Objectives were to evaluate time of insemination relative to estrus and synchronization with melengestrol acetate (MGA) plus prostaglandin (PG) or progesterone insert (CIDR) plus PG on AI pregnancy rate in beef heifers (n = 662) during Fall or Spring. Fall heifers (n = 349) received MGA-PG (MGA for 14 d followed by PG on d 18) or CIDR-PG (CIDR for 7 d, PG administered 1 d before CIDR removal). Estrus was monitored by HeatWatch® (n = 200) or visually (n = 149). Spring heifers (n = 313) underwent CIDR-PG with detection of estrus by HeatWatch®. Heifers not in estrus by 96-100 h after PG were bred AI as non-responsive AI (NRAI). Across seasons, 548 heifers were bred following estrus (EAI). Heifers synchronized during the Fall with MGA received more (P < 0.05) mounts than Fall CIDR heifers (76.8 ± 6.7 and 47.6 ± 7.4, respectively), but duration of estrus was similar. Fall CIDR heifers had greater (P < 0.05) mounting activity and duration of estrus (47.9 ± 5.2 mounts and 15.5 ± 1.1 h) compared to Spring CIDR heifers (34.5 ± 3.1 mounts and 12.7 ± 0.6 h). Heifers grouped in 4 h blocks from 0 to 24 h had no difference (P > 0.05) in pregnancy rates (mean 62.5 %). Treatment had no effect (P > 0.05) on EAI pregnancy rates. Pregnancy rates across seasons for EAI, NRAI and overall was 61.0 %, 26.3 %, and 54.5%. In conclusion, a 24 h window may exist to successfully AI heifers. / Master of Science

For many cattle operations, profitability depends on the success of reproductive management programs. Opportunities for improving fertility exist within the numerous challenges related to reproductive management. Non-conventional, creative tools for reproductive management could help producers overcome these challenges. In an effort to produce information that could be used to improve reproductive performance of cattle, the following studies were undertaken. The objectives of these studies were threefold: to determine whether GnRH administered as an epidural injection causes ovulation in healthy cows and heifers, to evaluate whether the follicular environment (specifically, follicle fluid) surrounding the oocyte during the maturation phase affects the ability of the cumulus-oocyte complex to progress through early embryonic development, and to investigate the relative effects of estradiol and progesterone on oocyte maturation and early embryo development. Ability of GnRH to elicit an ovulatory response when administered as an epidural was evaluated in crossbred angus cows and heifers. The preliminary study evaluated this route of administration in crossbred angus cows. Animals were assigned randomly to either intramuscular or epidural administration, and ovaries were visualized via transrectal ultrasound every 6 h until ovulation of the dominant follicle. Results indicated that epidural administration of GnRH was able to trigger an ovulatory response, but timing of ovulation was not measured. The main experiment evaluated incidence of ovulation, time to ovulation, and ovulatory follicle size in crossbred angus heifers administered GnRH either epidurally or intramuscularly. Heifers were randomly assigned to treatment and ovaries were visualized every 4 h via transrectal ultrasound until ovulation of the dominant follicle. Results indicated that epidural administration of GnRH was able to elicit an ovulatory response in heifers, and the timing of ovulation and ovulatory follicle size was not different between administration route. Further investigation is needed to determine if characteristics of the ovulatory response (such as the luteinizing hormone surge) and circulating concentrations of GnRH are altered by epidural administration, which may impact fertility. GnRH administration is standard practice in many estrous synchronization programs. For fixed-time artificial insemination programs, the detection of estrus prior to insemination has been shown to improve conception and decrease early embryonic loss. The impact of behavioral estrus expression on the oocyte and early embryo were evaluated. Oocytes were matured in vitro in follicle fluid collected from synchronized cows who were classified as having expressed behavioral estrus or not expressing estrus. Embryo cleavage was not affected by estrus expression, but there was a tendency for improved blastocyst development in embryos matured in follicle fluid from animals who had expressed estrus. Cell number was not affected by estrus expression, but future research is needed as to the effect on oocyte acquisition of competence and early embryonic development. Despite the progress that has been made in culture conditions for in vitro produced embryos, developmental capacity following fertilization is limited at best, with only around one-third of oocytes placed into maturation resulting in viable embryos. During in vivo maturation, the oocyte undergoes final maturation within the follicle, surrounded by a changing microenvironment of estradiol and progesterone. Although the effects of steroids on oocyte development in vitro have been studied on an individual basis, a direct comparison between the ratio of estrogen and progesterone relative to follicle size has not been investigated Effects of steroid hormones estradiol and progesterone on oocyte maturation and early embryonic development were evaluated. Oocytes were matured in vitro