Synchronization of ovulation in crossbred dairy heifers using gonadotrophin-releasing hormone agonist, prostaglandin F2<FONT FACE=Symbol>a</FONT> and human chorionic gonadotrophin or estradiol benzoate

Girolando (Gir x Holstein) is a very common dairy breed in Brazil because it combines the rusticity of Gir (Bos indicus) with the high milk yield of Holstein (Bos taurus). The ovarian follicular dynamics and hormonal treatments for synchronization of ovulation and timed artificial insemination were studied in Girolando heifers. The injection of a gonadotrophin-releasing hormone (GnRH) agonist was followed 6 or 7 days (d) later by prostaglandin F2<FONT FACE="Symbol">a</FONT> (PGF2<FONT FACE="Symbol">a</FONT>). Twenty-four hours after PGF2<FONT FACE="Symbol">a</FONT> injection either human chorionic gonadotropin (hCG, GPh-d6 and GPh-d7 groups) or estradiol benzoate (EB, GPE-d6 and GPE-d7 groups) was administered to synchronize ovulation and consequently allow timed artificial insemination (AI) 24 and 30 h after hCG and EB injection, respectively. Follicular dynamics in Girolando heifers was characterized by the predominance of three follicular waves (71.4%) with sizes of dominant follicles (10-13 mm) and corpus luteum (approximately 20 mm) similar to those for Bos indicus cattle. In the GnRH-PGF-hCG protocol, hCG administration induced earlier ovulation (67.4 h, P<0.01) compared to the control group (GnRH-PGF) and a better synchronization of ovulation, since most of it occurred within a period of 12 to 17 h. Pregnancy rate after timed AI was 42.8 (3/7, GPh-d6) to 50% (7/14, GPh-d7). In contrast, estradiol benzoate (GnRH-PGF-EB protocol) synchronized ovulation of only 5 of 11 heifers from the GPE-d7 group and of none (0/7) from the GPE-d6 group, which led to low pregnancy rates after timed AI (27.3 and 0%, respectively). However, since a small number of Girolando heifers was used to determine pregnancy rates in the present study, pregnancy rates should be confirmed with a larger number of animals

Avaliação ultra-sonográfica da dinâmica folicular e lútea em vacas da raça Guzerá Ultrasonographic evaluation of follicular dynamics and luteal function in Guzerá cows

Caracterizaram-se o padrão de crescimento folicular e a função lútea ao longo do ciclo estral em vacas da raça Guzerá (n=5), multíparas, não-lactantes. Os animais utilizados apresentavam idade e condição corporal semelhantes e peso corporal médio de 518± 48.5kg. A dinâmica folicular foi monitorada diariamente a partir do dia da ovulação, durante dois ciclos consecutivos, utilizando-se um aparelho de ultra-sonografia equipado com uma probe linear retal de 5MHz. Amostras de sangue foram coletadas a cada 48h, a partir do momento da ovulação, durante os dois ciclos. O primeiro ciclo foi sincronizado pela administração de um luteolítico (cloprostenol), e o segundo foi natural. Os folículos foram identificados e mensurados; e os dados obtidos, registrados em função do dia do ciclo. O comprimento do ciclo estral foi de 19,10± 1,86 dias. Observou-se maior incidência de ciclos com três ondas de crescimento folicular (50%), mas ciclos com duas (37,5%) ou quatro ondas (12,5%) também foram identificados. O diâmetro máximo dos folículos dominantes não ovulatórios foi de 11,60± 2,37 mm, e dos folículos ovulatórios de 14,4± 0,5 mm. A taxa de crescimento dos folículos dominantes da primeira, segunda, terceira e quarta onda foi de 1,48± 0,60; 0,81± 0,13; 1,10± 0,27 e 1,33mm/dia, respectivamente. A concentração máxima de progesterona no diestro foi de 5,50± 0,92ng/ml. A raça Guzerá apresenta características da dinâmica folicular semelhantes àquelas observadas em outras raças zebuínas, como a tendência ao maior número de ondas de crescimento associadas à menor taxa de crescimento, diâmetro máximo e persistência dos folículos dominantes das ondas intermediárias.<br>The follicular growth pattern and luteal function during the estrous cycle were studied using multiparous, non-lactating Guzerá cows (n=5). The animals presented similar age, body score condition, and mean body weight of 518 ± 48.5kg. Follicular dynamics was daily monitored between ovulations during two consecutive estrous cycles, using an ultrasound device equipped with a linear rectal 5MHz transducer. Blood samples were collected each 48h after ovulation, during the evaluated cycles. The first cycle was synchronized using a luteolytic agent (cloprostenol), and the second estrous cycle was natural. Follicles were identified and measured, and data were individually recorded according to the day of the cycle. The mean length of the cycles was 19.10 ± 1.86 days. There was a higher incidence of cycles presenting three follicular growth waves (50%), but cycles presenting two (37.5%) or three (12.5%) waves were also observed. The maximum diameter of non-ovulatory follicles was 11.60± 2.37mm, and that of ovulatory follicles was 14.40± 0.50mm. The growth rate of dominant follicles during the first, second, third and fourth waves were 1.48 ± 0.60; 0.81 ± 0.13; 1.10 ± 0.27 and 1.33mm/day, respectively. Progesterone maximum concentration during diestrus was 5.50± 0.92ng/ml. These results show that the Guzera breed presents characteristics of the follicular dynamics similar to those observed in other Zebu breeds, like the trend to a higher number of follicular waves associated with lower growth rate, maximum diameter and persistence of the dominant follicles emerging during non-ovulatory waves

