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PubMed1980

Distribution of small- and medium-sized molecules within the genital tract of artificially inseminated gilts.

Radiolabelled compounds of different molecular size were used as tracers mixed with seminal plasma to investigate whether seminal plasma enters the oviducts of inseminated gilts. The substances were 125I-labelled human serum albumin for 3 gilts, 131I-labelled polyvinylpyrrolidone plus 59Fe citrate in 2 gilts and 131I-labelled human serum albumin plus 59Fe citrate in 2 gilts. The gilts were slaughtered 1 h after insemination and the radioactivity was measured in 4 parts of the oviduct, 9 parts of the uterine horns, the body of the uterus and the cervix. Different quantities of the compounds used were found in all oviducts, but there was close agreement between the distributions of the two compounds in the genital tract after simultaneous insemination. There was a difference (60-80%) in total amount of recovered radioactivity between left and right uterine horns. It is concluded that all compounds used entered the oviducts regardless of their molecular sizes.

Animals↗
PubMed1988

Hormonal and behavioural detection of oestrus in blackbuck, Antilope cervicapra, and successful artificial insemination with fresh and frozen semen.

Hormonal detection of urinary pregnanediol-3 alpha-glucuronide proved an effective method of monitoring the progress of oestrous cycles in the blackbuck; observation of sexual behaviour in a vasectomized male was, however, a more practical procedure. Good correlation was observed between the occurrence of minimal pregnanediol concentrations in females and the maximal behavioural response by the male. On the basis of intervals between periods of behaviourally detected oestrus, a mean cycle length of 16.9 days (+/- 0.62, s.e.m.) was derived from 12 cycles (4 animals). Eleven females were inseminated in this study, 8 with freshly collected semen and 3 with frozen semen; 6 calves were obtained, 1 after the use of frozen semen. Pregnancy was monitored by measurements of pregnanediol-3 alpha-glucuronide excretion and by ultrasound scanning. The mean interval between insemination and parturition was 183.3 days inclusive, ranging from 182 to 186 days.

Animals↗
PubMed1988

Turkey hen fertility and egg production after artificial insemination and multiple oviduct eversion during the pre-laying period.

The onset of egg production (mean 18.3 days after the onset of photostimulation) and the rate of egg production (flock averaged 4.9 eggs per bird per week for the first 8 weeks of egg production) were not affected by 5 days of twice daily oviduct eversion ('venting') in the pre-laying period when compared to unvented controls. After the onset of photostimulation, pre-laying hens were inseminated twice daily on Days 12 to 16 with 3 microliter semen containing 15 x 10(6) spermatozoa, and compared with groups of hens inseminated once daily on Days 15 and 16 with 15 microliters semen containing 75 x 10(6) spermatozoa or 41 microliter semen containing 200 x 10(6) spermatozoa. Fertility remained high for the first 5 weeks of egg production. However, by Week 6 the fertility of the hens receiving frequent low doses of semen dropped significantly below that of the others, which suggests that multiple inseminations with a low semen volume containing relatively low numbers of spermatozoa does not lead to an increase in the efficacy of sperm transport and storage in the oviduct.

Animals↗
PubMed1991

Artificial insemination of red deer (Cervus elaphus) with frozen-thawed wapiti semen.

Semen collected from wapiti (Cervus elaphus) in Canada in 1983 was frozen in two extenders. In 1988, the semen was used to inseminate 200 red deer hinds on 2 farms in New Zealand. Oestrus was synchronized in the hinds with progesterone-impregnated intravaginal devices (CIDR); 200 iu pregnant mares' serum gonadotrophin was given to each hind on Day 11. The CIDRs were removed on Day 12 at 20/h, as the numbers of the hinds were recorded. On Day 14, 54-56 h after CIDR removal, the hinds were brought into the yards in the same batches and laparoscopically inseminated. Semen from three sires was used. The overall conception rate was 51%. Gestation length ranged from 239 to 247 days. One hind was lost at calving, 3 calves had to be hand raised and there were 2 neonatal calf deaths.

Animals↗
PubMed1994

Superovulation in red deer (Cervus elaphus) and Père David's deer (Elaphurus davidianus), and fertilization rates following artificial insemination with Père David's deer semen.

