Pre-TAI protocol strategies to increase reproductive efficiency in beef and dairy cows

Ovulation synchronization protocols are well established in beef and dairy cows. However, the protocol response rate is around 70-90%. In beef cows, factors such as inadequate nutrition and calf presence negatively impact the response of progesterone (P4)/estradiol-based ovulation synchronization protocols by interfering with GnRH release and consequently reducing LH pulsatility and final follicular development. In dairy cows, protocols based on GnRH and prostaglandin (Ovsynch) are the most widely used in the world. However, the efficiency of Ovsynch is dependent on the presence of a large follicle at the time of administration of the first GnRH. In these ovulation synchronization protocols, pre-synchronization protocols (Prostaglandins, Double Ovsynch and P4synch) are usually attempted in an effort to increase responses. Thus, the objective of this review was to discuss pre-ovulation synchronization strategies (administration of injectable P4 or energetic/protein supplementation or presynchronization with intra-vaginal progesterone devices) aiming to increase the LH pulsatility in beef cows or induce the formation of a GnRH-responsive follicle at the beginning of the Ovsynch protocol in dairy cows.

Pre-TAI protocol strategies to increase reproductive efficiency in beef and dairy cows

Ovulation synchronization protocols are well established in beef and dairy cows. However, the protocol response rate is around 70-90%. In beef cows, factors such as inadequate nutrition and calf presence negatively impact the response of progesterone (P4)/estradiol-based ovulation synchronization protocols by interfering with GnRH release and consequently reducing LH pulsatility and final follicular development. In dairy cows, protocols based on GnRH and prostaglandin (Ovsynch) are the most widely used in the world. However, the efficiency of Ovsynch is dependent on the presence of a large follicle at the time of administration of the first GnRH. In these ovulation synchronization protocols, pre-synchronization protocols (Prostaglandins, Double Ovsynch and P4synch) are usually attempted in an effort to increase responses. Thus, the objective of this review was to discuss pre-ovulation synchronization strategies (administration of injectable P4 or energetic/protein supplementation or presynchronization with intra-vaginal progesterone devices) aiming to increase the LH pulsatility in beef cows or induce the formation of a GnRH-responsive follicle at the beginning of the Ovsynch protocol in dairy cows.(AU)

Efeito da aplicação de benzoato de estradiol ou da Gonadotrofina Coriônica humana em protocolos de ressincronização da ovulação sobre a prenhez da IATF / Effects of estradiol benzoate or human Chorionic Gonadotropin for ovulation resynchronization protocols on pregnancy rate per TAI

Background: Programs of resynchronization of ovulation have the objective of allowing reinsemination of females that did not get pregnant after fixed time artificial insemination (TAI), in the lowest time interval possible. These protocols are usually composed of administration of estradiol benzoate (EB) concomitant to the insert of progesterone-based (P4) intravaginal implants 22 to 24 days after the first TAI. However, little information is available on the impact of hormonal manipulation in a pre-established pregnancy. The objective of this study was to evaluate if resynchronization of ovulation, started 24 days after the first TAI, would interfere in the function of the corpus luteum (CL), production of P4, and pre-established pregnancy.Materials, Methods & Results: For this study, 526 Brangus heifers with ages between 24 and 26 months, were subjected to TAI program in the beginning of the breeding season. Synchronization protocol for the first TAI started with insertion of an intravaginal implant containing 750 mg of P4 and administration of 2 mg of estradiol benzoate (EB) intramuscular (im) on day -9 (D-9). After seven days (D-2), P4 implants were removed, and 150 µg of D-cloprostenol (PGF), i.m., and 1 mg of estradiol cypionate (EC), i.m., were administered. The TAI was performed between 48 and 54 h after removal of the P4 implant (D0). Twenty-four days after the first TAI (D24), heifers were randomly divided into the following experimental groups: Control (n = 167, no treatment), EB (n = 208, 1 mg of EB, i.m.), and hCG (n = 151, 1000 IU of hCG, i.m.). Heifers of EB and hCG groups received a new intravaginal device containing 750 mg of P4 on D24. On day 31 (D31), P4 implants were removed and pregnancy diagnosis were performed by ultrasound. Pregnancy rates from the first TAI on D31 were 58.7% (98/167), 53.4% (111/208) and 52.9% (80/151) respectively for groups Control, EB and hCG.[...](AU)

