Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the CO‐Synch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicus‐influenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day ‐7. The CO‐Synch + CIDR protocol included a CIDR insert and GnRH (GnRH‐1; day 0), removal of CIDR and PGF2α on day 7, and GnRH (GnRH‐2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS ≥ 5 tended to differ (P=0.085) between Presynch (38%) and CO‐Synch + CIDR (54%). In Exp. 2, ovulatory response to GnRH‐1 was greater (P<0.01) in the Presynchronization (58%) than in the CO‐Synch + CIDR (27.1%) group. Emergence of a follicular wave after GnRH‐1 and ovulation rate after GnRH‐2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRH‐1 ovulated (82%) after GnRH‐2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4±0.8) on day 0 and declined (P<0.01) to 95.2±0.8 and 82±0.8, respectively, on days 7 and 10. We observed a low negative but significant relationship (r=0.38; P<0.001) between VER and follicular size on day 0, 7, and 10. VER difference (day 10 minus day 7) did not differ between females with small and large follicles at TAI. Mean concentrations of P4 during the 7‐day insertion period were greater (P<0.03) for new (3.7 ng/ml) and re‐used autoclaved (3.4 ng/ml) than for re‐used disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRH‐1, but did not improve pregnancy rates compared to CO‐Synch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when re‐using CIDR inserts because it creates greater concentrations of P4 during the first 48 h.

Objectives were to determine: 1) whether estradiol benzoate (EB) provides a superior alternative to GnRH for synchronizing emergence, growth and maturation of a new follicular wave for fixed timed AI (TAI) in Bos indicus-influenced cattle using CIDR-based protocols, 2) the effect of 48 h calf removal at CIDR removal on the rate of maturational synchrony of the dominant follicle and 3) the effect of varying the magnitude of peak plasma progesterone (P4) concentrations following CIDR insertion on the suppression of FSH and LH secretion in a CIDR-based protocol using EB. In experiment 1, sixty-four Braford (F-1) females were stratified by BCS, parity and days postpartum and assigned randomly to one of four groups in a 2 x 2 factorial arrangement of treatments: 1) Select-Synch + CIDR, 2) Select-Synch + CIDR with 48 h calf removal, 3) E-Synch + CIDR or 4) E-Synch + CIDR with 48 h calf removal. A greater number of cattle in the EB treated group exhibited NFWE compared to the GnRH group, 29 vs 17 cows for EB and GnRH respectively, (P<0.0006). Intervals to NFWE were also greater in EB treated cattle than in GnRH treated cattle, 4.2 vs 2.7 d for EB and GnRH treated cattle respectively, (P<0.0001). Proportions of GnRH- and EB-treated cows ovulating after CIDR removal did not differ. Post-CIDR suckling status did not affect ovulation frequency or interval to ovulation. In experiment 2, eight pubertal (F-1) heifers were used in a Latin Square design with four treatment levels of P4: 1) EB only, 2) EB and new CIDR, 3) EB and new autoclaved CIDR, 4) EB, new autoclaved CIDR and P4 injection at CIDR insertion. Treatments 2 through 4 increased (P < 0.01) mean plasma P4 concentrations compared to treatment 1, with treatment 4 creating the greatest increase in P4 with the longest duration. Suppression of plasma FSH was greatest in group 4 (P<0.08), with mean 60 h concentrations less than in all other groups. Mean concentrations of LH were lesser in group 4 than groups 1 and 2. Frequencies of occurrence of NFWE and ovulation and intervals to NFWE did not differ among treatments. Results indicate that the use of EB and CIDR to synchronize Brahman x Hereford females may provide better synchronization for TAI compared to GnRH and CIDR based protocols.