Two comparative studies were undertaken using adult, female red and Père David's deer to examine the ovulatory response of these animals to a superovulation regimen and fertilization rates following inter- and intraspecific laparoscopic insemination. In Expt 1 six Père David's deer and 12 red deer hinds were treated during the breeding season with an intravaginal progesterone-impregnated controlled internal drug release device (CIDR) for 14 days, with 200 iu pregnant mares' serum gonadotrophin (PMSG) administered 72 h before the device was withdrawn and eight injections of ovine FSH given at 12 h intervals starting at the time of PMSG administration. Oestrous behaviour began one day after CIDR device withdrawal (Père David's deer: 24.00 +/- 2.32 h; red deer: 24.60 +/- 2.23 h). The duration of oestrus was greater in Père David's deer than in red deer (17.50 +/- 1.43 h and 8.25 +/- 3.25 h, respectively, P < 0.001). The peak LH surge of Père David's deer was 68.65 +/- 4.74 ng ml-1 occurring 29.00 +/- 2.41 h after removal of the CIDR devices. In comparison, the peak LH surge in red deer was 17.09 +/- 3.64 ng ml-1 (P < 0.001), occurring 24.00 +/- 0.00 h after CIDR device withdrawal. Pre-surge concentrations of LH were also greater (P < 0.001) in Père David's deer (1.37 +/- 0.11 ng ml-1) than in red deer hinds (0.41 +/- 0.02 ng ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Responsiveness of ovaries to exogenous gonadotrophins and laparoscopic artificial insemination with frozen-thawed spermatozoa in ocelots (Felis pardalis).

Adult female ocelots (Felis pardalis) were treated with one of four dosages of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) (100 iu eCG/75 iu hCG, n = 3; 200 iu eCG/150 iu hCG, n = 4; 400 iu eCG/150 iu hCG, n = 5; 500 iu eCG/225 iu hCG, n = 5); hCG was administered 80 h after eCG. Ovaries of each animal were evaluated by laparoscopy 39-43 h after hCG, and blood was collected for progesterone and oestradiol analysis. With progressive increases in gonadotrophin dosage, female ocelots produced more (P < 0.05) unovulated follicles (> or = 2 mm in diameter), ranging from 1.3 +/- 0.7 (mean +/- SEM) follicles per female at the lowest dosage to 8.8 +/- 2.8 follicles per female at the highest dosage. Similarly, ocelots produced more (P < 0.05) corpora lutea with increasing gonadotrophin dosages, with mean values ranging from 0-5.0 +/- 1.2 corpora lutea. However, across treatment groups, a similar proportion (P > 0.05) of females ovulated in response to each dosage. At laparoscopy, serum concentrations of oestradiol (overall mean, 330.2 +/- 62.2 pg ml-1) and serum concentrations of progesterone (overall mean, 18.5 +/- 6.4 ng ml-1) in ovulating females did not differ (P > 0.05) across treatment groups. Ten ovulating ocelots were laparoscopically inseminated with fresh (4.7 +/- 0.2 x 10(6); n = 2 females) or frozen-thawed (10.7 +/- 1.8 x 10(6); n = 8 females), motile spermatozoa. One female treated with 500 iu eCG/225 iu hCG and inseminated with 7.5 x 10(6) motile, frozen-thawed spermatozoa conceived and gave birth to a healthy male kitten after a gestation of 78 days. We conclude that ocelots are relatively insensitive to exogenous gonadotrophins, requiring much higher dosages (on a per body mass basis) to elicit an appropriate ovarian response than do any other felid species studied to date. Nonetheless, the gonadotrophin-treated female can become pregnant and carry offspring to term after laparoscopic intrauterine insemination with frozen-thawed spermatozoa.

Animals↗
PubMed2004

The invisible man. Artificial insemination by donor and the legislation on donor anonymity: a review.

Until recently, sperm donors have remained anonymous under the 1990 Human Fertilisation and Embryology Act. There has been a distinct international trend towards allowing children access to identifying information about their donor. The UK has followed and, subject to parliamentary approval, children born by donations made after 1 April 2005 will be legally entitled to information revealing the identity of their donor. The lifelong well-being of the child created must be the prime consideration in any reform of the law.

