Desenvolvimento ponderal e testicular, concentrações periféricas de testosterona e características de abate em touros da raça Nelore

Abstract

RESUMO -Um experimento foi conduzido com o objetivo de avaliar o desenvolvimento ponderal e testicular, as concentrações periféricas de testosterona (T) e características de abate, dos 10 aos 30 meses de idade, em tourinhos da raça Nelore (n=27). Entre 11 e 21 meses, os animais foram tratados com GnRH e amostras de sangue, coletadas 0, 1,5 e 3,0 horas depois. Aos 30 meses, os animais foram abatidos. O peso vivo (PV) dos animais variou de 195,2 ± 3,8 kg a 439,1 ± 8,1 kg entre 10 e 30 meses e o rendimento de carcaça foi de 55,4 ± 2,3%. Os pesos dos testículos (PT) e do epidídimo (PE) aos 30 meses foram 160,9 ± 7,7 g e 20,4 ± 0,62 g, respectivamente.As concentrações de T apresentaram crescimento maior entre 16 e 18 meses e o tratamento com GnRH ocasionou aumentos nos níveis de T em todas as idades. As concentrações de testosterona estimuladas com GnRH estiveram associadas às concentrações basais (r = 0,41 a 0,63). Houve correlações entre PV e circunferência escrotal (CE) em todas as idades (r = 0,41 a 0,70). O peso corporal entre 10 e 30 meses apresentou correlações com PT (r = 0,48 a 0,62) e PE (r = 0,48 a 0,73) aos 30 meses e animais com maior peso de carcaça também tiveram maiores pesos testicular (r = 0,45) e epididimal (r = 0,63). Houve correlações entre PV (10 e 30 meses) e peso da carcaça (r = 0,65 a 0,93), mas o rendimento de carcaça não apresentou relação com CE, PT, PV ou níveis de testosterona. Foram significativas também as correlações entre a CE aos 30 meses e a CE avaliada entre 10 e 25 meses (r = 0,51 a 0,89). Portanto, medidas testiculares são potenciais indicadores do desenvolvimento ponderal e das características de abate na fase adulta.Palavras-chave: carcaça, circunferência escrotal, GnRH, Nelore, testosterona Testicular and Body Growth, Peripheral Concentrations of Testosterone and Carcass Parameters in Nelore BullsABSTRACT -An experiment was carried out to evaluate testicular and body growth, peripheral concentrations of testosterone (T) and carcass parameters, from 10 to 30 months of age, in Nelore bulls (n=27). Between 11 and 21 months, animals were treated with GnRH and blood samples taken 0, 1.5 and 3.0 hours afterwards. Animals were slaughtered at 30 months. Body weight (BW) varied from 195.2 ± 3.8 kg to 439.1 ± 8.1 kg between 10 and 30 months of age and the ratio BW/carcasss was 55.4 ± 2.3%. Testicular (TW) and epididimal weight (EW) at slaughter were 160.9 ± 7.7 g and 20.5 ± 0.62 g, respectively. Testosterone secretion reached higher levels between 16 and 18 months and treatment with GnRH caused increases in testosterone at all ages. Moreover, basal concentrations of T were related to those determined after GnRH (r = 0.41 to 0.63). Body weight from 10 to 30 months was correlated with SC at all ages (r = 0.41 to 0.70) and with testicular (r = 0.48 to 0.62) and epididymal weight (r = 0.48 to 0.73) at 30 months. Carcass weight was related to TW (r = 0.45) and EW (r = 0.63). Body weight evaluated from 10 to 30 months was related to carcass weight (r = 0.65 to 0.93), but the ratio BW/carcass...

Testis size, peripheral concentrations of testosterone, semen criteria and Sertoli and germ cell numbers in Nelore bulls

“…According to studies conducted in the Bos taurus and Bos indicus, puberty coincides with the typical peak in basal concentrations of testosterone in the peripheral circulation (AMANN, 1983;ARAVINDAKSHAN et al, 2000;GHOLAMI et al, 2010;ERICKSON, 2011). For the Nelore bulls used in the present study, the characteristic peak in basal testosterone occurred at 18 mo., suggesting these animals reached puberty at that age, as we have originally pointed out (MOURA; RODRIGUES; MARTINS FILHO, 2002). Previous reports have shown that Nelore bulls attain puberty at ages from 14.8 to 22.1 mo.…”

“…Results about age-related changes in scrotal circumference and basal and GnRH-stimulated testosterone have been previously described in detail (MOURA; RODRIGUES; MARTINS FILHO, 2002). In summary, scrotal circumference of the Nelore bulls increased between 10 and 30 mo.…”

“…However, we cannot assume that Bos indicus bulls have either higher or lower rates of cell loss than Bos taurus bulls because the animals used in the studies cited above had different ages and weights as well as were raised and fed in very different conditions when compared to ours. Cell loss that occurs during spermatogenesis, due to apoptosis, has been reported in several species and it is caused by altered gene expression during mitosis and meiosis and/or external factors such as heat stress, chemical agents and nutritional imbalance (PRINT; LOVELAND, 2000;SOFIKITIS et al, 2008;CHENG et al, 2010). For the Nelore bulls, the average nucleus and nucleolus diameters of Sertoli cells were 8.4 ± 0.4 and 3.5 ± 0.2 μm, and those of spermatogonium reached 7.6 ± 0.5 and 3.3 ± 0.2 μm, respectively.…”

“…As previously described in the first publication about this study (MOURA; RODRIGUES; MARTINS FILHO, 2002), scrotal circumference (SC) and both testis diameter and length were recorded at monthly intervals, from 10 to 29 months (mo.) of age.…”

“…Immediately after collection, samples were centrifuged at 1,500 × g for 20 minutes at 4 ºC. Plasma was harvested and stored at -20ºC until determination of testosterone concentrations by radioimmunoassay (Diagnostic Products Corporation, USA; MOURA; RODRIGUES; MARTINS FILHO, 2002;SOUZA et al, 2010). The dose of GnRH per kg of body weight and the approach of blood sampling were based on our previous studies conducted in prepubertal, pubertal and post pubertal beef bulls (MOURA; ERICKSON, 1997;2001).…”