The productivity, ovarian and thyroid activity of ewes in an accelerated lambing system in Greece

The present study was conducted to compare the ewe’s productivity between two lambing seasons, as part of an accelerated lambing system of four lambings in 3 years. The evaluated two lambing seasons represent an out of season lambing season in summer (July) and a natural lambing season in spring (March). Fifteen crossbred ewes (Karagouniko×Mytilene) were used. Estrous synchronization was induced by the “ram effect” and the duration of the suckling period was kept the same for both lambing seasons (53.2±1 and 56.0±2 days). Prolificacy was 1.73±0.1 and 2.47±0.2 lambs born/ewe lambing (P < 0.001) for the summer and spring lambing seasons, respectively. The mean lamb birth and weaning weight (twins only) were 3.9±0.2 kg versus 3.4±0.2 kg (P < 0.05) and 19.1±0.6 kg versus 16.4±0.4 kg (P < 0.001), respectively, for spring and summer lambing seasons. The duration of the lactation period was significantly longer for the summer lambing (94.4±2 days versus 68.5±3 days, P < 0.001), resulting in a significantly higher milk yield (92.1±7 l versus 67.2±7 l, P < 0.05), respectively. According to serum progesterone levels, a significant difference was recorded for the number of ovarian cycles (progesterone levels >1.0 ng/ml for 2 subsequent weeks) for the period from weaning to mating (1.7±0.2 and 1.0±0.2 for the summer and spring lambing seasons, respectively; P < 0.05). Serum thyroxine levels in ewes were lower during the summer, compared to the spring suckling period (45.4±2 and 61.5±4 ng/ml, P < 0.001), respectively, and also during the interval from weaning to mating (48.4±2 and 64.5±4 ng/ml, P < 0.001) for the summer and spring lambing seasons, respectively. It could be concluded that summer and spring lambing seasons as a part of an accelerated lambing system of four lambings in 3 years could result in increased ewe productivity (in terms of prolificacy, lamb birth weight, and weaning weight) – being greater for the spring lambing season. Ovarian activity, as estimated by serum progesterone levels, reflects the stage of the breeding season of the ewes. Thyroid function showed the typical seasonal pattern, irrespective of the ewe’s productive stage. © 2005 Elsevier B.V. All rights reserved.