in media supplemented with either estradiol, progesterone, or a combination of estradiol and progesterone. Oocytes were fertilized after maturation and cultured for 7 d until development to blastocyst stage. Addition of estradiol alone did not support oocyte maturation or early embryonic development in vitro, and a combination of estradiol and progesterone exhibited an inhibitory effect on oocyte maturation and early embryonic development. Addition of progesterone alone resulted in improved development when compared with estradiol alone or a combination of estradiol and progesterone. These results indicate that efficiency of reproductive management programs is controlled by multi-faceted factors and opportunities for improvement of reproductive outcomes exist in all of these factors. Although ovulation can be elicited via epidural administration, the impact of this ovulatory trigger on fertility requires further investigation. Display of estrus after synchronization for fixed-time artificial insemination improves conception and decreases early embryonic loss and has a may improve blastocyst development. This effect on early embryo development could be the focus of future research, further improving fertility and possibly the efficacy of in vitro embryo production. Steroid hormones play crucial roles in oocyte competency and the addition of progesterone during in vitro maturation improves development compared with estradiol alone or a combination of estradiol and progesterone. / Ph. D. / Reproductive success is critical for economic sustainability for many cattle operations. Creative tools for fertility management could help cattle producers overcome many challenges to fertility. In an effort to produce information that could be used to improve reproductive performance of cattle, the following studies were undertaken. The objective of these studies was to determine whether hormone administration as an epidural injection causes ovulation in healthy cattle (young and mature cattle assessed). Additionally, the second study evaluated whether the follicle (fluid-filled compartment surrounding the egg on the ovary) environment affects the female egg prior to ovulation, and the early embryo after fertilization. Finally, the third study looked at the impact of follicle fluid and specific hormones on embryo growth. An experiment was conducted in cows and heifers to determine if administering a hormone as an epidural injection, as opposed to conventional methods, could cause ovulation of the follicle. Animals received either an intramuscular or epidural hormone injection, and the ovaries of the animals were observed on an ultrasound until the follicle ruptured, releasing the egg. Epidural administration of the hormone was indeed able to trigger the rupture of the follicle. Hormone administration is standard practice in many cattle fertility programs. To maximize fertility, animals need to come into “heat” or estrus (period of sexual receptivity). Coming into heat is important for fertility in the female as it is indicative of impending ovulation and preparation of the egg for fertilization. In some reproductive management systems, reproductive cycles can be controlled in ways that deemphasize the need for behavioral estrus. Recent reports have suggested that animals in these systems that exhibit behavioral estrus are more fertile, as it makes it more likely for the female to conceive and stay pregnant compared to females who do not come into heat. The impact of heat on the female egg and early embryo of the cow has not been investigated. To evaluate the impact of heat on embryos, eggs were taken from the ovary of the cow and matured in a cell culture lab overnight in media containing fluid taken from the follicles of animals who came into heat, and animals that did not come into heat. The eggs were then fertilized, and embryos developed. There was only a tendency for improvement in embryo development for those matured in fluid from animals in heat compared with animals not in heat. When growing embryos in a culture lab, success rates are lower than embryos developing in the animal. When the egg is being prepared for release, it goes through important maturation steps to enable fertilization and eventual growth into a calf. Hormones in the follicle fluid facilitate maturation, and the conditions in the follicle are not easily replicated in the lab. The addition of these critical hormones to the lab conditions may help facilitate improved development in lab-produced embryos. Two hormones (estrogen and progesterone) were added to follicle fluid that was used in the lab culture environment to determine their effect on embryo growth. When progesterone was added, embryos grew well, matching the development rate of the control medium. When estrogen was added, embryos experienced poor development. Neither resulted in embryo development that exceeded the control medium. These results indicate that control of reproduction in cattle is complex, and multiple opportunities exist to improve fertility. Future research on how the oocyte and embryo react to their environment is needed and will facilitate further improvement of reproductive management systems in cattle. Improved reproductive management will enhance efficiency, sustainability and profitability of cattle production systems.

