The physiology and impact on fertility of the period of proestrus in lactating dairy cows

In cattle, proestrus begins with the initiation of luteolysis and ends with initiation of estrus and the GnRH/LH surge. This period is marked by a dramatic decrease in circulating progesterone (P4 ) that reaches a nadir by about 36-48 h in cows undergoing natural or prostaglandin F2α (PGF )-induced luteolysis. Inadequate luteolysis is a cause of reduced fertility particularly in timed AI programs with small elevations in circulating P4 reducing fertility. Increasing circulating estradiol ( E2 ) during proestrus is dependent on presence, size, and function of the dominant follicle and this varies during natural proestrus, due to whether animals have two or three follicular waves, and during PGF-induced proestrus, according to stage of the follicular wave at time of PGF treatment. Inadequate circulating E2 can limit fertility and increase pregnancy loss in some specific circumstances such as in cows with low BCS and in cows during heat stress. Thus, studies to optimize the length of proestrus and the concentrations of E2 and P4 during proestrus could produce substantial improvements in fertility and reductions in pregnancy loss.

The physiology and impact on fertility of the period of proestrus in lactating dairy cows

In cattle, proestrus begins with the initiation of luteolysis and ends with initiation of estrus and the GnRH/LH surge. This period is marked by a dramatic decrease in circulating progesterone (P4 ) that reaches a nadir by about 36-48 h in cows undergoing natural or prostaglandin F2α (PGF )-induced luteolysis. Inadequate luteolysis is a cause of reduced fertility particularly in timed AI programs with small elevations in circulating P4 reducing fertility. Increasing circulating estradiol ( E2 ) during proestrus is dependent on presence, size, and function of the dominant follicle and this varies during natural proestrus, due to whether animals have two or three follicular waves, and during PGF-induced proestrus, according to stage of the follicular wave at time of PGF treatment. Inadequate circulating E2 can limit fertility and increase pregnancy loss in some specific circumstances such as in cows with low BCS and in cows during heat stress. Thus, studies to optimize the length of proestrus and the concentrations of E2 and P4 during proestrus could produce substantial improvements in fertility and reductions in pregnancy loss.(AU)

Relationships between growth of the preovulatory follicle and gestation success in lactating dairy cow

This report summartizes three studies conducted with lactating dairy cws aiming to increase pregnancy rates to fixes time artificial insemination (TAI) protocols. Experiment I was designed to determine if changing the the timing of PGF2α treatment during an E2/P4 based program would affect fertility to TAI or fixedtime embryo transfer (TET). In experiment 2, pregnancy rates to AI were compared following synchronized ovulation using two protocols that have been developed to reduce the period between follicular wave emergence and TAI. The Ovsynch type protocol utilizes GnRH to synchronize the follicular wave by inducing ovulati on of a dominant follicle at the beginning of the protocol, and to synchronize ovulation at the end of the protocol allowing TAI. In contrast, E2/P4 based protocols utilize E2 products in the presence of P4 to induce atresia of antral follicles and synchro nize emergence of a new follicular wave. At the end of E2/P4 based protocol another E2 treatment in the absence of P4 is used to induce LH release and synchronize ovulation and allow TAI. Experiment 3 was designed to determine whether increasing the length time interval with reduced circulating P4 (proestrus) would increase fertility in a TAI program that utilized E2 and P4 to synchronize ovulation of cycling, lactating dairy cows. The overall conclusions are that circulating concentrations of progesterone and estradiol prior to and circulating concentrations of progesterone following ovulation can affect fertility in cattle. In addition, small increases in P4 concentrations near the time of AI, due to lack of complete CL regression, result in reductions in fertility. Earlier treatment with PGF2α should allow greater time for CL regression, an increase in estradiol and subsequent reductions in circulating P4 that could be critical for fertility. Optimization of follicle size in TAI programs is clearly an intr icate balance between oocyte quality, adequate circulating E2 near AI, and adequate circulating P4 after AI.

