Two experiments tested the efficacy of gonadotropin-releasing hormone (GnRH) or estradiol cypionate (ECP) administration in combination with controlled internal drug release (CIDR) inserts on pregnancy rate to fixed-time artificial insemination (FTAI) in beef heifers. In the first experiment, heifers in the two ECP groups received ECP in conjunction with the CIDR insert. The CIDR insert was removed and PGF was administered on either d 7 or 9. Heifers received ECP 24 h after CIDR removal and were inseminated 30 h after ECP. Heifers in the two GnRH groups received GnRH in conjunction with the CIDR insert. Heifers received PGF on either d 6 or 7, and the CIDR insert was removed on d 7. Heifers were inseminated and received GnRH 48 h after CIDR removal. Pregnancy rates to FTAI were higher for heifers treated with GnRH. Pregnancy rate to FTAI was highest for heifers in the GnRH group that received PGF on d 6 and was lowest for the group that received ECP in combination with a 7-d CIDR insert. In the second experiment, heifers received GnRH in conjunction with the CIDR insert. CIDR inserts were removed and PGF was administered on d 7. Heifers were inseminated 60 h later, with one group receiving GnRH at insemination. Pregnancy rate to FTAI was higher for heifers that received GnRH at insemination. The final experiment tested the efficacy of estradiol 17_ (E17) or GnRH in combination with a CIDR insert on pregnancy rate to FTAI in Brahman cows. Either E17 or GnRH was administered in conjunction with the CIDR insert. CIDR inserts were removed on d 7. Cows in the GnRH group received PGF on d 6 and GnRH at insemination which occurred 48 h after CIDR removal. Cows in the E17 group received PGF on d 7, E17 24 h later, and were inseminated 30 h after E17 administration. Pregnancy rate to FTAI was higher for cows treated with E17. These data indicate acceptable pregnancy rates were obtained when the CIDR insert was combined with either GnRH in beef heifers or with E17 in Brahman cows.

Master of Science / Department of Animal Sciences and Industry / Karol E. Fike / David M. Grieger / Synchronizing estrus before AI is an effective way to shorten the breeding season, and increasing the number of pregnancies per AI may lead to greater use and acceptance of synchronization protocols among beef producers. Our objective was to determine if pregnancy rates to fixed-time AI (FTAI) would be improved by delaying insemination in heifers not expressing estrus before FTAI in a 7-d CO-Synch + controlled internal drug release (CIDR) estrus-synchronization protocol. In Experiment 1, yearling beef heifers (n = 465) at three locations of commercial and purebred herds were treated with GnRH (Cystorelin 100 µg im) and a CIDR insert (1.38 g of progesterone) on Day 0. On Day 7 CIDR inserts were removed and all heifers received PGF[subscript]2α (Lutalyse 25 mg im) and were fitted with an estrus-detection patch (Estrotect; Rockway, Inc.). Heifers were assigned to three treatments based on estrus-detection patch color at 48 h after PGF[subscript]2α: (1). Estrus-Red 48 h (Red 48; n = 180), heifers that expressed estrus and were inseminated at 48 h; (2). Non-Estrus-Gray 48 h (Gray 48; n = 137) heifers that did not express estrus and were inseminated at 48 h; and (3). Non-Estrus Delayed- 56 h (Gray 56; n = 148), heifers that did not express estrus at 48 h, and were not inseminated until 56 h after PGF[subscript]2α. Pregnancy rate to AI was greatest (P < 0.0001) for Red 48 heifers (67.8%) compared with heifers in the Gray 48 (39.4%) and Gray 56 (42.6%) treatments. Heifers assigned to Gray 48 and Gray 56 achieved similar (P = 0.83) pregnancy rates. In Experiment 2, yearling beef heifers (n = 257) at two different locations were treated with the same 7-d CO-Synch protocol, but heifers were assigned to three different treatments based on estrus-detection patch color at 48 h after PGF[subscript]2α: (1). Estrus-Red 48 h (Red 48; n =95), heifers that expressed estrus and were inseminated at 48 h; (2). Non-Estrus-Gray 48 h (Gray 48; n = 84), heifers that did not express estrus but were inseminated at 48 h; and (3). Non-Estrus Delayed- 72 h (Gray 72; n = 78), heifers that did not express estrus at 48 h, and were not inseminated until 72 h after PGF[subscript]2α. Pregnancy rate to AI was greatest (P = 0.004) for Red 48 heifers (62.1%) compared with heifers in Gray 48 (40.5%), and Gray 72 (46.2%). No difference in pregnancy rates (P = 0.75) was detected between heifers assigned to treatments Gray 48 and Gray 72. Delaying insemination in heifers not expressing estrus by 48 h after PGF[subscript]2α did not improve pregnancy rates to AI.