LD2668 .T4 1966 Z86 / Master of Science

Call number: LD2668 .T4 1978 O36 / Master of Science

Thesis (MSc)--Stellenbosch University, 2004. / Full text to be digitised and attached to bibliographic record. / ENGLISH ABSTRACT: Different synchronization and superovulation treatments were evaluated in the South African Boer goat (n = 367). Two progestagen implants, Synchro-Mate-B (SMB)/Crestar™ and Controlled Internal Drug Releases (CIDR), containing 3mg norgestomet and 0.33gm of natural progesterone, respectively, were used in the synchronization treatments. A luteolytic agent, Estrumate (Cloprostenol) 125)lg, was administered 12h before progestagen withdrawal. Synchronization treatment groups were: 1) 5MB x 1 (n = 123), one dose of 5MB for 13 to 17 days; 2) 5MB x 2 (n = 32), two doses of 5MB implanted for 10then 17 days; 3) CIDR x 1 (n = 187), one dose of CIDR; 4) CIDR x 2 (n = 25), two doses of CIDR, inserted for 9 to 17 days. On day 1 of the treatment, 0.5mg of estradiol cypionate (ECP) was administered to a group of randomly chosen goats (n = 112). Superovulation treatments consisted of Ovagen ™ or Embryo-STM. An additional single dose (300 UI) of Pregnant Mare Serum Gonadotropin (PMSG) was administered to a group of randomly chosen does. Superovulation treatment groups were: 1) OV alone (n = 147), Ovagen 9 mg every 12h, 8 times starting 72h prior to progestagen removal; 2) OV + PMSG (n = 164), same treatment as 1 plus 300 ru ofPMSG once 48h prior to progestagen removal; 3) E-S alone (n=16), Embryo-S 25 units twice a day, 8 times starting 72h before progestagen removal; 4) E-S + PMSG (n=40), same treatment as 3 plus 300 ru of PMSG once 48h prior to progestagen removal. Most does were naturally bred to bucks. Embryos were collected using the surgicallaparascopic procedure on day 6 and corpora lutea counted. Data were not normally distributed and therefore analyzed using a nonparametrie test (Wilcoxon, 1945 and Kruskal- Wallis, 1952) with outcome variable using the Mixed Procedure of SAS and the Tukey test. Differences were considered significant at p<0.05. Slightly more CL were on the left (52%) than on the right (48%) ovary. Superovulation treatment was significantly associated (p<O.OOl) while synchronization treatment was only marginally associated (p=0.06) with ovulation rate. Ovagen alone and Ovagen + PMSG were significantly more effective (p<0.05) than Embryo-S alone or Embryo-S + PMSG in influencing ovulation. Only synchronization treatment with 2 doses of CIDR was significantly more (p=0.04) effective in producing a high ovulation rate. Superovulation treatment was significantly (p=0.02) associated with the number of transferable embryos while synchronization treatment was not. Ovagen + PMSG was significantly (p=0.02) effective in producing more transferable embryos than Embryo-S + PMSG. Both superovulation and synchronization treatments were significantly (p<0.05) associated with producing unfertilized oocytes. Effectiveness of addition of ECP was shown in its association (p=0.05) with better quality embryos in univaraete analysis, though it did not have significant effect in the multivariate model. Though there was apparent advantage of CIDR over 5MB, no significant difference in ovulation rate or embryo quality was associated with synchronization treatments. Effectiveness of Ovagen over Embryo-S was demonstrated and addition ofPMSG improved embryo quality. / AFRIKAANSE OPSOMMING: Verskillende sinkronisasie en multi-ovulasie behandelings is ge-evalueer in die Suid-Afrikaans Boerbok (n= 367). Twee progestagene, Synchro-Mate-B (SMB)/Crestar™ en Controlled Internal Drug Releases (CIDR), bevattende 3mg norgestomet en 0.33gm natuurlike progesteroon, respektiewelik, is gebruik tydens die sinkronisasiebehandelings. 