Access to Information↗
PubMed1992

Accessory sperm: their importance to fertility and embryo quality, and attempts to alter their numbers in artificially inseminated cattle.

Accessory sperm number and its relationship to fertilization and embryo quality was evaluated in cattle after nonsurgical recovery of ova or embryos 6 d after insemination. Efforts to alter accessory sperm number per ovum included 1) blockage of retrograde sperm loss at insemination using a modified insemination device, 2) elevated sperm number per inseminate (40 x 10(6) vs 20 x 10(6], and 3) alteration in semen quality (percentage of viable and morphologically normal sperm in the inseminate). None of these efforts affected accessory sperm number per ovum or embryo. However, blockage of retrograde semen flow for 3 h or use of semen of below-average quality (decreased percentage of viable and morphologically normal sperm) resulted in significant decreases in number of viable embryos and increases in number of degenerate embryos and unfertilized ova compared with conventional insemination (P less than .03) and use of semen with an average percentage of viable and morphologically normal sperm (P less than .06). Number of accessory sperm per embryo or ovum was positively related to fertilization and embryo quality (P less than .05). Mean accessory sperm +/- SD and the median value (in parentheses) for unfertilized ova, degenerate embryos, and embryos classified fair to poor and excellent to good were, respectively, .3 +/- .8 (0), 5.4 +/- 8.9 (1.0), 15.8 +/- 28.6 (3.5), and 16.9 +/- 29.5 (5.0). We conclude that efforts to improve accessory sperm numbers per embryo or ovum failed and that high variation and skewness of accessory sperm toward 0 may make median values more meaningful than means.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Reproductive performance and estimates of labor requirements associated with combinations of artificial insemination and natural service in swine.

A study was conducted to examine effects of mating systems composed of natural service (NS) and AI in swine on farrowing rate, litter size, and labor requirements. Sows and gilts were bred once per day via one of the following treatments (d 1/d 2): NS/NS, NS/AI, AI/AI, and NS/none. Gilts bred with NS/AI, AI/AI, and NS/NS had higher (P less than .05) farrowing rates than gilts bred with NS/none matings. Similarly, farrowing rates were higher (P less than .05) in NS/AI than in NS/NS gilts. Numbers of pigs born alive were greater (P less than .05) in NS/NS, NS/AI, and AI/AI than in NS/none gilts. In sows, a treatment x time interaction (P less than .01) was present for farrowing rate. In the AI/AI treatment, farrowing rate increased (P less than .01) from 70.0% (wk 1 through 3) to 88.5% (wk 4 through 10). Farrowing rates were 87.3, 93.2, and 76.0% in the NS/NS, NS/AI, and NS/none groups, respectively, and did not change (P = .72) over time. Sows bred via NS/NS and NS/AI had larger litters (P less than .05) than NS/none sows. In the present study, if four or more sows and gilts were bred, then AI required less (P less than .05) time per animal than NS. Furthermore, gilts required more (P less than .05) time for breeding than sows. Results from this study demonstrate that gilts and sows responded differently to combinations of NS and AI in terms of reproductive performance. In addition, differences in labor requirements per sow or gilt between NS and AI matings were dependent on parity and daily breeding demands.

Age Factors↗
PubMed1993

Effect of freezing semen and dosage of sperm on number of accessory sperm, fertility, and embryo quality in artificially inseminated cattle.

This experiment was conducted to determine whether use of fresh or frozen semen at either 20 x 10(6) (low) or 100 x 10(6) (high) sperm per dose affects the number of accessory sperm and fertilization status/embryo quality as determined from ova/embryos recovered nonsurgically 6 d after insemination. Ejaculates of four bulls were split and prepared for use as fresh or frozen semen at either the high or low dose. From 129 inseminations to normally cycling cows, 98 ova/embryos were recovered. To reduce male effects, ova/embryos used were randomly balanced across treatments, by ejaculate within bull for evaluation of frozen vs fresh semen (n = 80) and by bull for evaluation of high vs low dosage treatments (n = 76). Distribution of accessory sperm was highly skewed downward; thus, median values were more meaningful than means. Freezing semen had no significant effect on fertility status/embryo quality or number of accessory sperm at either dosage. Increasing dosage improved the number of accessory sperm per ovum or embryo (median value) and fertility status/embryo quality (P < .05). Mean +/- SD and median values for accessory sperm were 37.8 +/- 38.3 and 27.5; 28.9 +/- 62.8 and 3.0 for the high and low dose, respectively. Percentage of unfertilized ova, degenerate embryos, and embryos classified poor to fair and good to excellent were 3, 5, 24, 68, and 21, 16, 18, 45, for the high and low dose, respectively. We conclude that number of accessory sperm and fertility status/embryo quality respond favorably to increased dosage of semen and that freezing semen in this study was not detrimental to these parameters.