A series of studies were guided by the principal hypothesis that it was necessary to characterize ovarian function during the seasons of the annual reproductive cycle in wapiti and that from this knowledge novel methods of exogenous control of ovarian function would be possible. To augment existing knowledge about endogenous control of ovarian function in wapiti studies were conducted to characterize ovarian follicle dynamics during the estrous season and to characterize ovarian follicular dynamics during the periods of transition into and out of the breeding season. The third study was designed to characterize ovarian follicle development and ovulation synchrony subsequent to an estrous synchronization protocol used commercially. To evaluate novel methods of exogenous control of ovarian function studies were conducted to determine if follicular wave emergence could be electively induced using hormonal or surgical treatments to evaluate novel ovarian superstimulatory treatment protocols. <p>It was concluded from the studies of ovarian function that follicle development during the breeding season was characterized by the regular and synchronous development of follicular waves and that 2, 3, or 4 waves occurred during each interovulatory interval. Transition into the breeding season was preceded by one short interovulatory interval (9 days) characterized by one wave of follicle development and a small, short-lived and hypo-functional corpus luteum. The last estrous cycle of the breeding season was similar to estrous cycles during the rut (21 days), but and transition to anestrus was marked by a failure of the dominant follicle to ovulate after luteal regression. The treatment protocol used commercially for estrous synchronization was effective, but unnecessarily long. It was concluded from the studies on exogenous control of ovarian function that follicular wave emergence could be electively induced using steroid hormones or follicle ablation and may be useful for estrus synchronization and superstimulatory protocols. The tested superstimulatory treatments were effective and had the advantage of reducing the treatment period by 6 days and the number of times the animals are handled by one third over a more conventional method. However, oocyte and embryo quality were not evaluated. <p>As a result of the studies conducted and one previous study during the anouvlatory season follicle and luteal dynamics are now known in wapiti for all seasons of the year and this knowledge will provide a template upon which other species of deer can be compared. The final two studies support the principal hypothesis. The novel methods of exogenous ovarian control tested increase the potential for success when applying reproductive technologies and the successful application of these methods in wapiti should lead to their successful use in other species of deer.