Objectives were to determine: 1) whether estradiol benzoate (EB) provides a superior alternative to GnRH for synchronizing emergence, growth and maturation of a new follicular wave for fixed timed AI (TAI) in Bos indicus-influenced cattle using CIDR-based protocols, 2) the effect of 48 h calf removal at CIDR removal on the rate of maturational synchrony of the dominant follicle and 3) the effect of varying the magnitude of peak plasma progesterone (P4) concentrations following CIDR insertion on the suppression of FSH and LH secretion in a CIDR-based protocol using EB. In experiment 1, sixty-four Braford (F-1) females were stratified by BCS, parity and days postpartum and assigned randomly to one of four groups in a 2 x 2 factorial arrangement of treatments: 1) Select-Synch + CIDR, 2) Select-Synch + CIDR with 48 h calf removal, 3) E-Synch + CIDR or 4) E-Synch + CIDR with 48 h calf removal. A greater number of cattle in the EB treated group exhibited NFWE compared to the GnRH group, 29 vs 17 cows for EB and GnRH respectively, (P<0.0006). Intervals to NFWE were also greater in EB treated cattle than in GnRH treated cattle, 4.2 vs 2.7 d for EB and GnRH treated cattle respectively, (P<0.0001). Proportions of GnRH- and EB-treated cows ovulating after CIDR removal did not differ. Post-CIDR suckling status did not affect ovulation frequency or interval to ovulation. In experiment 2, eight pubertal (F-1) heifers were used in a Latin Square design with four treatment levels of P4: 1) EB only, 2) EB and new CIDR, 3) EB and new autoclaved CIDR, 4) EB, new autoclaved CIDR and P4 injection at CIDR insertion. Treatments 2 through 4 increased (P < 0.01) mean plasma P4 concentrations compared to treatment 1, with treatment 4 creating the greatest increase in P4 with the longest duration. Suppression of plasma FSH was greatest in group 4 (P<0.08), with mean 60 h concentrations less than in all other groups. Mean concentrations of LH were lesser in group 4 than groups 1 and 2. Frequencies of occurrence of NFWE and ovulation and intervals to NFWE did not differ among treatments. Results indicate that the use of EB and CIDR to synchronize Brahman x Hereford females may provide better synchronization for TAI compared to GnRH and CIDR based protocols.

Data were analyzed on 2 to 6 yr old cows to evaluate sire and family effects. Cows were produced in the McGregor Genomics Project from 13 embryo transfer (ET) full sib families (n = 188, F2 Nellore-Angus (NA)) and 4 half sib natural service (NS) families (n = 114, out of 1/2 Brahman 1/2 British dams) from the same 4 F1 NA sires. The ET and NS cows were analyzed separately and together as paternal half sibs (PHS). Daughters of bull 437J had the highest calving rate and weaning rate; daughters of 551G were the lowest in ET, and daughters of 297J were the lowest in NS. Calves out of daughters of 551G were the heaviest at birth; those from of daughters of 437J were the lightest in NS and PHS. Calves out of daughters of 297J were the heaviest at weaning in ET and PHS, and those from daughters of 432H were the lightest. Calves from daughters of 297J and 437J gained the most weight and those from daughters of 432H gained the least. Daughters of 297J and 551G had longer and larger diameter teats and lower udder support scores (more pendulous) than daughters of 432H and 437J. Daughters of 437J had the highest body condition score (BCS); daughters of 551G were the lowest in ET and NS. Calves from daughters of 297J had the highest BCS at weaning. Those out of daughters of 551G had the lightest WWT, those out of daughters of 437J were the heaviest in NS and PHS, and those out of daughters of 432H were the heaviest in ET. Daughters of 437J and 551G scored the highest for disposition (least docile) in ET and PHS, and daughters of 432H were lowest. The regression of WWT on weaning age was 0.82 plus/minus 0.07 in ET, 0.71 plus/minus 0.08 in NS, and 0.78 plus/minus 0.05 kg/d in PHS. There appears to be sufficient variation within and between these full sib and half sib families for use in QTL analysis for major genes affecting cow productivity in NA crosses.