Animals↗
PubMed2000

The importance of seminal plasma on the fertility of subsequent artificial inseminations in swine.

Yorkshire x Landrace sows and gilts were used in a 3x2 factorial arrangement of treatments to determine the effect of uterine inflammation induced by either killed spermatozoa (KS) or bacterial lipopolysaccharide (LPS) on the fertility of a subsequent, optimally timed AI. Estrus was detected with a mature boar twice daily. Twelve hours after the first detection of estrus, females received intrauterine infusions of an inflammatory stimulus consisting of a 100-mL dose of extender containing 3x10(9) KS (n = 40), 20 microg of LPS (n = 40; positive control) or extender alone (n = 40; negative control). An insemination was performed 12 to 18 h later with 3x10(9) motile spermatozoa (i.e., fertile AI) suspended in either 100 mL of seminal plasma (SP; n = 60) or extender replenished with of estrogens (5 microg of estradiol-17beta, 4.5 microg of estrone sulfate, and 2 microg of estrone; n= 60). Transcutaneous ultrasound was performed at the time of fertile AI and again 24 h later to detect the presence or absence of preovulatory follicles. A fertile AI performed within 24 h before ovulation was considered optimal. Conception (CR) and farrowing rates (FR) were greater in females that received a fertile AI diluted with SP compared with extender (P<.01), and there was a significant (P<.05) treatment x fertile AI dilution medium interaction for both CR and FR. Females that received a fertile AI 12 h after infusion of extender had similar CR and FR regardless of fertile AI dilution medium. After inducing an inflammatory response with either KS or LPS, CR and FR were higher in females that received a fertile AI diluted with SP compared with fertile AI dilution with extender (P<.05). The effects of treatment and AI dilution media and their interactions were not significant for litter size in females that farrowed. These results show that the fertility of a subsequent AI can be impaired when semen is deposited into an inflamed environment created by an earlier AI, and this impairment was offset by inclusion of SP in the subsequent insemination.

Animals↗
PubMed2001

Oxytocin-induced cervical dilation and cervical manipulation in sheep: effects on laparoscopic artificial insemination.

The difficulty of cervical penetration severely limits the use of transcervical AI (TAI) in sheep, and trauma from cervical manipulation (CM) may reduce fertility after TAI. We investigated the effects of cervical dilation using exogenous oxytocin (OT) to facilitate TAI and its effects on reproductive variables after laparoscopic AI (LAI). Estrus was synchronized by inserting pessaries impregnated with 6alpha-methyl-17alpha-hydroxyprogesterone acetate (60 mg) for 12 d. In Exp. 1, we determined whether OT and CM before LAI affected the interval from pessary removal to ovulation and fertilization rate. Crossbred ewes (n = 16) were assigned to 1) saline-CM or 2) OT-CM. In Exp. 2, effects of OT and CM on lambing rates were evaluated with white-faced ewes (n = 220) in a 2 x 2 factorial experiment: 1) saline-sham CM; 2) saline-CM; 3) OT-sham CM; and 4) OT-CM. In both studies, eCG (400 IU i.m.) was injected at pessary removal, and LAI was performed 48 to 52 h later. In Exp. 1, ewes received i.v. either 400 USP units of OT or 20 mL of saline at 30 to 60 min before LAI, and CM was administered as for TAI. Beginning 32 h after pessary removal and continuing at 8-h intervals, ovaries were examined with ultrasonography to estimate time of ovulation. Treatment in Exp. 1 did not affect combined ovum/embryo recovery rate (69%), but OT-CM decreased fertilization rate (47 vs 59%; P < 0.05). The OT tended to reduce the interval to ovulation (OT, 59 h vs saline, 66 h; P < 0.06). The OT x CM interaction in Exp. 1 was not significant. For Exp. 2, approximately 25 min before sham CM or CM, 200 USP units of OT or 10 mL of saline was injected i.v. The LAI was performed immediately after sham CM or CM. At 10 to 12 d after AI in Exp. 2, ewes were mated with Suffolk rams. Blood was collected between 24 and 26 d after AI for pregnancy-specific protein B (PSPB) RIA. The PSPB pregnancy and lambing rates were both 62% in saline-sham controls. The CM did not affect pregnancy (69%) or lambing rate (64%). The OT treatment decreased (P < 0.05) PSPB pregnancy (59%) and lambing rates (56%) in OT-sham ewes and pregnancy and lambing rates in CM ewes (both 43%). Neither CM nor OT before LAI affected lambing rates to next estrus, indicating no long-term damage to the cervix or uterus. In summary, CM did not affect fertility after LAI, but OT decreased lambing rate independent of CM. If OT will not be usable for TAI, it may still be a tool for training TAI personnel.