A series of studies were guided by the principal hypothesis that it was necessary to characterize ovarian function during the seasons of the annual reproductive cycle in wapiti and that from this knowledge novel methods of exogenous control of ovarian function would be possible. To augment existing knowledge about endogenous control of ovarian function in wapiti studies were conducted to characterize ovarian follicle dynamics during the estrous season and to characterize ovarian follicular dynamics during the periods of transition into and out of the breeding season. The third study was designed to characterize ovarian follicle development and ovulation synchrony subsequent to an estrous synchronization protocol used commercially. To evaluate novel methods of exogenous control of ovarian function studies were conducted to determine if follicular wave emergence could be electively induced using hormonal or surgical treatments to evaluate novel ovarian superstimulatory treatment protocols. <p>It was concluded from the studies of ovarian function that follicle development during the breeding season was characterized by the regular and synchronous development of follicular waves and that 2, 3, or 4 waves occurred during each interovulatory interval. Transition into the breeding season was preceded by one short interovulatory interval (9 days) characterized by one wave of follicle development and a small, short-lived and hypo-functional corpus luteum. The last estrous cycle of the breeding season was similar to estrous cycles during the rut (21 days), but and transition to anestrus was marked by a failure of the dominant follicle to ovulate after luteal regression. The treatment protocol used commercially for estrous synchronization was effective, but unnecessarily long. It was concluded from the studies on exogenous control of ovarian function that follicular wave emergence could be electively induced using steroid hormones or follicle ablation and may be useful for estrus synchronization and superstimulatory protocols. The tested superstimulatory treatments were effective and had the advantage of reducing the treatment period by 6 days and the number of times the animals are handled by one third over a more conventional method. However, oocyte and embryo quality were not evaluated. <p>As a result of the studies conducted and one previous study during the anouvlatory season follicle and luteal dynamics are now known in wapiti for all seasons of the year and this knowledge will provide a template upon which other species of deer can be compared. The final two studies support the principal hypothesis. The novel methods of exogenous ovarian control tested increase the potential for success when applying reproductive technologies and the successful application of these methods in wapiti should lead to their successful use in other species of deer.

Master of Science / Department of Animal Science and Industry / David M. Grieger / Controlling reproductive cycles during active cyclicity and seasonal anestrous in small ruminants is critical for profitability. The objective of this study was to evaluate the effect on estrous response and interval to estrus of two CIDR protocols in sheep and goats during breeding and non-breeding seasons. In experiment 1, 133 ewes were randomly assigned to 1 of 3 treatments during the breeding season. In the CIDR-7 group, ewes received a CIDR insert for 7 d. In the CIDR-7 + PGF treatment, ewes received a CIDR insert for 7 d and 20 mg of prostaglandin-F[subscript]2[subscript]α (PGF[subscript]2[subscript]α) upon CIDR removal. Ewes in the CIDR-14 treatment received a CIDR insert for 14 d. Following CIDR removal all ewes were exposed to a ram every 12 h until breeding. There was a shorter interval from CIDR removal to estrus in the CIDR-14 treatment compared to the CIDR-7 and CIDR-7 + PGF treatments (P<0.05). There was no difference in number of ewes per treatment displaying estrus. In experiment 2, 54 ewes were randomly assigned to one of two treatment groups during the anestrous season. Ewes in CIDR-7 and CIDR-14 treatments received a CIDR insert for 7 d and 14 d, respectively. Upon CIDR removal ewes were exposed to a ram every 12 h until breeding. There was a significantly shorter interval from CIDR removal to estrus in CIDR-14 ewes when compared with CIDR-7 ewes (P<0.05). For experiment 3, 37 Boer does were randomly assigned to one of two treatments. In the CIDR-10 treatment, does received a CIDR insert for 10 d and 20 mg of PGF[subscript]2[subscript]α at time of CIDR removal. In the CIDR-19 treatment, does received a CIDR insert for 19 d. Upon CIDR removal, does were exposed to a buck fitted with a marking harness and chalk marks were recorded every 12 h. The number of does displaying estrus was not different (CIDR-7, 85%; CIDR-14, 95%). There was no difference in interval from CIDR removal to estrus between treatments. Results from experiments 1 and 2 supported the hypothesis that long-term protocols yield a shorter interval to estrus when compared with short-term protocols.

