Data/hora: 09/06/2024 06:37:18

Biblioteca(s): | Embrapa Caprinos e Ovinos.
Data corrente: | 31/10/2002
Data da última atualização: | 31/10/2002
Autoria: | ROSA, H. J. D.; JUNIPER, D. T.; BRYANT, M. J.
Título: | Effects of recent sexual experience and melatonin treatment of rams on plasma testosterone concentrations, sexual behaviour and ability to induce ovulation in seasonally anoestrous ewes.
Ano de publicação: | 2000
Fonte/Imprenta: | Journal of Reproduction and Fertility, v. 120, n. 1, p. 169-176, 2000.
Idioma: | Inglês
Conteúdo: | The aim of this study was to determine whether advancing the seasonal changes associated with rams by treatment with exogenous melatonin and a11owing the rams previous sexual experience would increase the proportion of anoestrous ewes ovulating in early July. North Country Mule ewes (n = 225) were grouped by live body weight and body condition score and a11ocated randomly to the following treatments: (i) isolated from rams (control; n = 25); (ii) introduced to rams (treatment 2); (iii) introduced to rams that had mated with ewes during the previous 2 days (treatment 3); (iv) introduced to rams implanted with melatonin (treatment4); and (v) introduced to rams that were implanted with melatonin and had mated with ewes during the  previous 2 days (treatment 5). Treatments 2-5 were replicated (2 x 25 ewes) and two rams were introduced to each replicate group. Introductions began on 4 July and were completed by 11 July. The rams were withdrawn from the ewes after 8 days. Melatonin was administered as a subcutaneous implant (Regulin®) on 22 May and again on 20 June. Blood samples were taken from all rams to determine plasma melatonin and j testosterone concentrations (19 samples in 6 h). The behaviour of the sheep was videotaped continuously during the first 3 h after the ram was introduced. Ovulation was detected by an increase in plasma progesterone concentrations from < 0.5 ng ml-l to > 0.5 ng ml-l. Mean +- SE plasma melatonin concentrations were 649.7 +- 281.4 and 18.3 +- 2.4 pg ml-l in rams with and without melatonin implants, respectively (P < 0.001). Melatonin implants also increased plasma testosterone concentrations from 4.30 +- 1.88 to 10.10 +- 1.10 ng ml-l (P < 0.01), the libido of the rams and the proportion of ewes that ovulated in response to the rams (43 and 56% (treatments 4 and 5) versus 24% (treatments 2 and 3). In conclusion, implanting rams with melatonin before introducing them to seasona11y anoestrous ewes increases the proportion of ewes that ovulate in response to introduction of a ram, but previous sexual experience of rams appears to have little or no effect.
Palavras-Chave: | Anestro; Efeito macho; Melatonina; Nível plasmático.
Thesagro: | Comportamento Sexual; Indução; Ovelha; Ovino; Testosterona.
Categoria do assunto: | --
Registro original: | Embrapa Caprinos e Ovinos (CNPC)
Exemplares: | CNPC - (15061-1) - ADC - AP - -- -  -  - v.120, n 1 - DIS