Efeito da aplicação de benzoato de estradiol ou da Gonadotrofina Coriônica humana em protocolos de ressincronização da ovulação sobre a prenhez da IATF / Effects of estradiol benzoate or human Chorionic Gonadotropin for ovulation resynchronization protocols on pregnancy rate per TAI

Background: Programs of resynchronization of ovulation have the objective of allowing reinsemination of females that did not get pregnant after fixed time artificial insemination (TAI), in the lowest time interval possible. These protocols are usually composed of administration of estradiol benzoate (EB) concomitant to the insert of progesterone-based (P4) intravaginal implants 22 to 24 days after the first TAI. However, little information is available on the impact of hormonal manipulation in a pre-established pregnancy. The objective of this study was to evaluate if resynchronization of ovulation, started 24 days after the first TAI, would interfere in the function of the corpus luteum (CL), production of P4, and pre-established pregnancy.Materials, Methods & Results: For this study, 526 Brangus heifers with ages between 24 and 26 months, were subjected to TAI program in the beginning of the breeding season. Synchronization protocol for the first TAI started with insertion of an intravaginal implant containing 750 mg of P4 and administration of 2 mg of estradiol benzoate (EB) intramuscular (im) on day -9 (D-9). After seven days (D-2), P4 implants were removed, and 150 µg of D-cloprostenol (PGF), i.m., and 1 mg of estradiol cypionate (EC), i.m., were administered. The TAI was performed between 48 and 54 h after removal of the P4 implant (D0). Twenty-four days after the first TAI (D24), heifers were randomly divided into the following experimental groups: Control (n = 167, no treatment), EB (n = 208, 1 mg of EB, i.m.), and hCG (n = 151, 1000 IU of hCG, i.m.). Heifers of EB and hCG groups received a new intravaginal device containing 750 mg of P4 on D24. On day 31 (D31), P4 implants were removed and pregnancy diagnosis were performed by ultrasound. Pregnancy rates from the first TAI on D31 were 58.7% (98/167), 53.4% (111/208) and 52.9% (80/151) respectively for groups Control, EB and hCG.[...]

Administration of human chorionic gonadotropin to improve luteal function in lactating beef cattle / Administração de gonadotrofina coriônica humana para estimulação da função luteal em vacas de corte lactantes

Background: Pregnancy rate after fixed-time artificial insemination (FTAI) in beef cattle is affected by ovulation rate,luteal function and embryo survival. Cows in early post partum period frequently have low progesterone productionand short luteal phases. Treatments using human chorionic gonadotropin (hCG) after FTAI have been tested in aneffort to increase progesterone concentration, improve embryo development and consequently pregnancy rates. Theobjectives of this work were to evaluate the effects of administration of hCG on day 4 after FTAI on induction ofovulation of the first dominant follicle, corpus luteum (CL) development, progesterone production and pregnancyrate in lactating beef cows.Materials, Methods & Results: Five hundred and sixty nine multiparous Angus suckled beef cows, 45-70 dayspostpartum, were synchronized to FTAI. On day -9, intravaginal implants containing 0,750 g of progesterone wereinserted and 2mg of estradiol benzoate administered, im. Seven days later, cows had their implants removed andwere injected with 150 µg of d-cloprostenol, im, and 1 mg of estradiol cipionate, im. Cows were inseminated 52-56h after implant removal. Four days later, cows were assigned into two groups, hCG (1500 UI of hCG, im, n = 269) orControl (1,5 mL saline, im, n = 300). Blood samples were collected on days 4, 7, 10 and 14 after FTAI for analysisof serum progesterone concentration by radioimmunoassay. Ovarian ultrasonographic exams were done on day 0 todetermine the diameter of ovulatory follicle (OF), on day 4 to measure the diameter of the first dominant follicle and,on day 7, to determine the CL area (cm2) and the number of accesory CL. Pregnancy diagnosis were done on day 30.Pregnancy rates were compared by chi-square test, progesterone concentration and CLs parameters were comparedby student-t test. The administration of hCG resulted in higher serum progesterone concentration, improved CL areaand the frequency of accessory CL...