Two studies were designed to characterize the effects of a non-steroidal aromatase inhibitor, letrozole, on ovarian function in cattle. The specific objective was to test the hypothesis that letrozole will arrest dominant follicle growth resulting in emergence of a new follicular wave at a predictable interval post-treatment. In a first experiment, postpubertal beef heifers were assigned randomly to four treatment groups and given phosphate-buffered saline (controls; n=10), or letrozole at a dose of 500 (n=9), 250 (n=10), or 125 (n=10) µg/kg intravenously 4 days after follicular ablation (~2.5 days after wave emergence). In a second study, postpubertal beef heifers were assigned randomly to four treatment groups. One group received no treatment (control; n=17) and the other groups (n=9-10) were given 85 µg/kg of letrozole per day (250 µg/kg total dose), from Days 1 to 3, Days 3 to 5, or Days 5 to 7 (Day 0 = pre-treatment ovulation,) corresponding to the periods before, during and after selection of the dominant follicle, respectively. Follicular dynamics were monitored ultrasonically and blood samples were collected for endocrine assays. Follicle diameter profiles and plasma LH, FSH, and estradiol concentrations were analyzed. Additionally, during the second trial, CL diameter profiles and plasma progesterone concentrations were measured. In both studies, the diameter profile of the dominant follicle was larger in heifers treated with letrozole than in control heifers (P<0.05) and the intervals to new wave emergence and onset of regression of the extant dominant follicle were longer (P<0.05) in heifers treated with letrozole than in controls, regardless of the dose (high, medium, or low; single vs multiple) and the stage of the follicle wave in which treatments were initiated. Furthermore, during the second experiment, the mean CL diameter was larger in letrozole-treated heifers, although there were no differences in plasma progesterone concentrations between treated and control animals. The effects on dominant follicle and CL diameter profiles appeared to be the result of the significantly increased plasma LH concentrations observed in letrozole-treated animals during both treatment approaches (single vs multiple dose). Incomplete and inconsistent inhibition of estradiol production and the lack of a surge on FSH observed in both experiments may be a result of insufficient circulating levels of letrozole during the treatment period. In summary, a single or multiple dose of letrozole did not induce regression of the extant dominant follicle, nor did it directly affect FSH release. Conversely, letrozole extended the lifespan of the dominant follicle, in association with increased endogenous levels of LH, thereby delaying the next FSH surge and subsequent follicular wave emergence. Results suggest that letrozole has potential as a non-steroidal method for controlling ovarian function in cattle, but further studies are warranted to clarify dosage and timing of treatment to predictably affect follicular wave dynamics in cattle.

Two studies were designed to characterize the effects of a non-steroidal aromatase inhibitor, letrozole, on ovarian function in cattle. The specific objective was to test the hypothesis that letrozole will arrest dominant follicle growth resulting in emergence of a new follicular wave at a predictable interval post-treatment. In a first experiment, postpubertal beef heifers were assigned randomly to four treatment groups and given phosphate-buffered saline (controls; n=10), or letrozole at a dose of 500 (n=9), 250 (n=10), or 125 (n=10) µg/kg intravenously 4 days after follicular ablation (~2.5 days after wave emergence). In a second study, postpubertal beef heifers were assigned randomly to four treatment groups. One group received no treatment (control; n=17) and the other groups (n=9-10) were given 85 µg/kg of letrozole per day (250 µg/kg total dose), from Days 1 to 3, Days 3 to 5, or Days 5 to 7 (Day 0 = pre-treatment ovulation,) corresponding to the periods before, during and after selection of the dominant follicle, respectively. Follicular dynamics were monitored ultrasonically and blood samples were collected for endocrine assays. Follicle diameter profiles and plasma LH, FSH, and estradiol concentrations were analyzed. Additionally, during the second trial, CL diameter profiles and plasma progesterone concentrations were measured. In both studies, the diameter profile of the dominant follicle was larger in heifers treated with letrozole than in control heifers (P<0.05) and the intervals to new wave emergence and onset of regression of the extant dominant follicle were longer (P<0.05) in heifers treated with letrozole than in controls, regardless of the dose (high, medium, or low; single vs multiple) and the stage of the follicle wave in which treatments were initiated. Furthermore, during the second experiment, the mean CL diameter was larger in letrozole-treated heifers, although there were no differences in plasma progesterone concentrations between treated and control animals. The effects on dominant follicle and CL diameter profiles appeared to be the result of the significantly increased plasma LH concentrations observed in letrozole-treated animals during both treatment approaches (single vs multiple dose). Incomplete and inconsistent inhibition of estradiol production and the lack of a surge on FSH observed in both experiments may be a result of insufficient circulating levels of letrozole during the treatment period. In summary, a single or multiple dose of letrozole did not induce regression of the extant dominant follicle, nor did it directly affect FSH release. Conversely, letrozole extended the lifespan of the dominant follicle, in association with increased endogenous levels of LH, thereby delaying the next FSH surge and subsequent follicular wave emergence. Results suggest that letrozole has potential as a non-steroidal method for controlling ovarian function in cattle, but further studies are warranted to clarify dosage and timing of treatment to predictably affect follicular wave dynamics in cattle.