Angus - Bos indicus (Brahman or Nellore) reciprocal backcross embryo transfer calves belonging to 28 full-sib families were evaluated for differences in birth weight (BW), gestation length (GL), weaning weight (WW), carcass weight (HCW), longissimus muscle area (REA), fat thickness (adjusted (ADJFAT) and actual(ACTFAT)), intramuscular fat (MARB), and Warner-Bratzler shear force tenderness (WBSF). Family types with a greater proportion of Bos indicus in the sire in relation to the amount in the dam (F1 x A and B x F1) averaged longer GL and heavier BW than their respective reciprocal crosses (A x F1 and F1 x B). Calves had longer GL when the F1 parent was BA as opposed to AB. Small differences (statistically insignificant) were detected for BW, but no consistent difference was found between offspring of AB and BA parental types, with the exception of male F1-sired calves. F1 x A and B x F1 crosses also showed a large BW difference between males and females (about 5.0 kg), while A x F1 and F1 x B crosses showed no BW difference between males and females. Further examination within each sex showed a difference between male reciprocals that was two times that of females. Calves with a higher percentage of Bos indicus in the sire compared to the proportion in the dam showed the same trend, as they were still heavier at weaning, and produced heavier carcasses than the reciprocal crosses, though these differences were not significant. As a whole, A backcross calves had more ACTFAT, more ADJFAT, larger REA, more MARB, and lower WBSF than B backcross calves, though no significant differences were detected between reciprocal crosses for any of these traits. These results suggest that for weight related traits, especially BW, both the breed constitution of the calf and the cross that produces the calf play an important role in its ultimate performance for Bos indicus crossbred calves. For carcass and meat related traits, it appears that the breed make-up of the calf itself is more significant in influencing performance than the cross used to produce the calf.

Reproductive and weight traits were analyzed for Angus (A), Brahman (B), Hereford (H), and Nellore (N) straightbred cows; F1 NA cows; 3/8N 5/8A cows and quarter blood composite cows (BANH) of the four straightbreds in Central Texas. Heterosis was estimated for calf crop born (CCB), calf crop weaned (CCW), and calf survival (CS) by linear contrasts within cow breed groups. F1 NA cows expressed heterosis (P < 0.0001) for CCB (0.22) and CCW (0.20). Except for the 3/8N 5/8Ac cows, which resulted from the mating of NA bulls to 3/4A 1/4N cows, all of the crossbred cow breed types expressed significant heterosis (P < 0.05) when compared to the weighted average of the parental purebreds for CCB. BANHc cows that were the result of mating NA bulls to HB cows expressed heterosis for CCB (0.35) (P < 0.001) and CCW (0.29) (P < 0.05). The 3/8N 5/8Aa females produced by mating 3/4N 1/4A bulls to NA cows expressed heterosis (P < 0.0001) for CCW (0.20). Heterosis for calf survival was near zero for all breed types, but only two breed types of 3/8N 5/8A cows were significantly greater than the weighted average of the parental purebreds. Heterosis for birth weight (BWT) and weaning weight (WWT) was also analyzed by linear contrasts within cow breed groups. The BANHb and BANHc cows produced from mating NA bulls to BH and HB F1 cows, respectively, expressed heterosis for BWT (2.89 + 0.79 (P < 0.001) and 3.38 + 1.51 (P < 0.05)). All cow breed types expressed significant heterosis (P < 0.05) for WWT. The BANH2 cows resulting from the mating of NA bulls to F2 HB or BH cows expressed heterosis (P < 0.0001) for WWT (52.01 kg + 9.88).