'n Luteolitiese middel, Estrumate (Cloprostenol) 125J.lg, is toegedien 12 h voor progestageen verwydering. Sinkronisasie behandelings groepe was: 1) 5MB x 1 (n = 123), een dosis 5MB vir 13 tot 17 dae; 2) 5MB x 2 (n = 32), twee dosisse 5MB implante vir 10 tot 17 dae; 3) CIDR x 1 (n = 187), een CIDR vir die hele periode; 4) CIDR x 2 (n = 25), twee CIDRs, vir 9 tot 17 dae. Op dag 1 van die behandeling is 0.5mg estradiol cypionate (ECP) aan 'n willekeurige groep bokooie toegedien (n = 112). Multi-ovulasie behandelings het bestaan uit Ovagen™ of Embryo-S™. 'n Bykomstige dosis (300 UI) Dragtige Merrie Serum Gonadotrofien (PMSG) is toegedien aan 'n willekeurige groep ooie. Multi-ovulasie behandelingsgroepe was: 1) OV alleen (n = 147), Ovagen 9 mg elke 12h, 8 keer beginende 72 h voor progestageen verwydering; 2) OV + PMSG (n = 164), selfde behandeling as in (1) plus 300 IV PMSG eenmalig 48h voor progestageen verwydering; 3) E-S alleen (n=16), Embryo-S 25 eenhede tweemaal per dag, ag inspuitings beginende 72h voor progestageen verwydering; 4) E-S + PMSG (n=40), selfde behandeling as in (3) plus 300 IV PMSG eenmalig 48h voor progestageen verwydering. Die meerderheid ooie is natuurlik deur ramme gedek. Embrio's is gekollekteer deur gebruik te maak van die chirurgieslaparoskopiese metode op dag 6 en die aantal corpora lutea getel en aangeteken. Aangesien die data nie 'n eweredige verspreiding gehad het nie, is dit geanaliseer deur gebruik te maak van 'n nie-parametriese toets (Wilcoxon, 1945 en Kruskal-Wallis, 1952) met variërende uitkomste deur die Gemengde Prosedure Toets van SAS en die Tukey toets. Verskille is as beduidend aanvaar met 'n P-waarde van <0.05. Onbeduidend meer CLs is op die linker (52%) as op die regter (48%) ovarium opgemerk. Multi-ovuasie behandelings was beduidend geassosieer (p<0.001) met ovulasietempo, terwyl sinkronisasie behandelings net marginaal geassosieer was (p=0.06) met ovulasietempo. Ovagen alleen en Ovagen + PMSG was beduidend meer effektief (p<0.05) as Embryo-S alleen of Embryo-S + PMSG om ovulasie te beïnvloed. Slegs die sinkronisasie behandeling met 2 dosisse CIDR was beduidend meer (p=0.04) effektief om 'n hoër ovulasietempo te veroorsaak. Multi-ovulasie behandeling was beduidend geassosieer met die aantal oordraagbare embrio's, terwyl sinkronisasie nie dieselfde tendens gewys het nie. Ovagen + PMSG het beduidend meer (p=0.02) oordraagbare embrio's opgelewer as Embryo-S + PMSG. Beide multi-ovulasie en sinkronisasie behandelings was beduidend geassosieer (p<0.05) met onbevrugte oosiete. Die rol van die byvoeging van ECP is getoon in die assosiasie daarvan (p=0.05) met beter kwaliteit embrio's in 'n eenvariante analiese, alhoewel dit nie 'n beduidende effek op die multi-variante model gehad het nie. Alhoewel dit blyk dat CIDR 'n beter reaksie as 5MB gee, kon geen beduidende verskil in die ovulasietempo of embriokwaliteit opgewys word nie. Die groter effektiwiteit van Ovagen oor Embryo-S is gedemonstreer, terwyl die byvoeging van PMSG embriokwaliteit verbeter het.

