Resumo: This trial aimed to test eCG as an enhancer of the luteal function, as well as to evaluate the ability of eCG to delay or prevent luteolysis mechanism. A group of 32 mature, synchronized (CRESTAR@), lactating Nelore (Bos taurus indicus) cows were randomly allotted to receive either 400 lU of eCG at implant withdrawal (GeCG; n=16) or remain as contrais (GC; n=16). Ultrasound per rectum evaluation of avaries was conducted daily, from implant rem oval up to the following ovulation (a complete estrous cycle). Simultaneously, blood samples were taken to determine plasmatic concentration of progesterone ([P4]). Data were analyzed by GLM of the SAS program. GeCG showed non-significant (P>.05) higher volume of corpus luteum (CL) from day 3 after synchronized ovulation up to lhe rest of lhe luteal phase. In addition, eCG promoted a longer lasting growing period of lhe CL without changing its growing rale (P>.05) as compared to GC. As a result, CI maximum volume was reached later (9.2:t .47 days) and achieved a larger dimension (6927.5:t 405.86 mm3) for GeCG than occurred for GC (respectively, 7.7:t .47 days and 5437.8:t 405.86 mm3). The peak of [P4] was observed at lhe same time for both groups (11.3 t .59 and 11.4 t .59 days for GeCG and GC, respectively). However, maximum [P4] was higher (P<.O5) for GeCG (8.2 t .64 ng/mL) than Gc (6.4 t .64 ng/mL). Luteolysis also took place at lhe same time (P>.O5) for both groups (17.3 t .45 to GeCG and 17.1 t .45 days of lhe estrous cycle to GC). As a consequence, estrous cycle length did not differ (P>.O5) between treated (21.8 t .57 days) and non-treated cows (21.4 t .57 days). In summary, eCG not only increased CL dimension but also optimized [P4] over the luteal phase ofthe estrous cycle. Therefore, eCG given at implant removal provided a luteotrophic effect, but it was not capable to delay luteolysis.

Ano de publicação: 2006

Tipo de publicação: Resumo em anais e proceedings

Unidade: Embrapa Pecuária Sudeste