Objectives were to: 1) Evaluate the effectiveness of presynchronization with GnRH before the CO‐Synch + CIDR protocol with timed AI (TAI) at 66 h in Bos indicus‐influenced cattle; 2) Characterize ovarian events associated with the presynchronization; 3) Evaluate the efficacy of measuring vaginal electrical resistance (VER) to assess follicular maturity at TAI; and 4) Compare serum concentrations of progesterone (P4) in ovariectomized cows bearing new or previously used CIDR devices with or without autoclaving. In Exp. 1 and 2, cattle received either GnRH or saline on day ‐7. The CO‐Synch + CIDR protocol included a CIDR insert and GnRH (GnRH‐1; day 0), removal of CIDR and PGF2α on day 7, and GnRH (GnRH‐2) and TAI 66 h after CIDR removal. In Exp. 1, pregnancy rate of females with BCS ≥ 5 tended to differ (P=0.085) between Presynch (38%) and CO‐Synch + CIDR (54%). In Exp. 2, ovulatory response to GnRH‐1 was greater (P<0.01) in the Presynchronization (58%) than in the CO‐Synch + CIDR (27.1%) group. Emergence of a follicular wave after GnRH‐1 and ovulation rate after GnRH‐2 did not differ between groups. More (P<0.01) females that developed a follicular wave after GnRH‐1 ovulated (82%) after GnRH‐2, compared to those that did not (29%). Mean VER (ohms) was greatest (101.4±0.8) on day 0 and declined (P<0.01) to 95.2±0.8 and 82±0.8, respectively, on days 7 and 10. We observed a low negative but significant relationship (r=0.38; P<0.001) between VER and follicular size on day 0, 7, and 10. VER difference (day 10 minus day 7) did not differ between females with small and large follicles at TAI. Mean concentrations of P4 during the 7‐day insertion period were greater (P<0.03) for new (3.7 ng/ml) and re‐used autoclaved (3.4 ng/ml) than for re‐used disinfected CIDRs (2.8 ng/ml). In summary, Presynch improved ovulation rate after GnRH‐1, but did not improve pregnancy rates compared to CO‐Synch + CIDR. Follicular maturity estimation was not feasible using VER as applied in this study. Autoclaving may be the best option when re‐using CIDR inserts because it creates greater concentrations of P4 during the first 48 h.

Sire and family effects were evaluated for calf growth, udder and teat conformation, and reproduction traits in 2- to 4- yr-old cows from the McGregor Genomics Project. Cows were produced by embryo transfer (ET) and natural service (NS) from the same 4 F1 Nellore-Angus sires, and were analyzed separately. Sire of cow was significant for calf birth weight (P = 0.014) among ET cows, but not NS cows. Among NS families, calves from cows out of Brahman-Hereford dams were 2.0 kg heavier (P = 0.064) at birth than calves from cows out of Brahman-Angus dams. Sire of cow accounted for variation in weaning weight (P = 0.006) and preweaning ADG (P = 0.005) of calves from ET dams, but not NS dams. Family nested within sire also accounted for variation (P = 0.061) in weaning weights of calves from ET dams. Sire of cow was significant for average teat length in ET (P < 0.001) and NS (P = 0.013) cows. Sire of cow was significant for average teat diameter (P = 0.022) among NS cows. Sire of cow also affected udder support score (P = 0.002), cow disposition at calf birth (P = 0.002), and cow weight at weaning (P = 0.045) in ET cows. Family and cow age also accounted for variation in cow disposition at calf birth (P = 0.015, P = 0.041, respectively) and cow weight at weaning (P = 0.001, P < .001, respectively) among ET cows. Calf year of birth also affected (P < .001) cow weight at weaning among ET cows. For NS dams, calf year of birth (P = 0.012), cow age (P < .001), and parity nested within cow age (P = 0.005) affected cow weight at weaning. Although reproduction data were not formally analyzed, there appear to be substantial differences for calving rate and average calving date among these cow families. Data from this project will be used for identification of genetic markers for these cow productivity traits.