Animals↗
PubMed2003

Influence of hormone supplementation to extended semen on artificial insemination, uterine contractions, establishment of a sperm reservoir, and fertility in swine.

This study was performed to quantify the effect of hormone addition to semen using a low-fertility model to evaluate its effectiveness and mode of action. At 24 h after the onset of estrus, all gilts received a single low-dose AI (0.5 x 10(9) sperm/80 mL) with no hormone (control, C), estrogens (E, 11.5 microg), PGF2alpha (PG, 5 mg of Lutalyse), or oxytocin (OT, 4 IU), which were then evaluated for semen backflow (n = 48), oviductal and uterine sperm numbers (n = 28), uterine contractions (n = 12), pregnancy rate (PR, n = 120), and number of fetuses (n = 67). In Exp. 1, backflow of semen from the uterus was collected for 8 h after AI, whereas PR and fetuses were assessed at d 25 to 30 after AI. In Exp. 2, backflow was collected and reproductive tracts flushed to determine sperm numbers in the oviducts and the anterior segments of the uterus. In Exp. 3, sows were monitored for uterine contractions for 1 h before AI and for 2 h after AI. In Exp. 1, there was a treatment x time interaction for fluid loss (P < 0.001), but by 8 h after AI, there was no difference in the total volume (70 +/- 1 mL) of semen lost between hormone treatments (85%) compared to controls (90%). There was also a treatment x time interaction (P < 0.05) for number of sperm lost in the backflow (2.1 +/- 0.1 x 10(8)), but by 8 h following AI, there was no effect on total sperm lost for the hormone treatments (38%) compared to C (54%). There was a trend (P = 0.10) for increased numbers of sperm in the uteri of hormone-treated gilts (6.0 +/- 1.3 x 10(4)) compared with C gilts (2.2 +/- 1.3 x 10(4), but there was no effect of treatment on sperm numbers in the oviducts (3.2 +/- 1.3 x 10(4)). Within 0.5 h of AI, there was an increase in the frequency of contractions for PG compared with the other treatments (14.2 vs. 6.3/h, P < 0.005), however there was no effect on amplitude (54 mmHg) or duration (35 s) of contractions. The PR was not influenced by treatment and averaged 54% (P > 0.60), but total numbers of healthy fetuses were increased (P < 0.04) by PG (8.7) and tended (P = 0.06) to be increased for OT (8.4), but not for E (7.2) compared to C (5.8). Hormone addition to semen increased numbers of fetuses and this may be related to an alteration in the pattern of fluid and sperm loss after AI and a tendency for increased numbers of sperm in the anterior segment of the uterus. Therefore, in situations of lowered fertility, hormone addition could be a strategy to limit infertility in swine.

Animals↗
PubMed2004

Threshold-linear analysis of measures of fertility in artificial insemination data and days to calving in beef cattle.