Administration of human chorionic gonadotropin to improve luteal function in lactating beef cattle / Administração de gonadotrofina coriônica humana para estimulação da função luteal em vacas de corte lactantes

Background: Pregnancy rate after fixed-time artificial insemination (FTAI) in beef cattle is affected by ovulation rate,luteal function and embryo survival. Cows in early post partum period frequently have low progesterone productionand short luteal phases. Treatments using human chorionic gonadotropin (hCG) after FTAI have been tested in aneffort to increase progesterone concentration, improve embryo development and consequently pregnancy rates. Theobjectives of this work were to evaluate the effects of administration of hCG on day 4 after FTAI on induction ofovulation of the first dominant follicle, corpus luteum (CL) development, progesterone production and pregnancyrate in lactating beef cows.Materials, Methods & Results: Five hundred and sixty nine multiparous Angus suckled beef cows, 45-70 dayspostpartum, were synchronized to FTAI. On day -9, intravaginal implants containing 0,750 g of progesterone wereinserted and 2mg of estradiol benzoate administered, im. Seven days later, cows had their implants removed andwere injected with 150 µg of d-cloprostenol, im, and 1 mg of estradiol cipionate, im. Cows were inseminated 52-56h after implant removal. Four days later, cows were assigned into two groups, hCG (1500 UI of hCG, im, n = 269) orControl (1,5 mL saline, im, n = 300). Blood samples were collected on days 4, 7, 10 and 14 after FTAI for analysisof serum progesterone concentration by radioimmunoassay. Ovarian ultrasonographic exams were done on day 0 todetermine the diameter of ovulatory follicle (OF), on day 4 to measure the diameter of the first dominant follicle and,on day 7, to determine the CL area (cm2) and the number of accesory CL. Pregnancy diagnosis were done on day 30.Pregnancy rates were compared by chi-square test, progesterone concentration and CLs parameters were comparedby student-t test. The administration of hCG resulted in higher serum progesterone concentration, improved CL areaand the frequency of accessory CL...(AU)

Análise da soroprevalência do herpesvírus bovino Tipo -1 e do cortisol sérico em diferentes situações de manejo no Rio Grande do Sul / Analisys of serum prevalence of bovine herpesvirus type 1 and seric cortisol in different situations of manegement in Rio grande do Sul state