O projeto teve como objetivo avaliar os efeitos da inclusão do ionóforo narasina no suplemento mineral e proteinado sobre o consumo de suplemento pelos animais e sobre o desempenho de bovinos de corte durante a fase de recria mantidos em pastagem. Foram utilizados 150 machos nelore inteiros em um delineamento experimental de blocos completos, sendo a unidade experimental o lote de 5 animais. O experimento teve duração de 140 dias, composto por 5 perídos de 28 dias cada. Os tratamentos utilizados foram: CON Mistura mineral Controle (sem narasina), 1800 CON com adição de 1800 mg de narasina/kg da mistura mineral, 2750 - CON com adição de 2750 mg de narasina/kg da mistura mineral, PROT Suplemento Proteinado com 22% de proteína bruta (PB; sem narasina) e PROT 360 PROT com 360 mg de narasina/kg do suplemento. Os tratamentos foram confrontados através de contrastes ortogonais. A inclusão de narasina na mistura mineral aumentou o ganho médio diário (GMD) quando comparado ao CON no primeiro período (P = 0,01; 28d), entretanto, não houve efeito nos demais períodos. A inclusão de narasina diminuiu o consumo de suplemento nos três períodos iniciais (P &lt; 0,01 para ambos) quando comparado ao CON. Os tratamentos 1800 e 2750 foram semelhantes para a ingestão de suplemento (P = 0,89) e GMD (P = 0,70) em todo o experimento. Os animais dos tratamentos PROT e PROT 360 consumiram mais suplemento em relação aos animais dos tratamentos com mistura mineral (P &lt; 0,01 para todos os períodos) e proporcionaram animais mais pesados (P &lt; 0,01). A inclusão de narasina no suplemento proteinado otimizou seu uso nos dois primeiros períodos, pois obteve o mesmo GMD (P = 0,75 e P = 0,48, respectivamente), porém com menor ingestão de suplemento (P = 0,03 e P &lt; 0,01, respectivamente). Em conclusão, a narasina afeta o consumo de suplementos e desempenho em situações específicas, porém, de maneira geral a narasina não foi eficaz em melhorar a performance de bovinos de corte em fase de recria a pasto. / The present trial was carried out to evaluate the effect of narasin inclusion in mineral and protein supplements in the supplement intake and performance of grazing beef cattle. A hundred and fifty Nellore bull calves with 17.03 &#177; 0.06 months of age, initial body weight (BW) of 219.65 &#177; 1.62 kg, were assigned to the following treatments: mineral supplement (CON); mineral supplement + 1800 (1800) or 2750 (2750) mg narasin/kg of supplement; Protein mineral supplement (PROT) or PROT + 360 mg of narasin/kg of supplement (PROT 360). The bull calves were kept in a rotational stocking system with Brachiaria brizantha cv Marandu, during 5 periods of 28 days each. Adding narasin in the mineral supplement increased (P = 0.01) average daily gain (ADG) on the 1st period and decreased (P &lt; 0.01) supplement intake on the 1st, 2nd and 3rd periods compared to CON. Bull calves in the 1800 and 2750 treatments had similar supplement intakes (P = 0.89) and ADG (P = 0.70) at the end of the experiment. In addition, the animals of the PROT and PROT 360 treatments consumed more supplement than the animals of the mineral mix treatments (P &lt; 0.01 for all periods) and provided heavier animals (P &lt; 0.01). Narasin decreased the protein supplement intake and did not affect ADG on the 1st and 2nd periods. The narasin affects the intake of supplements and performance in specific situations, however in overall, narasin addition in mineral and protein supplements did not affect the performance of grazing bull calves.

