RESUMEN
Colostrum is the first product secreted by the mammary gland to transfer immunity to the newborn, especially through immunoglobulins (Ig) G. Melatonin is an immunomodulatory factor and there is evidence that it has a direct effect on IgG production. To evaluate the effects of melatonin treatment during pregnancy, litter size and offspring sex on colostrum quality, sixty pregnant Rasa Aragonesa ewes were divided into three groups: one group received a melatonin implant at the third month of pregnancy (3M, n = 13), another group at the fourth month (4M, n = 18) and the remaining ewes were not implanted (Control, C, n = 29). Immediately after lambing, a sample of colostrum was collected and IgG, crude protein and fat content analysed. Timing of melatonin implantation (p < .001), and offspring sex (p < .01) had a significant effect on IgG concentration. Colostrum of treated ewes had a higher mean (±SEM) IgG concentration than that of the control ewes (55.54 ± 3.09 and 49.50 ± 4.36 mg/ml, respectively; p < .05), mainly because the concentration in the 4M group was significantly (p < .001) higher than it was in the other groups. The relationship between lamb sex and IgG (p < .01) and %CP (p < .05) was evident in singletons (ewes with a male lamb: 54.57 ± 5.37 mg IgG/ml, 15.42 ± 0.82%CP; ewes with a female lamb: 34.66 ± 4.30 mg/ml, 13.18 ± 0.73%CP). The presence of a female in the litter was associated with significantly (p < .01) lower colostrum IgG levels (litters with at least one female: 49.33 ± 3.42 mg/ml; litters with no females: 58.24 ± 4.00 mg/ml). Among 4M ewes, female foetuses had significantly (p < .01) lower IgG levels whether they carried singletons or multiple lambs. In conclusion, treatment with melatonin implants at the fourth month of pregnancy resulted in a higher colostrum quality based on IgG concentration.
Asunto(s)
Calostro/química , Melatonina/farmacología , Ovinos/fisiología , Animales , Animales Recién Nacidos , Implantes de Medicamentos , Femenino , Feto , Tamaño de la Camada , Masculino , Melatonina/administración & dosificación , EmbarazoRESUMEN
The effect of exogenous melatonin on prostaglandin secretion was measured on Rasa Aragonesa ewes. Fourteen ewes received an 18 mg melatonin implant (M+) on 10 April and were compared with 13 control animals (without implants M-). Twenty days later, intravaginal pessaries were inserted in all animals to induce a synchronized oestrus (day 0). On day 14, ewes were injected, i.v., with 0.5 IU oxytocin. Plasma 15-ketodihydro-PGF(2alpha) (PGFM) concentrations were measured to assess uterine secretory responsiveness to oxytocin. After euthanasia, pieces of endometrium were collected to determine progesterone content and PGE(2) and PGF(2alpha) secretion in vitro, in the presence or absence of either 20 microg/ml recombinant ovine interferon-tau (roIFNt) or 1 nmol/l oxytocin in the medium. Endometrial progesterone content was similar in the two treatments (M+: 50.25+/-17.34 ng/mg tissue, M-: 43.08+/-11.21 ng/mg tissue). M+ ewes that responded to oxytocin had significantly higher plasma PGFM concentrations between 10 and 80 min after oxytocin administration, a higher mean PGFM peak (P<0.001), higher plasma PGFM levels after the challenge (P<0.05) and higher plasma progesterone concentrations (P<0.01) than control ewes. In the in vitro experiment, M+ and M- control samples secreted similar amounts of PGE(2). The presence of roIFNtau and oxytocin only stimulated PGE(2) production (P<0.05) in M- tissues. Control M+ tissues secreted higher amounts of PGF(2alpha) (P=0.07) and PGF(2alpha) secretion was significantly (P<0.01) stimulated by roIFNtau. Oxytocin produced this effect only in M- samples (P<0.01). In conclusion, although previous studies have demonstrated a positive effect of melatonin on lamb production, PGF(2alpha) secretion is higher in vitro and the PGE(2):PGF(2alpha) ratio is unfavourable in response to IFNtau, which could affect embryo survival. Whether or not these mechanisms are similar in pregnant ewes remains to be elucidated.