An estrus synchronization trial was conducted to determine the efficacy of adding an injection of gonadotropin releasing hormone (GnRH) at initiation of the controlled intravaginal drug releasing device (CIDR®) progesterone synchronization protocol in heifers. Nulliparous (n=121) beef heifers were randomly assigned to one of two treatment groups. All heifers received a CIDR® implant at the initiation of the breeding season. Half of the heifers (Select Synch) received an injection of GnRH. Heifers in the Select Synch treatment group had a lower numerical response (76.7% versus 88.3%) to treatment (detected in heat) and an overall lower artificial conception rate (46.0% versus 53.3%), but no statistical difference was detected. Days to conception and artificial insemination conception rates for both groups were similar for all heifers inseminated. Three hundred multiparous Hereford, crossbred and composite beef cows were assigned to one of two breeding groups (Early and Late) based on calving date and randomly assigned to receive an injection of GnRH at the time of CIDR® insertion (Select Synch). The addition of GnRH did not impact the percentage of cows detected in estrus or days to conception. Conception rates were not affected by the addition of GnRH (Select Synch), however cows in the early breeding group were more likely to become pregnant (58% versus 45%) by artificial insemination (P<0.02). An experiment evaluated the efficacy of the CIDR® protocol to synchronize estrus in Arizona Holstein dairy cows (n=696). Cows assigned to the CIDR® protocol (n=337) received a CIDR® insert at the end of the voluntary waiting period (55 days). CIDR®s were removed and an injection of prostaglandin was administered seven days after insertion. There was no difference due to CIDR® treatment in number of services per conception or first service conception rate. CIDR® treatment reduced days to first service, days open at first service, and days open (P<0.02). Warm season had a deleterious effect on number of services, days to first service, first service conception rate and days open (P<0.0001). In summary, estrus synchronization improved postpartum reproductive performance; however, thermal stress continues to be a major barrier to reproductive efficiency.

Call number: LD2668 .T4 1986 N484 / Master of Science / Animal Sciences and Industry

O sucesso no emprego da inseminação artificial em suínos depende de inúmeros fatores, sendo o momento ideal de sua realização, um dos que mais influencia, o qual compreende um intervalo entre 0 e 24 horas antes da ovulação. Estudou-se as relações entre o intervalo desmame-cio (IDC), a duração do cio (DC) e o momento da ovulação (MO) e a influência da raça, ordem de parto e estação do ano sobre estas características e suas relações. Um total de 236 fêmeas, de uma unidade de produção de suínos no oeste Santa Catarina, foram observadas para a obtenção dos dados de IDC e DC, as quais eram testadas para o diagnóstico de cio 4 vezes ao dia, na presença do macho. A ovulação foi diagnosticada em 77 fêmeas, pela ultra-sonografia, por via trans-cutânea, em 3 exames diários com 8 horas de intervalo. As amostras de sangue para análise de progesterona, foram coletadas de 74 fêmeas, com 24 horas de intervalo, em 4 ocasiões para a determinação dos níveis: basal, 24, 48 e 72 horas após o início do cio, respectivamente, e submetidas a técnica de radioimunoensaio. A raça Landrace mostrou um IDC mais longo (113,62 horas) em comparação à Large White (linhagem 1) (102,45 horas) (P<0,05), mas não houveram diferenças significativas destas em relação à Large White (linhagem 2). Fêmeas de 1º parto apresentaram um IDC mais longo (117,44 horas) que às de 2º parto (100,47 horas) e acima deste (104,78 horas) (P<0,05). Não houve influência da estação do ano sobre nenhuma das características. Houve interação entre estação do ano e ordem de parto sobre o MO, sendo que, nas fêmeas acima de 2º parto, o MO médio estimado foi de 51,76 horas na estação 1 e de 36,56 horas na estação 2 (P<0,05). Houve correlação negativa entre intervalo desmame-cio e duração do cio (r=-0,4657; P=0,0001) e entre intervalo desmame-cio e momento da ovulação (r=-0,3955; P=0,0004), no entanto, não houve correlação entre duração do cio e momento da ovulação (r=0,2201; P=0,0578). Não foi