Esse estudo está apresentado em Capítulo 1 (Protocolo de Superovulação com IATF em Bos taurus) e Capítulo 2 [Protocolos de superovulação com IATF em Bos indicus, com 3 experimentos; 1- Momento da administração de LH em vacas Nelore (Bos indicus) superovuladas e inseminadas em tempo fixo; 2- Efeito da administração de progesterona injetável no início do protocolo de sincronização para superovulação com IATF em vacas Nelore; 3- Efeito do número de inseminações em vacas Nelore superovuladas e inseminadas em tempo fixo]. No Capítulo 1 objetivou-se avaliar o momento da retirada do dispositivo de P4 (DIB®) e da administração de LH em vacas Holandesas. Dezesseis vacas receberam DIB (D-1) e 2mg de BE (D0). Superovulou-se com 200mg de FSHp em 8 doses decrescentes a partir do D4. No D6, administrou-se PGF e estabeleceram-se quatro grupos: P24LH48 (retirada do DIB 24h e LH 48h pós PGF); P24LH60 (retirada 24h e LH 60h); P36LH48 (retirada 36h e LH 48h) e P36LH60 (retirada 36h e LH 60h; fatorial 2x2; cross-over). Realizou-se a IATF 12 e 24h pós LH. Os efeitos principais para P24vsP36 e LH48vsLH60 foram: taxa de ovulação (TO; 49,9 &plusmn; 5,7 vs 60,9&plusmn; 4,8% e 53,1&plusmn;5,3 vs 57,5&plusmn;5,4%; P>0,05), estruturas totais (ETot; 4,4&plusmn;0,9 vs 5,0&plusmn;0,9 e 3,8&plusmn;0,7 vs 5,7&plusmn;1,0; P>0,05), embriões transferíveis (ET; 3,0&plusmn;0,7 vs 4,1&plusmn;0,9 e 2,3&plusmn;0,5a vs 4,9&plusmn;0,9b; P<0,05) e embriões congeláveis (EC; 2,9&plusmn;0,7 vs 3,8&plusmn;0,8 e 2,1&plusmn;0,5a vs 4,7&plusmn;0,9b; P<0,05). O LH 60h pós PGF aumentou o número de ET e EC em Holandesas. No Capítulo 2, estudaram-se diferentes protocolos de superovulação com IATF em Nelore. No Experimento 1, vinte vacas foram superovuladas (P24) e tratadas com LH 48h (G-LH48) ou 60h (G-LH60) pós PGF (cross-over). Não houve diferença (P>0,05) para: número de folículos >8mm no LH (FolLH; 12,5±1,5 vs 9,4±1,0) e TO (71,0±4,2 vs 64,6±4,0%). No entanto, verificou-se diferença (P<0,05) para: intervalo primeira/última ovulação (IntOV; 15,0±2,1a vs 21,0±1,7bh), ETot (7,5±1,0a vs 5,1±0,5b), ET (6,2±1,0a vs 3,1±0,5b) e EC (5,9±0,9a vs 2,5±0,5b). O LH 48h pós PGF apresentou maior eficiência em Nelore. No Experimento 2, dez vacas receberam o protocolo P36LH48 e foram divididas em dois grupos no D0: Grupo BE (2mg) + P4 (50mg; G-BE+P4) ou Grupo BE (2mg; G-BE; cross-over). Os resultados para o G-BE+P4 e G-BE foram: emergência da onda folicular (EM; 3,6&plusmn;0,2 e 4,0&plusmn;0,1 d; P>0,05), variação da EM (2,5 a 4,5 vs 3,5 a 4,5d; P=0,06), FolLH (16,2&plusmn;1,4 vs 18,5&plusmn;1,1; P>0,05), IntOV (32,4&plusmn;1,8 vs 33,6&plusmn;1,6h; P>0,05), ETot (7,7&plusmn;0,8 vs 9,2&plusmn;1,2; P>0,05), ET (6,2±0.6 vs 7,2±1,1; P>0,05), EC (5,1&plusmn;0,7 vs 6,3&plusmn;1,0; P>0,05) e ED (0,6&plusmn;0,2 vs 0,8&plusmn;0,2; P>0,05). Não houve efeito da P4 i.m no D0. No Experimento 3, dez vacas foram divididas em: G-1IATF (16h pós LH) e G-2IATF (12 e 24h pós LH; cross-over). Os efeitos dos tratamentos G-1IATF e G-2IATF foram: FolLH (16,2&plusmn;1,4 vs 14,8&plusmn;1,2; P>0,05), ETot (8,2±0,9 vs 7,2±0,8; P>0,05), ET (4,3±0,7 vs 4,2±0,6; P>0,05), EC (2,9±0,6 vs 2,8±0,4; P>0,05) e estruturas não fertilizadas (0,6±0,2 vs 0,8±0,2; P>0,05). Não houve diferença na produção de embriões quando do emprego de uma ou duas IATFs. / This study