Relationships between growth of the preovulatory follicle and gestation success in lactating dairy cow

This report summartizes three studies conducted with lactating dairy cws aiming to increase pregnancy rates to fixes time artificial insemination (TAI) protocols. Experiment I was designed to determine if changing the the timing of PGF2α treatment during an E2/P4 based program would affect fertility to TAI or fixedtime embryo transfer (TET). In experiment 2, pregnancy rates to AI were compared following synchronized ovulation using two protocols that have been developed to reduce the period between follicular wave emergence and TAI. The Ovsynch type protocol utilizes GnRH to synchronize the follicular wave by inducing ovulati on of a dominant follicle at the beginning of the protocol, and to synchronize ovulation at the end of the protocol allowing TAI. In contrast, E2/P4 based protocols utilize E2 products in the presence of P4 to induce atresia of antral follicles and synchro nize emergence of a new follicular wave. At the end of E2/P4 based protocol another E2 treatment in the absence of P4 is used to induce LH release and synchronize ovulation and allow TAI. Experiment 3 was designed to determine whether increasing the length time interval with reduced circulating P4 (proestrus) would increase fertility in a TAI program that utilized E2 and P4 to synchronize ovulation of cycling, lactating dairy cows. The overall conclusions are that circulating concentrations of progesterone and estradiol prior to and circulating concentrations of progesterone following ovulation can affect fertility in cattle. In addition, small increases in P4 concentrations near the time of AI, due to lack of complete CL regression, result in reductions in fertility. Earlier treatment with PGF2α should allow greater time for CL regression, an increase in estradiol and subsequent reductions in circulating P4 that could be critical for fertility. Optimization of follicle size in TAI programs is clearly an intr icate balance between oocyte quality, adequate circulating E2 near AI, and adequate circulating P4 after AI.(AU)

O uso de FSH exógeno estimula o crescimento folicular final e a função luteínica de vacas Holandesas em lactação sincronizadas para Inseminação Artificial em Tempo Fixo? / Does exogenous FSH increase the final follicular growth and lutea function for TAI in lactating Holstein cows?

Vacas leiteira de alta produção têm apresentado declínio da eficiência reprodutiva. Essa redução é devido a causas multifatoriais, entre elas a baixa concentração de estradiol (E2) no proestro e a baixa concentração de progesterona (P4) no ciclo estral subsequentente. O objetivo deste trabalho foi comparar o uso de gonadotrofina exógena na dinâmica folicular e na taxa de prenhez de vacas submetidas ao protocolo Ovsynch (Experimento 1) ou a protocolos utilizando P4 e E2 (Experimento 2). No Experimento 1, animais de primeiro serviço foram pré-sincronizados com dois protocolos (Presynch ou Double-Ovsynch). Já os animais de segundo ou mais serviços foram resincronizados com o protocolo Resynch. Os animais receberam GnRH (1º GnRH), seguido 7 dias depois pela adiministração de prostaglandina F2α (PGF2α). Nesse momento os animais foram divididos homogeneamente por paridade e número de inseminação em um de dois tratamentos: sem FSH (Ovsynch, n = 561) ou com FSH (Ovsynch + FSH, n = 571). O segundo GnRH (2º GnRH) foi administrado 56 horas após a PGF2α e a inseminação em tempo fixo foi realizada 16 horas após. Amostras de sangue foram colhidas no 1º e no 2º GnRH, na PGF2α e 6 e 13 dias após o 2º GnRH para dosagem de P4. Ainda, no 2º GnRH dosou-se também E2 No Experimento 2, os animais foram sincronizados no dia 0 com um dispositivo de P4 associado a 2 mg de benzoato de estradiol. Oito dias após o dispositivo foi removido e os animais receberam uma dose de PGF2α. Neste mesmo momento, as vacas foram divididas homogeneamente por paridade, número de serviços prévios, escore de condição corporal e presença de CL no inicio do protocolo em três tratamentos: Controle (sem tratamento adicional; n = 232); eCG (400 UI de eCG; n = 232) e FSH (20 mg de FSH; n = 230). Todos os animais receberam GnRH e foram insemados 56h após a retirada do dispositivo. Foram colhidas amostras de sangue a cada 48h do dia 11 ao dia 22. No Experimento 1, não houve efeito do FSH na concetração sérica de E2 no 2º GnRH (P = 0,88), no tamanho do maior folículo no 2 º GnRH (P = 0,63), na taxa de ovulação ao 2º GnRH (P = 0,69) ou na concentração sérica de P4 no 6º (P = 0,15) e 13º (P = 0,36) dia após o 2º GnRH. A taxa de prenhez foi semelhante (P> 0,05) entre os animais tratados com Ovsynch (36,2%) e Ovsynch + FSH (39,1%). No Experimento 2, os tratamentos não alteraram o diâmetro do folículo ovulatório (P = 0,15), o intervalo entre a remoção do dispositivo de P4 e a ovulação (P = 0,30) e a taxa de ovulação (P = 0,44). Não houve efeito de tratamento na concentração sérica de P4 (P = 0,15). A taxa de prenhez foi diferente entre os tratamentos aos 30 dias após a IATF (Controle = 28,0a vs FSH = 18,7b vs eCG = 29,7a %; P = 0,01), mas não aos 60 dias (Controle = 21,6 vs FSH = 16,1 vs eCG = 24,1%; P = 0,08) e na perda de gestacional (Controle = 18,8 vs FSH = 14,0 vs eCG = 18,4%; P = 0,39). Assim, o tratamento com FSH não estimulou o crescimento folicular final e a função luteínica de vacas leiteiras de alta produção sincronizadas com os protocolos Ovsynch e P4/E2