possível mostrar influências de raça, ordem de parto e estação de ano sobre as relações entre IDC, DC e MO através da análise de regressão com comparação de retas. Houve baixa correlação entre a ultra-sonografia e a análise de progesterona (MOP), para o diagnóstico da ovulação (r=0,3396;P=0.0209), sem correlação quando a ocorrência da ovulação foi considerada em intervalos de 24 horas a partir do início do cio (r=0,2637;P=0,0766). A porcentagem de fêmeas que, pela ultra-sonografia, ovularam entre 0 e 24, 24 e 48, 48 e 72 e acima de 72 horas após o início do cio foi de, respectivamente, 0%, 58,4%, 37,5% e 4,2% para o IDC de 3 dias, 3,2%, 67,7%, 29,2% e 0% para o IDC de 4 dias, 0%, 91,6%, 8,3% e 0% para o IDC de 5 dias e 10%, 90%, 0% e 0% para o IDC de 6 e 7 dias. Pela análise de progesterona, para os mesmos intervalos, respectivamente, a porcentagem fêmeas foi de 4,5%, 36,3%, 50% e 9,1% para o IDC de 3 dias, 3,6%, 32,2%, 60,7% e 3,6% para o IDC de 4 dias, 5,9%, 35,3%, 52,9% e 5,9% para o IDC de 5 dias e 14,3%, 57,1%, 28,6% e 0% para o IDC de 6 e 7 dias. Nestas condições, o I DC não se mostrou uma referência confiável para ser utilizado como um preditor do momento ideal da inseminação. No entanto, conhecimento das características IDC, DC e MO dentro de cada rebanho ajudam a apontar falhas e elaborar programas eficientes de IA. / The success of artificial insemination (AI) depends on several factors. The ideal moment to realize the AI is a limiting factor and it is defined as O to 24 hours before ovulation. Relationships between weaning-to-estrus interval (WEI), duration of estrus (DE) and moment of ovulation (MO) and the influence of breed, parity and season over these characteristics and the relationships with each other were studied. In a total of 236 sows, of a farm in the west of Santa Catarina, were observed to record the data of WEI and DE, which were tested by back pressure 4 times a day, in presence of a boar. The ovulation was diagnosed in 77 sows, by transcutaneous ultrasonography, 3 times a day at intervals of 8 hours. The blood samples to progesterone analyze were collected of 74 SOWS, at 24 hours intervals, at 4 occasions to determine basal, 24, 48, 72 hours levels after estrus onset, respectively, and submitted to radioimunoassay. The breed Landrace showed a WEI longer (113,62 hours) than Large White (Iine 1) (102,45 hours) (P<0,05), but there were no differences in relation to Large White (Iine 2). First parity sows presented a WEI longer (117,44 hours) than second parity sows (100,47 hours) and over second parity (104,78 hours) (P<O,05). There was no influence of season over ali the studied characteristics. There was interaction between season and parity over MO because females over second parity showed an average MO of 51,76 hours in season 1 and 36,56 hours in season 2 (P<0,05). There was negative correlation between WEI and DE (r=-O,4657; P=O,0001) and between WEI and MO (r=-O, 3955; P=O,0004), however, there was no correlation between DE and MO (r=0,2201; P=0,0578). It was not possible to show influence of breed, parity and season over the relationships between WEI, DE and MO by analyze of regression with line comparison. There was low correlation between ultrasonography and analyze of progesterone (MOP), to diagnose ovulation (r=O,3396;P=0.0209) and no correlation when the occurrence of ovulation was considered at intervals of 24 hours since onset of estrus (r=O,2637;P=O,0766). The percentage of females that ovulated (detected by ultrasonography), between O to 24, 24 to 48,48 to 72 and over 72 hours after the onset of estrus was, respectively, 0%, 58,4%, 37,5% and 4,2% to WEI of 3 days, 3,2%, 67,7%, 29,2% and 0% to WEI of 4 days, 0%, 91,6%, 8,3% e 0% to WEI of 5 days and 10%, 90%, 0% and 0% to WEI of 6 and 7 days. By progesterone levels, for the same intervals, respectively, the percentage was 4,5%, 36,3%, 50% and 9,1% to WEI of 3 days, 3,6%, 32,2%, 60,7% and 3,6% to WEI of 4 days, 5,9%, 35,3%, 52,9% and 5,9% to WEI of 5 days and 14,3%, 57,1%, 28,6% and 0% to IDe of 6 and 7 days. In these conditions, the WEI was not a good reference to be utilized as a predictor of ideal moment of insemination. However, the information about the characteristics WEI, DE and MO within each herd help to point the mistakes and to develop AI programs.