Estrous synchronization (ES) protocols enhances profitability of beef cow-calf operations by improving percentage of cows pregnant early in the breeding season and increasing kg of calf weaned per cow exposed. Many factors, however, influence the fertility of cattle enrolled to ES protocols. The overall goal of this work was to determine the influences of estrus expression and timing of artificial insemination (AI), as well as temperament on fertility of Bos taurus beef females exposed to ES protocols. Multiparous cows (n = 1,676) were enrolled to the 7-d CO-Synch+ Controlled internal drug releasing device (CIDR) protocol and cows expressing estrus were inseminated. Cows not expressing estrus received a gonadotropin-releasing hormone injection and were either inseminated immediately or delayed by 8 hours. Pregnancy rates were greater for cows expressing estrus to the protocol. Delaying AI for 8 hours in cows that failed to express estrus did not improve pregnancy rates. The effects of temperament on fertility of beef heifers enrolled to the 7-d CO-Synch+CIDR protocol were investigated. Heifers (n = 297) had temperament assessed by chute score and exit velocity, and classified as adequate or excitable. Hair and blood were collected for cortisol evaluation. Pregnancy rates were greater for adequate temperament heifers. Circulating cortisol concentrations were greater for excitable heifers, and overall plasma and hair cortisol concentrations were reduced from the start of the protocol to the end. Heifers with adequate temperament have improved fertility and ES protocols acclimated heifers and reduced plasma and hair cortisol concentrations due to handling. / Master of Science / Infertility is a major issue that affects profitability of beef cow-calf producers. Estrous synchronization (ES) protocols are a tool that allow artificial insemination (AI) without estrus detection and increases the proportion of females pregnant at the start of the breeding season, providing a strategy to improve profitability. However, females enrolled in the ES protocol and that fail to express estrus have reduced pregnancy rates when compared to females expressing estrus. Furthermore, beef females with excitable temperament have reduced fertility when compared to females with adequate temperament. The effects of delaying insemination to 8 hours post injection of gonadotropin-releasing hormone for animals failing to express estrus during ES were determined in beef multiparous cows. Cows expressing estrus had greater pregnancy rates compared to cows not expressing estrus, and delayed insemination did not improve pregnancy rates. To determine the effects of temperament on fertility heifers were enrolled in an ES protocol and had temperament determined as adequate or excitable based on chute score and exit velocity. Hair and blood samples were collected for cortisol evaluation. Excitable heifers had reduced pregnancy rates and greater circulating cortisol concentrations, but hair cortisol did not differ between temperaments. Overall cortisol profiles indicate that heifers became acclimated to handling during ES protocol. Development of ES that maximizes estrus expression prior to AI and selection of cattle with adequated temperament can enhance profitability of cow-calf operations.