Mating and calving records for 47,533 first-calf heifers in Australian Angus herds were used to examine the relationship between days to calving (DC) and two measures of fertility in AI data: 1) calving to first insemination (CFI) and 2) calving success (CS). Calving to first insemination and calving success were defined as binary traits. A threshold-linear Bayesian model was employed for both analyses: 1) DC and CFI and 2) DC and CS. Posterior means (SD) of additive covariance and corresponding genetic correlation between the DC and CFI were -0.62 d (0.19 d) and -0.66 (0.12), respectively. The corresponding point estimates between the DC and CS were -0.70 d (0.14 d) and -0.73 (0.06), respectively. These genetic correlations indicate a strong, negative relationship between DC and both measures of fertility in AI data. Selecting for animals with shorter DC intervals genetically will lead to correlated increases in both CS and CFI. Posterior means (SD) for additive and residual variance and heritability for DC for the DC-CFI analysis were 23.5 d2 (4.1 d2), 363.2 d2 (4.8 d2), and 0.06 (0.01), respectively. The corresponding parameter estimates for the DC-CS analysis were very similar. Posterior means (SD) for additive, herd-year and service sire variance and heritability for CFI were 0.04 (0.01), 0.06 (0.06), 0.14 (0.16), and 0.03 (0.01), respectively. Posterior means (SD) for additive, herd-year, and service sire variance and heritability for CS were 0.04 (0.01), 0.07 (0.07), 0.14 (0.16), and 0.03 (0.01), respectively. The similarity of the parameter estimates for CFI and CS suggest that either trait could be used as a measure of fertility in AI data. However, the definition of CFI allows the identification of animals that not only record a calving event, but calve to their first insemination, and the value of this trait would be even greater in a more complete dataset than that used in this study. The magnitude of the correlations between DC and CS-CFI suggest that it may be possible to use a multitrait approach in the evaluation of AI and natural service data, and to report one genetic value that could be used for selection purposes.

Animals↗
PubMed2006

Conception rates to artificial insemination in primiparous, suckled cows exposed to the biostimulatory effect of bulls before and during a gonadotropin-releasing hormone-based estrus synchronization protocol.

The objective of these studies was to evaluate whether exposing primiparous, suckled beef cows to the biostimulatory effect of bulls alters breeding performance associated with an estrus synchronization protocol that included GnRH followed 7 d later by PGF(2alpha) and fixed-time AI (TAI). This was a composite analysis of 3 experiments that evaluated (1) the effects of bull exposure at different days after calving (yr 1); (2) the biostimulatory effects of bull excretory products (yr 2); and (3) the biostimulatory effects of familiar and unfamiliar bulls (yr 3) on the resumption of ovarian cycling activity. In all studies, cows were exposed (biostimulated; n = 94) or not exposed (nonbiostimulated; n = 67) to bulls or excretory products of bulls for at least 60 d before the beginning of the estrus synchronization protocol. Average calving day did not differ among years and was 52 +/- 5 d. Year did not affect the proportions of biostimulated and nonbiostimulated cows that were cycling at the beginning of the estrus synchronization protocol; however, a greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows were cycling at this time. In each year, cows were given GnRH followed by PGF(2alpha) 7 d later. Cows were observed for estrus twice daily (am and pm) after PGF(2alpha). Cows that exhibited estrus before 54, 60, and 64 h after PGF(2alpha) were inseminated by AI 12 h later in yr 1, 2, and 3, respectively. Cows that failed to show estrus were given GnRH and TAI at 62, 72, and 72 h after PGF(2alpha) in yr 1, 2, and 3, respectively. Conception rates were determined by transrectal ultrasonography 35 d after TAI in each year. The percentages of cows that exhibited estrus after PGF(2alpha) and before TAI, the interval from PGF(2alpha) to estrus, and the percentages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows and were 51%, 54.7 +/- 7.3 h, 35%, and 65%, respectively. Conception rates for cows bred by AI 12 h after estrus did not differ between biostimulated and nonbiostimulated cows; however, the TAI conception rate was greater (P < 0.05) for biostimulated cows (57.6%) than for nonbiostimulated cows (35.6%). We conclude that TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF(2alpha) may be improved by the biostimulatory effect of bulls in postpartum, primiparous cows.

Animals↗
PubMed2006

Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone.

We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F2alpha (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 microg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 microg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 microg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.

Animals↗