O sucesso no emprego da inseminação artificial em suínos depende de inúmeros fatores, sendo o momento ideal de sua realização, um dos que mais influencia, o qual compreende um intervalo entre 0 e 24 horas antes da ovulação. Estudou-se as relações entre o intervalo desmame-cio (IDC), a duração do cio (DC) e o momento da ovulação (MO) e a influência da raça, ordem de parto e estação do ano sobre estas características e suas relações. Um total de 236 fêmeas, de uma unidade de produção de suínos no oeste Santa Catarina, foram observadas para a obtenção dos dados de IDC e DC, as quais eram testadas para o diagnóstico de cio 4 vezes ao dia, na presença do macho. A ovulação foi diagnosticada em 77 fêmeas, pela ultra-sonografia, por via trans-cutânea, em 3 exames diários com 8 horas de intervalo. As amostras de sangue para análise de progesterona, foram coletadas de 74 fêmeas, com 24 horas de intervalo, em 4 ocasiões para a determinação dos níveis: basal, 24, 48 e 72 horas após o início do cio, respectivamente, e submetidas a técnica de radioimunoensaio. A raça Landrace mostrou um IDC mais longo (113,62 horas) em comparação à Large White (linhagem 1) (102,45 horas) (P<0,05), mas não houveram diferenças significativas destas em relação à Large White (linhagem 2). Fêmeas de 1º parto apresentaram um IDC mais longo (117,44 horas) que às de 2º parto (100,47 horas) e acima deste (104,78 horas) (P<0,05). Não houve influência da estação do ano sobre nenhuma das características. Houve interação entre estação do ano e ordem de parto sobre o MO, sendo que, nas fêmeas acima de 2º parto, o MO médio estimado foi de 51,76 horas na estação 1 e de 36,56 horas na estação 2 (P<0,05). Houve correlação negativa entre intervalo desmame-cio e duração do cio (r=-0,4657; P=0,0001) e entre intervalo desmame-cio e momento da ovulação (r=-0,3955; P=0,0004), no entanto, não houve correlação entre duração do cio e momento da ovulação (r=0,2201; P=0,0578). Não foi possível mostrar influências de raça, ordem de parto e estação de ano sobre as relações entre IDC, DC e MO através da análise de regressão com comparação de retas. Houve baixa correlação entre a ultra-sonografia e a análise de progesterona (MOP), para o diagnóstico da ovulação (r=0,3396;P=0.0209), sem correlação quando a ocorrência da ovulação foi considerada em intervalos de 24 horas a partir do início do cio (r=0,2637;P=0,0766). A porcentagem de fêmeas que, pela ultra-sonografia, ovularam entre 0 e 24, 24 e 48, 48 e 72 e acima de 72 horas após o início do cio foi de, respectivamente, 0%, 58,4%, 37,5% e 4,2% para o IDC de 3 dias, 3,2%, 67,7%, 29,2% e 0% para o IDC de 4 dias, 0%, 91,6%, 8,3% e 0% para o IDC de 5 dias e 10%, 90%, 0% e 0% para o IDC de 6 e 7 dias. Pela análise de progesterona, para os mesmos intervalos, respectivamente, a porcentagem fêmeas foi de 4,5%, 36,3%, 50% e 9,1% para o IDC de 3 dias, 3,6%, 32,2%, 60,7% e 3,6% para o IDC de 4 dias, 5,9%, 35,3%, 52,9% e 5,9% para o IDC de 5 dias e 14,3%, 57,1%, 28,6% e 0% para o IDC de 6 e 7 dias. Nestas condições, o I DC não se mostrou uma referência confiável para ser utilizado como um preditor do momento ideal da inseminação. No entanto, conhecimento das características IDC, DC e MO dentro de cada rebanho ajudam a apontar falhas e elaborar programas eficientes de IA. / The success of artificial insemination (AI) depends on several factors. The ideal moment to realize the AI is a limiting factor and it is defined as O to 24 hours before ovulation. Relationships between weaning-to-estrus interval (WEI), duration of estrus (DE) and moment of ovulation (MO) and the influence of breed, parity and season over these characteristics and the relationships with each other were studied. In a total of 236 sows, of a farm in the west of Santa Catarina, were observed to record the data of WEI and DE, which were tested by back pressure 4 times a day, in presence of a boar. The ovulation was diagnosed in 77 sows, by transcutaneous ultrasonography, 3 times a day at intervals of 8 hours. The blood samples to progesterone analyze were collected of 74 SOWS, at 24 hours intervals, at 4 occasions to determine basal, 24, 48, 72 hours levels after estrus onset, respectively, and submitted to radioimunoassay. The breed Landrace showed a WEI longer (113,62 hours) than Large White (Iine 1) (102,45 hours) (P<0,05), but there were no differences in relation to Large White (Iine 2). First parity