were recorded. Conception rate declined with <500 x 10(6) spermatozoa, and number of embryos (a reflection of potential litter size) was significantly reduced. Use of the new catheter for gilts with 1 x 10(9) total sperm cells per inseminate will achieve commercially acceptable fertility and fecundity levels, and offer substantial commercial benefits with more rapid genetic gains.