ABSTRACT
En un par de líneas de ratones seleccionadas para alto (s') y bajo peso (s), originadas a partir de una población no seleccionada de la cepa CF1 (t), se modificó la estructura ovárica. El diámetro de los folículos ováricos y el número de folículos y de cuerpos lúteos se incrementaron en las hembras de la línea s', sin expresarse en un mayor tamaño de camada al nacimiento, posiblemente, por un aumento de las pérdidas gestacionales. Se probó si los efectos conjuntos de la selección de peso a largo plazo y de la estimulación ovárica incrementaban las pérdidas gestacionales. Se utilizaron dos grupos de hembras por línea: sin y con estimulación ovárica (5UI de eCG y 5UI de hCG). Las hembras se sacrificaron a las 56-72 hs y a los 7 días postservicio y después de la primera parición. Se observaron los números de cuerpos lúteos (CL), embriones (E) y sitios de implantación (SI) y el tamaño de camada al nacimiento (TC). Se estimaron las pérdidas totales (PT) y las pérdidas de cuerpos lúteos (PCL), de embriones (PE) y de fetos (PF). Los promedios de CL, E, SI y TC variaron en el mismo sentido de la selección practicada y fueron significativamente mayores (P<0,05) para las hembras estimuladas, a excepción de TC. La línea s' tuvo un potencial reproductivo superior pero un mayor costo biológico (mayor PT y más tardía) cuando se la comparó con las otras líneas. La estimulación ovárica produjo menores eficiencias reproductivas totales para las tres líneas y pérdidas gestacionales mayores y más tardías, principalmente de SI. Las hembras de la línea no seleccionada (t), no estimuladas, con pesos intermedios, parieron un mayor número de crías, partiendo de un número intermedio de CL, E y SI, con una menor y más temprana mortalidad embrionaria, demostrando ser las más eficientes desde el punto de vista reproductivo y productivo.
The ovarian structure was modified as a consequence of weight selection in a pair of mouse lines selected for high (s') and low weight (s). Lines were founded from an unselected population of CF1 strain (t). The follicle diameter and the number of the ovarian follicles and the corpora lutea were higher in s' females, but they did not reach a larger litter size at birth, may be, by an increase in the gestational losses. In these lines, the co-effects of long-term weight selection and ovarian stimulation were tested to evaluate if they increased gestational losses. Two groups of females per line were employed: without and with ovarian stimulation (5UI of eCG and 5UI of hCG). Females were slaughtered at 56-72hs and at 7 days post-breeding and after first parturition. The number of corpora lutea (CL), embryos (E) and implantation sites (SI), and litter size at birth (TC) were observed. Total losses (PT) and corpora lutea (PCL), embryo (PE) and fetus (PF) losses were estimated. Mean CL, E, SI and TC varied in the same direction of the selection made and they were significantly higher (P<0.05) in stimulated females, though not for TC. Line s' had a higher reproductive potential but a greater biological cost (higher and later gestational mortality) when compared with the other lines. Ovarian stimulation produced lower total reproductive efficiencies for the three lines and higher and later gestational losses, mainly for implantation sites. Females from unselected line (t), without ovarian stimulation, with intermediate weights, bore larger litters, starting from an intermediate number of CL, E and SI, with a lower and earlier embryo mortality, showing to be the most efficient from a reproductive and productive point of view.
Subject(s)
Animals , Female , Infant , Rats , Corpus Luteum/anatomy & histology , Corpus Luteum/embryology , Corpus Luteum/ultrastructure , Ovulation Induction/adverse effects , Ovulation Induction/methods , Embryo Loss/diagnosis , Embryo Loss/chemically induced , Embryo Loss/mortality , Reproductive Techniques/adverse effects , Reproductive Techniques/veterinaryABSTRACT
Avaliaram-se estratégias para reduzir a mortalidade embrionária em bovinos. Vacas Nelore (Bos taurus indicus) foram inseminadas em tempo fixo (IATF - D0) após o protocolo GnRH/PGF2a/GnRH e divididas nos grupos: Controle (Gc; n=55), hCG (GhCG; n=55) recebeu 3000 UI da hCG no D5 , E2 (GE2; n=55) recebeu 5 mg de 17?-Estradiol (E2) no D12 e hCG/E2 (GhCG/E2; n=55) recebeu 3000 UI da hCG no D5 e 5mg do E2 no D12. A IATF foi o 1o dia da estação de reprodução de 64 dias. Usou-se o teste do c2 para comparar as taxas de serviço (TS), concepção (TC) e prenhez à IATF (TPIATF), às IAs de repasse e acumuladas. A TS e a TC das IAs de repasse não diferiu (P>0,10). Houve diferenças nas TPIATF (P<0,05), pois a TPIATF do GE2 (5,4%) foi a mais baixa e a do Gc (34,5%) e GhCG (36,5%) tenderam (P<0,10) ser maiores que a do GhCG/E2 (18,2%). Não houve efeito da hCG sobre as taxas de prenhez. O E2 reduziu a TPIATF e ao final da estação as vacas que receberam o E2 (GE2 + GhCG/E2) tiveram TPacum (66,4%) mais baixa (P<0,05) de que aquelas (80,9%) que não receberam (GC + GhCG). Em conclusão, as estratégias adotadas de manipulação luteínica ou folicular não aumentaram as taxas de prenhez em vacas Nelore após uma IATF.
Strategies to reduce embryo mortality in cattle have been evaluated. Nelore (Bos taurus indicus) cows were submitted to timed artificial insemination (TAI - D0) after a GnRH/PGF2a/GnRH protocol. Cows were divided in the following groups: Control (Gc; n=55), hCG (GhCG; n=55) received 3000 IU of hCG on D5 , E2 (GE2; n=55) received 5 mg of Estradiol-17b (E2) on D12 and hCG/E2 (GhCG/E2; n=55) received hCG on D5 and E2 on D12. TAI represented the 1st day of a 64 day breeding season. The c2 test was applied to compare mating rate (MR), conception rate (CR) and pregnancy rate (PR) to TAI and AIs after natural estrus within the season as well as their accumulated figures at the end of the season. MR and CR for AIs within season did not differ (P>.10). PR to TAI differed (P<.05) among groups. GE2 showed the lowest rate (5,4%). Gc (34.5%) and GhCG (36.5%) tended (P<.10) to be higher than GhCG/E2 (18.2%). There was no effect of hCG on pregnancy rates. E2 reduced PR to TAI and at the end of season which means that cows receiving E2 (GE2 + GhCG/E2) had lower (66.4%; P<.05) PR than cows not receiving E2 (GC + GhCG; 80.9%). In conlusion, the strategies to manipulate luteal and follicular function herein tested did not increase pregnancy rates in Nelore cows submitted to a TAI.