O objetivo do estudo realizado no Laboratório de Pesquisa em Suínos, da Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, Pirassununga – SP, foi verificar os efeitos combinados de gonadotrofinas exógenas, (eCG e LH) e flushing sobre a duração e dispersão da manifestação do primeiro e segundo estros, ciclicidade das fêmeas, número de ovulações, viabilidade embrionária e freqüência de cistos ovarianos. Foram utilizadas 72 marrãs pré-púberes da linhagem Pen Ar Lan NAIMA®, com idade média de 157,49±5,01 dias, e 96,65±7,70kgs de peso, distribuidas em quatro tratamentos, em arranjo fatorial, com e sem flushing , e com e sem hormônio. A ração utilizada continha 16% de PB e 3.286,73 kcal/kg ME. A partir do 7º dia do primeiro estro, induzido com hormônio, as fêmeas do tratamento com flushing receberam 50% de incremento da mesma ração. No 16º dia, após o primeiro estro, as marrãs no tratamento hormonal receberam aplicação de 600 UI de eCG (Novormon®) e 2,5 mg de LH (Lutropin®), 72 horas após. Todas as marrãs foram expostas ao macho duas vezes ao dia, a partir do 10º dia e inseminadas ao segundo estro com sêmem heterospérmico contendo 4 x 109 espermatozóides. Ao abate, realizado no 5º dia após a inseminação, os genitais foram colhidos para exame dos ovários e coleta dos embriões. Não se observou interação entre os fatores. Os efeitos analisados em separado, não evidenciaram diferença significativa no Número de ovulações (14,28±5,06 vs 13,47±5,57 com e sem Flushing e 14,60±5,78 vs 13,23±4,83 com e sem Hormônio, respectivamente, P>0,05), na freqüência de cistos ovarianos (22,86% vs 11,11%, com e sem Flushing e 15,15% vs 18,42%, com e sem Hormônio, respectivamente,. P>0,05), na Manifestação do 2º estro (85,71% vs 91,43% com e sem Flushing e 90,63% vs 86,84% com e sem Hormônio, respectivamente, P>0,05), no Peso Final (115,35±8,23 vs 111,56±8,30kg, com e sem Hormônio, respectivamente, P>0,05), na Espessura de toucinho (10,0±2,0 vs 10,2±1,8mm com e sem Hormônio, respectivamente, P>0,05), e na Duração dos estros (57,68±20,02 vs 59,68±14,76 horas, com e sem Hormônio e 57,75±14,99 vs 59,62±19,43 horas, com e sem Flushing, respectivamente, P>0,05). Constatou-se diferença significativa na Viabilidade embrionária (11,55±4,81 vs 8,50±5,32 embriões viáveis, com e sem Flushing e 8,39±5,66 vs 11,25±4,58 embriões viáveis, com e sem Hormônio, respectivamente P=0,02), indicando valor superior para o tratamento com Flushing e inferior no grupo com Hormônio. No Peso final (117,48±9,82 vs 109,28±7,57kg, com e sem Flushing, respectivamente, P=0,0001) e na Espessura de toucinho (10,7±2,2 vs 9,5±1,9kg, com e sem Flushing, respectivamente, P=0,03) o valor superior ficou para o grupo com Flushing. Concluiu-se no estudo a não interação dos efeitos, entre os fatores Hormônio e Flushing . O uso das gonadotrofinas (eCG e LH) reduziu a dispersão de manifestação do segundo estro, sendo efetiva a sua sincronização. O emprego do Flushing no primeiro ciclo estral em marrãs influenciou positivamente a viabilidade embrionária e na associação do eCG e LH mais Flushing não notou-se efeito interativo, identificando-se diminuição da viabilidade embrionária, pela ação hormonal. / The objective of this study, held at the Swine Research Laboratory of the School of Veterinary Medicine and Zootechnology of the Univ. of São Paulo in Pirassununga, São Paulo, was to verify the combined effects of exogenic gonadotropin (eCG and LH) and flushing on the duration and dispersion of the manifestation of initial and second estruses, cyclicity of females, number of ovulations, embryonic viability, and frequency of ovarian cysts. Used for the experiment were 72 pubertal gilts of Pen Ar Lan NAIMA® lineage, with an average age of 157.49±5.01 days, and weight of 96.65±7.70kg. They were distributed in four treatments in a factorial arrangement, with and without flushing, and with and without hormone treatment. The feed used contained 16% CP and 