Levando-se em conta que a eficiência reprodutiva é sumamente importante para uma maior produtividade em rebanhos de cria, foram pesquisados alguns tópicos correlacionados com o assunto em quatro artigos. Neles, estudou-se as variações de cortisol sérico frente a diferentes situações de manejo, a soroprevalência e dinâmica do BHV-1 em diferentes categorias animais em gado de corte e taxas de prenhez e abortos em rebanhos comerciais de gado de corte. O artigo 1 avaliou os níveis de cortisol sérico de bovinos de corte, em diferentes idades, frente a situações de manejo em um sistema de produção no Rio Grande do Sul. As concentrações de cortisol sérico foram determinadas por radioimunoensaio. Os níveis de cortisol sérico nas terneiras de 80 dias de idade (0,22±0,25 ug/dl) diferiram significativamente de todas as categorias (P<0,001), com exceção das terneiras de 180 dias (P=0,81). As terneiras com 180 dias (0,91±0,43 ug/dl) não diferiram das novilhas de um ano e dois anos (1,97±1,40 ug/dl e 2,15±1,41 ug/dl, respectivamente), mas diferiram das vacas. As novilhas nas duas idades não diferiram das vacas de três até oito anos de idade (3,25±1,89 ug/dl; 2,62±1,27 ug/dl; 2,42±0,93 ud/dl; 3,12±0,69 ug/dl; 2,89±0,41 ug/dl; 2,12±1,22 ug/dl, respectivamente). Os touros de um ano (1,00±0,73 ug/dl), de dois anos (0,89±0,43 ug/dl) e três anos (1,44±0,60 ug/dl) diferiram estatisticamente das terneiras de 80 dias de idade e das vacas. Ao aplicar para as fêmeas, o coeficiente de correlação de Pearson, determinou-se um valor entre as diferentes idades de r=0,48 ug/dl, indicando que o cortisol sérico eleva-se, nelas cerca de 0,48 ug/dl para cada acréscimo de um ano na idade. Frente a uma situação evidente de estresse (castração), o cortisol sérico variou cinco vezes, indo de 0,66 ug/dl para 3,36 ug/dl.Estes resultados indicam que há uma variação de cortisol sérico com a idade em bovinos de corte, e que este hormônio pode elevar-se diante de uma situação de estresse. O artigo 2 determinou as taxas fisiológicas do cortisol sérico em terneiras aberdeen angus e examinou as variações que ocorreram em função de dois diferentes tipos de desmame. Utilizou-se dois grupos de terneiras, um deles (n=24) submetido ao desmame com 90 dias pós-parto (desmame precoce) e o outro (n=24) submetido ao desmame com 210 dias (tradicional). Para avaliar as variações do cortisol sérico pós-desmame, foram feitas coletas 24, 48, 72 e 168 horas pós-desmame. As determinações foram feitas por radioimunoensaio. Os animais foram pesados aos 90, 210, 365 e 730 dias para avaliar o ganho de peso nos dois grupos. O desempenho reprodutivo dos animais foi acompanhado pela análise das taxas de prenhez e de perdas de conceptos até o primeiro parto previsto. Os resultados mostraram que os valores de cortisol sérico no grupo precoce, elevaram-se de 0,22±0,25 ug/dl em níveis basais antes do desmame para 0,71±0,64 ug/dl nas 24 horas pós-desmame, baixando para 0,26±0,30 ug/dl em uma semana. No grupo tradicional elevaram-se de 0,91±0,43 ug/dl em níveis basais antes do desmame para 1,94±0,89 ug/dl nas 24 horas, baixando para 0,99±0,46 ug/dl em uma semana. O trabalho mostrou que: houve elevação nos níveis séricos de cortisol nas primeiras 24 horas pós-desmame, os quais retornaram aos níveis fisiológicos após uma semana em ambos os grupos; o grupo desmamado tradicionalmente teve um ganho de peso significativamente superior (P<0,001) ao grupo desmamado precocemente; no desempenho reprodutivo não houve diferenças significativas nas taxas de prenhez e de perdas. O artigo 3 estimou a soroprevalência de anticorpos contra o BHV-1 em animais não vacinados e determinou a chance de apresentarem a infecção, em diversas categorias, de um rebanho de cria em uma propriedade de criação extensiva no Rio Grande do Sul. Amostras sorológicas de 1.516 animais, de um total de 2.600, foram coletadas. A pesquisa de anticorpos foi realizada através de soroneutralização. Os dados dos animais foram registrados e analisados com o auxílio do programa SPSS 12.0. Em todas as categorias ocorreram animais soropositivos e a soroprevalência nesta propriedade foi de 29,22%. Nos bovinos com mais de três anos chegou a 62,38%. Cabe salientar que, após o primeiro serviço, nas novilhas de dois anos, a soroprevalência para o BHV-1 aumentou dez vezes indo de 3,85% para 38,5%. A soroprevalência aumenta conforme a idade de forma significativa (P<0,001) após os dois anos, e o período reprodutivo aumenta as chances que os bovinos têm de apresentarem a infecção.No artigo 4 foram avaliadas as taxas de prenhez e de perdas, até o parto, em propriedades rurais que utilizam ou não, uma vacina que protege para doenças reprodutivas no Rio Grande do Sul. Foram selecionadas onze propriedades em seis municípios do litoral norte. Foi utilizada vacina em quatro propriedades. Acompanhou-se 27.774 vacas (13.477 vacinadas e 14.297 não vacinadas) por quatro temporadas reprodutivas (2001-2004). Na reprodução, utilizou-se inseminação artificial e repasse com touros. Os dados foram coletados nas propriedades e analisados com o auxílio do programa SPSS, versão 12.0. O índice geral de prenhez das vacas vacinadas foi de 72,7% e das vacas não vacinadas foi de 70,4%. Esta diferença considerando as 27.774 foi estatisticamente significativa (P<0,001). A taxa de perdas (abortos) das vacas vacinadas foi de 2,38% e das vacas não vacinadas, de 2,98%. Esta diferença, considerando um total de 19.865 vacas prenhas foi estatisticamente significativa (P=0,004)

