Fatima Souza

ABSTRACT This study aimed to evaluate the efficiency of recombinant bovine somatotropin (rbST) on pregnancy rate (PR), dominant follicle diameter (DFD) pre-ovulatory follicle diameter (DFPO), and follicular growth rate (FGR) in Bos indicus cows with low body condition score (BCS; mean = 2.3) subjected to fixed-time artificial insemination (FTAI) protocols. The females were divided into four groups: rbST group day zero (GbSTd0; n=31) received a progesterone (P4) intravaginal device + estradiol benzoate + rbST on d0 of the protocol; on d8, P4 was removed and PGF2???? + estradiol cypionate were administered; on d10, FTAI was performed; GbSTd8; n=31) received the same treatment as GbSTd0, except rbST administration on d8; the control group (GC; n=42) received the same treatment as GbSTd0 but without rbST; equine chorionic gonadotropin group (eCGG; n=46) received the same treatment as GC + eCG on d8. Ovarian follicles were evaluated by ultrasonography (US) on d0, d8, and d10 of the protocols. PRs (at d35) and FGR between d8 and d10 of the protocol were calculated. PRs resulted 16.1%, 19.4%, 30.9%, and 43.4% in GbSTd0, GbSTd8, GC, and GeCG, respectively. eCGG PR differed significantly (P<0.05) from rbST groups but not to the GC; no difference was observed between rbST groups and GC. eCGG resulted in larger DFPO (11.2±1.5 vs. 9.6±0.5 in GbSTd0; 9.9±0.8 in GbSTd8; 10.1±1.3 in GC; P=0.0001) and greater FGR (2.20±1.03 vs. 0.93±0.50 in GbSTd0; 0.94±0.52 in GbSTd8; 1.17±0.64 in GC) (P<0.0001). It was concluded that rbST groups resulted in lower PR, FGR, and DFPO compared to eCGG in cows with reduced BCS; therefore, eCG is recommended for use in cows with low BCS in FTAI programs. Keywords: recombinant bovine somatotropin, equine chorionic gonadotropin, Bos indicus, follicular dynamics, FTAI RESUMO O estudo objetivou verificar a eficiência da somatotrofina recombinante bovina (rbST) sobre a taxa de prenhez (TP), o diâmetro do folículo dominante (DFD) e do pré-ovulatório (DFPO) e a taxa de crescimento folicular (TCF) de vacas Bos indicus com baixo escore corporal (ECC médio=2,3) submetidas a protocolos de inseminação artificial em tempo fixo (IATF). As fêmeas foram distribuídas em quatro grupos: grupo bST dia zero (GbSTd0; n=31) recebeu, no d0 do protocolo, um dispositivo intravaginal com progesterona (P4) + benzoato de estradiol + rbST; no d8, houve a remoção da P4 e foi aplicado PGF2???? + cipionato de estradiol; no d10, executou-se a IATF; GbSTd8 (n=31) recebeu idêntico tratamento ao GbSTd0, exceto a aplicação da rbST no d8; grupo controle (GC; n=42) recebeu o idêntico tratamento ao GbSTd0, exceto a não aplicação da rbST; grupo gonadotrofina coriônica equina (GeCG;n=46) recebeu idêntico tratamento ao GC + eCG no d8. Os folículos ovarianos foram avaliados por exames de ultrassonografia (US) em d0, d8 e d10 dos protocolos. Foram calculadas as TPs (no d35) e a TCF entre d8 e d10 do protocolo. As TPs resultaram respectivamente em 16,1%; 19,4%; 30,9% e 43,4% nos GbSTd0, GbSTd8, GC e GeCG. As TPs do GeCG mostraram diferença (P<0,05) em relação aos grupos da rbST, mas não ao GC; não houve diferença entre os grupos rbST e o GC. A eCG resultou em maior DFPO (11,2±1,5 vs. 9,6±0,5 do GbSTd0; 9,9±0,8 do GbSTd8 e 10,1±1,3 do GC; P=0,0001) e maior TCF (2,20±1,03 vs. 0,93±0,50 do GbSTd0; 0,94±0,52 do GbSTd8, 1,17±0,64 do GC) (P<0,0001). Concluiu-se que os grupos rbST resultaram em menor TP, TCF e DFPO que a eCG, em vacas com reduzido escore ECC; recomenda-se o emprego da eCG em vacas com baixo ECC em programas de IATF. Palavras-chave: somatotrofina recombinante bovina, gonadotrofina coriônica equina, Bos indicus, dinâmica folicular, IATF