is presented in Chapter 1 (Superovulations protocols with FTAI for Bos taurus) and Chapter 2 (Superovulation protocols with FTAI for Bos indicus), in this Chapter are included three experiments [1 - Moment of the application of LH in cows Nelore (Bos indicus); 2 - Effect of the injectable progesterone administration in the day 0 in Nelore cows; 3 - Effect of the number of inseminations in superstimulated and fixed-time inseminated Nelore cows]. On Chapter 1, it went to evaluate the time of intravaginal P4 device (DIBTM) withdrawal and the application of LH in Holstein cows superstimulated with FTAI. Sixteen cows, treated with DIB (D-1) and 2mg of EB (D0) were assigned in four groups (superstimulation with 200mg of FSHp in 8 decreasing doses starting on D4). On D6, PGF was administered and the cows were accomplished in four groups: P24LH48; P24LH60; P36LH48 and P36LH60 (cross-over). The FTAIs were performed 12 and 24h after LH. The main effects for treatments P24 vs P36 and LH48vsLH60 were: ovulation rate (OR; 49.9&plusmn;5.7 vs 60.9&plusmn;4.8% and 53.1&plusmn;5.3 vs 57.5&plusmn;5.4%; P>0.05), total of structures (TS; 4.4&plusmn;0.9 vs 5.0&plusmn;0.9 and 3.8&plusmn;0.7 vs 5.7&plusmn;1.0; P>0.05), transferable embryos (TE; 3.0&plusmn;0.7 vs 4.1&plusmn;0.9 and 2.3&plusmn;0.5a vs 4.9&plusmn;0.9b; P<0.05) and suitable to freezing embryos (FE; 2.9&plusmn;0.7 vs 3.8&plusmn;0.8 and 2.1&plusmn;0.5a vs 4.7&plusmn;0.9b; P<0.05). The LH 60h after prostaglandin increased the TE and FE in Holstein cows. In the Chapter 2, it was studied different superstimulation with FTAI protocols in Nelore. In the first Experiment cows (n=20) were superovulated and treated with LH 48h (G-LH48) or 60h (G-LH60) after prostaglandin. There were no significant (P>0.05) differences in the variables between LH48 and LH60: number of follicles >8mm at the time of LH (FolLH12.5±1.5 and 9.4±1.0), OR [169/249 (71.0±4.2 %) and 120/187 (64.6±4.0%)]. However, there were differences (P<0.05) between G-LH48 and G-LH60 in the variables: interval first/last ovulation (IntOV15.0±2.1a and 21.0±1.7b), TS (7.5±1.0a and 5.1±0.5b), TE (6.2±1.0a and 3.1±0.5b), and FE (5.9±0.9a and 2.5±0.5b). The LH 48h after prostaglandin was more efficient in Nelore cows. In second experiment, ten Nelore cows were divided in two groups (D0): EB plus injectable progesterone group (G-BE+P4); or EB group (G-BE). The results for G-BE+P4 and G-BE were: follicular wave emergency in days (FE; 3.6&plusmn;0.2 and 4.0&plusmn;0.1; P>0.05), variation in FE [(2.5 to 4.5) and (3.5 to 4.5)], IntOV (32.4&plusmn;1.8 and 33.6&plusmn;1.6; P>0.05), TS (7.7&plusmn;0.8 and 9.2&plusmn;1.2; P>0.05), degenerated embryos (0.6&plusmn;0.2 and 0.8&plusmn;0.2; P>0.05), TE (6.2±0.6 e 7.2±1.1; P>0.05), and FE (5.1&plusmn;0.7 and 6.3&plusmn;1.0; P>0.05). The third Experiment, ten Nelore cows were divided in two groups: G-1IATF (16h after LH) or G-2IATF (12 and 24h after LH). The results for G-1IATF and G-2IATF were: FolLH (16.2&plusmn;1.4 and 14.8&plusmn;1.2; P>0.05), TS (8.2±0.9 and 7.2±0.8; P>0.05), TE (4.3±0.7 and 4.2±0.6; P>0.05), FE (2.9±0.6 and 2.8±0.4; P>0.05) and unfertilized structures (0.6&plusmn;0.2 and 0.8&plusmn;0.2; P>0.05). There was no difference on embryo production when the cows were inseminated one (16h) or two (12 and 24h) inseminations.