Once reproductive efficiency is extremely important to a higher productivity in breedings herds, some issues related to this subjet were discussed in four articles. Variation on serum cortisol levels under stressful situations, seroprevalence and dynamics of BHV-1 in different animal categories of beef cattle, pregnancy and abortion rates in commercial herds were the topics studied in the articles. The first study evaluated levels of serum cortisol in animals of different ages, submitted to stressful conditions. Serum cortisol levels were evaluated in 80 and 180 days calves, 1 and two year old heifers, cows ranging from 3 to 8 years , and in bulls of 1, 2 and 3 years, as well as in 3 year males submitted to castration. Blood samples were collected always in the mornings, because hormones like cortisol have cicardian variation. Cortisol levels were determinated by radioimmunoassay. Calves with 80 days of age (22¿g/dl±0,25¿/dl) had serum levels statistic different (p<0,001) from all the other categories, except for 180 days calves (P=0,81); 180 days calves( 0,91±0,43 ug/dl)did not differ from the one and two year heifers ( 1,97±1,40 ug/dl and 2,15±1,41 ug/dl, respectively), but had levels statistically different from all the other cows .Heifers in both ages did not differ from cows from 3 to 8 years (3,25±1,89 ug/dl; 2,62±1,27 ug/dl; 2,42±0,93 ud/dl; 3,12±0,69 ug/dl; 2,89±0,41 ug/dl; 2,12±1,22 ug/dl, respectivelly). The bulls at one ( 1,00±0,73 ug/dl), two ( 0,89±0,43 ug/d), and three years old (1,44¿g/dl±0,60 ug/dl) had levels statistically different from the 80 days calves and cows. Using Pearson correlation for the females, the value for different ages was r=0,48¿g/dl, indicating that serum cortisol enhances 0,48¿g/dl for each year of age. In a stressful situation, serum cortisol enhanced five times, ranging from 0,66 ¿g/dl to 3,36 ¿g/dl. These results suggest that serum cortisol changes with age, and that this hormone may be useful to demonstrate an stressful situation in beef cattle. The second study aimed to determine physiologic values for serum cortisol in Aberdeen angus calves and to examine whether different weaning schedules would have any effect on such values. Two groups of calves were studied: the first group (n=24) comprised calves submitted to weaning at 90 days of age (early weaning); the second group (n=24) comprised calves submitted to weaning at 210 days of age (traditional weaning).Serum samples were colleted before weaning on day 80 (calves on early weaning) and on day 180 (calves on traditional weaning) to determine basal cortisol levels. To evaluate serum cortisol levels after weaning, blood samples were collected at 24, 48, 72 and 168 hours after weaning, always in the mornings, because of cicardian rhythm. Serum cortisol concentration was measured by radioimmunoassay method. Average daily gain at 90, 210, 365 and 730 days was measures in both groups.Pregnancy rate and losses until parturition were the parameters used to evaluate reproductive performance. Data showed that basal serum cortisol (0,22±0,25 ug/dl) in the early weaning group enhanced to 0,71±0,64 ug/dl in the first 24 hours after weaning, reducing to 0,26±0,30 ug/dl after a week. In the traditional weaning group, basal leves (0,91±0,43 ug/dl) enhanced to1,94±0,89 ug/dl in the first 24 hours, and reduced to 0,99±0,46 ug/dl in a week. This study showed that serum cortisol levels enhanced in the first 24 hours after weaning for both groups, returning to basal levels in a week The traditional weaning group had higher average daily gain (P<0,001).No significant differences were observed for pregnancy rates and losses until parturition. The third study had the objective of estimating antibody presence against BHV- 1 in non vaccinated animals, and evaluate the chance of animal developing infection in several categories in beef cattle herd in Rio Grande do Sul. Sorologic samples of 1516 animals, from a total of 2600, were collected between March 2003 and October 2005. Antibody presence was determinated by seroneutralization. Data was registered and analysed with SPSS 12.0. For comparative analysis, Fisher test was used and odds ratio was determinated with 95% confidence. Antibody presence in the herd was 29,22%, with seropositive animals in all categories. Serum prevalence was of 62,38% in three year old cows. Antibody prevalence inhanced 10 times after first service in the 2 yr heifers, turning from 3,85 % to 38,5%. Antibody presence enhances with age (P<0,001), specially after two years old, and chances of developing infection is higher after breeding season. The fourth study was conducted to evaluate pregnancy rates and losses until parturition (abortion) in farms, that either use a reproductive vaccine or not. In the vaccinated herds, a commercial vaccine was used. Eleven herds were selected, and vaccination was done in four of these herds. A total of 27774 cows were analysed, with 13477 cows routinely vaccinated and the other 14297 cows not vaccinated, for four breeding seasons (2001-2004). The cows were bred AI and exposed to a fertile bull. Data was collected in the farms, and analysed with SPSS 12.0. Total pregnancy rate was 72,7% in the group of vaccinated cows and 70,4% in the non vaccinated. This diference, considering the total 27774 cows was statiscally significant (p<0,001). Abortion rate was 2,38% in the vaccinated vs 2,98% in the non vaccinated group, and was statistically different (p=0,004). These results indicate that vaccinated herds had higher pregnancy rates and less losses by abortion