Fertility in high-producing dairy cows has decreased over the years, which has been associated with reduced estradiol (E2) concentrations during proestrus and suboptimal progesterone (P4) concentrations during early stages of gestation. The objectives of the present study were to evaluate the effects of exogenous gonadotropins on follicular dynamics and risk of pregnancy per artificial insemination (P/AI) in cows subjected to the Ovsynch protocol (Experiment 1) or to a P4/E2-based timed AI protocol (experiment 2). In experiment 1, cows were enrolled in the Ovsynch protocol (GnRH, 7 d PGF2α, 56 h GnRH, 16 h IA) either after presynchronization (Presynch or Double-Ovsynch; first AI postpartum) or 32 d after previous AI. At the PGF2α injection, cows were blocked by parity and number of AI and, within each block, randomly allocated to eitherreceive 20 mg of FSH at the moment of the PGF2α(Ovsynch + FSH, n = 571) or to remain as untreated control (Ovsynch, n = 561). Blood was sampled at the 1st and 2nd GnRH and PGF2α injections, as well as on d 6 and 13 after the 2nd GnRH to access P4 and E2 (at the 2nd GnRH only) concentrations. In experiment 2, cows were received a P4 device and 2 mg of estradiol benzoate. The device was removed 8 d later concurrently with an injection of PGF2α, followed by an injection of GnRH and AI at 56 h.At the PGF2α injection, cows were blocked by parity, number of AI, body condition score, and presence of a CL at device insertion.Within each block, cows were randomly allocated to receive either 20 mg of FSH (FSH, n = 230), 400 IU of eCG (eCG, n = 232), or no additional treatment at the moment of the PGF2α (Control, n = 232). Blood was sampled at every 48 h from 1 to 12 d after AI. In experiment 1, there was no effect of FSH on serum E2 at the 2nd GnRH (P = 0.88), follicle diameter at the 2nd GnRH (P = 0.63), ovulatory response to the 2nd GnRH (P = 0.69), or serum P4 on d 6 (P = 0.15) and 13 (P = 0.36) after the 2nd GnRH. Also, P/AI was similar (P > 0.05) between Ovsynch (36.2%) and Ovsynch + FSH (39.1%). In experiment 2, treatment did not affect ovulatory diameter (P = 0.15), interval from P4 device removal and ovulation (P = 0.30), ovulatory response to the 2nd GnRH (P = 0.44), and serum P4 (P = 0.15). Interestingly, treatment with FSH reduced (P = 0.01) P/AI on d 30 (Control = 28.0a vs. FSH = 18.7b vs. eCG = 29.7a %), but not on d 60after timed AI (Control = 21.6 vs. FSH = 16.1 vs. eCG = 24.1%; P = 0.08).The risk of pregnancy loss was not affected by treatment (Control = 18.8 vs. FSH = 14.0 vs. eCG = 18.4%; P = 0.39). In conclusion, treatment with FSH failed to enhance the final growth of the ovulatory follicle and did not improve luteal function after AI in high-producing dairy cows synchronized with either the Ovsynch or P4/E2-based timed AI protocols