sows presented a WEI longer (117,44 hours) than second parity sows (100,47 hours) and over second parity (104,78 hours) (P<O,05). There was no influence of season over ali the studied characteristics. There was interaction between season and parity over MO because females over second parity showed an average MO of 51,76 hours in season 1 and 36,56 hours in season 2 (P<0,05). There was negative correlation between WEI and DE (r=-O,4657; P=O,0001) and between WEI and MO (r=-O, 3955; P=O,0004), however, there was no correlation between DE and MO (r=0,2201; P=0,0578). It was not possible to show influence of breed, parity and season over the relationships between WEI, DE and MO by analyze of regression with line comparison. There was low correlation between ultrasonography and analyze of progesterone (MOP), to diagnose ovulation (r=O,3396;P=0.0209) and no correlation when the occurrence of ovulation was considered at intervals of 24 hours since onset of estrus (r=O,2637;P=O,0766). The percentage of females that ovulated (detected by ultrasonography), between O to 24, 24 to 48,48 to 72 and over 72 hours after the onset of estrus was, respectively, 0%, 58,4%, 37,5% and 4,2% to WEI of 3 days, 3,2%, 67,7%, 29,2% and 0% to WEI of 4 days, 0%, 91,6%, 8,3% e 0% to WEI of 5 days and 10%, 90%, 0% and 0% to WEI of 6 and 7 days. By progesterone levels, for the same intervals, respectively, the percentage was 4,5%, 36,3%, 50% and 9,1% to WEI of 3 days, 3,6%, 32,2%, 60,7% and 3,6% to WEI of 4 days, 5,9%, 35,3%, 52,9% and 5,9% to WEI of 5 days and 14,3%, 57,1%, 28,6% and 0% to IDe of 6 and 7 days. In these conditions, the WEI was not a good reference to be utilized as a predictor of ideal moment of insemination. However, the information about the characteristics WEI, DE and MO within each herd help to point the mistakes and to develop AI programs.

<p>A series of experiments were designed to study alternative estrus synchronization and resynchronization protocols to facilitate the use of artificial insemination in cattle. </p><p>Studies were conducted to study the effects of estradiol cypionate (ECP) on follicular dynamics, time of ovulation, and pregnancy rate to timed-AI (TAI) in CIDR-based protocols. Although administration of 1 mg ECP did not result in synchronous follicular wave emergence, a dose of 0.5 mg ECP synchronized LH release and ovulation. Administration of ECP 24 h after CIDR removal resulted in acceptable pregnancy rate. However, treatment with ECP at CIDR removal resulted in acceptable pregnancy rate only if follicular wave emergence was synchronized with estradiol-17â (E-17â). </p><p>The efficacy of two estradiol preparations (5 mg of E-17â or estadiol valerate; EV) and reduced doses of EV on CL and ovarian follicular dynamics and superovulatory response were examined. When doses of 5 mg were compared, EV treatment resulted in a more variable interval to follicular wave emergence and a lower superovulatory response than E-17â. However, EV at a dose of 1 or 2 mg was efficacious in synchronizing follicle wave emergence in CIDR-treated cattle.</p><p>Pregnancy rates were compared following TAI in cattle given a new or previously used CIDR and injections of estradiol, with or without progesterone, to synchronize follicular wave emergence. Pregnancy rate following TAI did not differ between cattle treated with a new or once-used CIDR, but pregnancy rate was lower in cattle treated with one or two twice-used CIDR. The addition of an injection of progesterone to the estradiol treatment at CIDR insertion did not enhance pregnancy rate. </p><p>The efficacy of progestins (used CIDR and MGA), and E-17â, ECP, GnRH, or progesterone treatment for resynchronization of estrus in cattle not pregnant following TAI were investigated. Progestin treatment resulted in the majority of nonpregnant heifers detected in estrus over a 4-d interval. Conception rates were higher in heifers resynchronized with a once-used CIDR than with MGA. GnRH at CIDR insertion synchronized follicular wave emergence in cows, but did not increase conception rate in heifers. E-17â at CIDR insertion (1.5 mg) and removal (0.5 mg) resulted in decreased pregnancy rate following TAI. In summary, protocols described in this thesis resulted in acceptable pregnancy rates following TAI and resynchronization of previously inseminated heifers with progestins resulted in variable estrus and pregnancy rates.</p>