Desenvolvimento folicular no pós-parto de vacas da raça Gir tratadas com acetato de buserelina (GnRH) ou gonadotrofina coriônica humana (hCG) Follicular development in Gir breed cows (Bos indicus) treated with buserelin acetate or human chorionic gonadotrophin during the postpartum period

Foram utilizadas 22 vacas da raça Gir (Bos indicus) em anestro pós-parto, amamentando e mantidas sob regime de pastejo. O padrão de crescimento folicular foi estudado em 15 animais, enquanto os outros sete foram utilizados somente no acompanhamento da resposta aos tratamentos hormonais. Ultra-sonografia em tempo real foi realizada diariamente, do quarto ao qüinquagésimo dia de lactação, por meio de aparelho equipado com probe de 5MHz. Nenhum animal apresentou estro, ovulação ou luteinização folicular durante o período de avaliação. Verificaram-se quatro a oito ondas foliculares surgindo em intervalos de seis a sete dias, cujo diâmetro máximo dos folículos dominantes e subordinados foi de 8,9±0,6 e 6,3±0,7mm, respectivamente. Aos 56 dias pós-parto, as 22 vacas foram divididas em dois grupos: 11 tratadas com 4,2 mig de acetato de buserelina e 11 com 3.000UI de hCG. A ovulação, regressão e luteinização folicular foram verificadas em animais dos dois tratamentos e uma nova onda folicular surgiu dentro de dois a três dias após a terapia hormonal. Corpos lúteos de menor tamanho e concentrações de progesterona abaixo de 1ng/mL indicaram baixa atividade luteal.<br>This experiment was carried out with 22 anestrus Gir cows (Bos indicus), with the postpartum follicular growth studied in 15 of these suckling and kept on pasture, while the seven others were used only for hormonal treatments. Daily real time ultrasonography was done from 4th to the 50th day, using B-mode ultrasound scanner equipped with a linear array 5.0MHz probe. No animal showed estrus, ovulation or follicular luteinization during de experimental period. Four to eight follicular waves emerged each six or seven days and maximum diameter of dominant and subordinate follicles were 8.9±0.6mm and 6.3±0.7mm, respectively. On day 56 of postpartum all cows were separated in two groups: 11 cows were treated either with 4.2 mug of buserelin acetate and 11 with 3,000UI of hCG. Ovulation, follicular regression and luteinization were observed in the two treatments animals, and one new follicular wave emerged within two to three days after the hormonal treatments. Small size corpus luteum and progesterone concentrations under 1ng/mL showed lower luteal activity