3,286.73 kcal/kg ME. Starting on the seven day of the first estrus, induced with homone, the females with flushing treament received a 50% increase in the amount of the same type feed that they had been receiving. On the sixteenth day of the first estrus the gilts that received hormone treatment were given 600 UI of eCG (Novormon®) and 2.5 mg of LH (Lutopin®), 72 hours later. All the gilts were exposed to boar twice at day, starting on the tenth day and inseminated during the second estrus with heterospermic semen containing 4 x 109 spermatozoon. At slaughter on the fifth day after insemination, the genitals were removed to examine the ovaries and collect the embryos. Interaction between the factors were not observed. The effects that were analyzed separately did not show significant differences in the number of ovulations (14.28±5.06 vs 13.47±5.57 with and without flushing, and 14.60±5.78 vs 13.23±4.83 with and without hormones, respectively, P>0.05), in the frequency of ovarian cysts (22.86% vs 11.11%, with and without flushing and 15.15% vs 18.42% with and without hormones, respectively, P>0.05), during the second estrus (85.71% vs 91.43% with and without flushing and 90.63% vs 86.84% with and without hormones respectively, P>0.05), at final weight (115.35 ± 8.23 vs 111.56 ± 8.30kg, with and without hormones, respectively, P>0.05), in the backfat (10.0±2.0 vs 10.2±1.8mm with and without hormones, respectively, P>0.05), and in the duration of the estruses (57.68±20.02 vs 59.68±14.76 hours, with and without hormones and 57.75±14.99 vs 59.62±19.43 hours, with and without flushing, respectively, P>0.05). A significant difference was found in embryonic viability (11.55±4.81 vs 8.50±5.32 viable embryos, with and without flushing and 8.39±5.66 vs 11.25±4.58 viable embryos with and without hormones, respectively P=0.02), which indicated higher numbers when treated with flushing and lower numbers when treated with hormones. At the final weight (117.48±9.82kg vs. 109.28±7.57kg with and without flushing respectively, P=0.0001) and in the backfat (10.7±12.2 vs 9.5±1.9kg, with and without flushing, respectively, P=0.03) flushing resulted in a higher number. It is concluded in this study that there is a lack of interactive effects between treaments with hormones and flushing. Utilization of gonadotropins (eCG e LH) reduced the dispersion of the second estrus within an effective synchronization. The utilization of flushing in the first estrous cycle in gilts gave positive results as regards to embryonic viability. The association of eCG and LH, plus flushing did not show an interactive effect, and a reduction was identified in embryonic viability based the action of hormones.

Estrous synchronization and artificial insemination (ESAI) are reproductive technologies that cattlemen can use to improve the reproductive performance of their herds. Controlling the gender ratio of the calf-crop can also improve the opportunity for increased revenue and profit. Producers are able to shift and/or control the gender ratio of their calf crop by incorporating sex-sorted semen into their AI programs. However, decreased conception rates to AI have been previously observed when sex-sorted semen was used in comparison to conventional semen of the same sires. The objective of the first study was to determine if conception rates will differ in females inseminated with conventional semen or SexedULTRA™ sex-sorted semen when estrus is synchronized using an industry-standard, 7-d CO-Synch + Controlled Internal Drug Release (CIDR) protocol for fixed-time artificial insemination (FTAI). The objective of the second study was to determine if conception rate to FTAI differs between SexedULTRA™ sex-sorted and conventional semen when yearling beef heifers are synchronized using a 14-d controlled internal drug release (CIDR) - PGF2α (PGF) protocol modified to optimize the control of ovulation and timing of insemination.