تاثير وزن زنده و نمره وضعيت بدن ميش در زمان آميزش بر بازده توليد مثل و فصل بره زايي توده گوسفند كردي غرب كشور در شرايط پرورش سنتي

Effects of ewe live weight and body condition at mating on fertility and lambing season of Kurdy sheep in extensive production system

Ewe live weight and body condition score (BCS) were recorded in June, July and August over a period of 2 years (1999 and 2000) in five flocks of Kurdy sheep (1228 records from 614 breeding ewes) in pastorally based grazing (extensive) system in Ilam province (the western region of Iran). Dates of lambing (3100 records from 1570 breeding ewes during years 1994 to 2000) and mating (1228 records from 614 breeding ewes) were also investigated. The peaks of mating and lambing were in July and December, respectively. Ewes were classified according to fertility and lambing season as Autumn-lambed, Winter-lambed and barren. Ewe live weights measured in June, July and August had significant influences on the fertility and lambing season (p< 0.01). Ewes which produced lambs were generally heavier at mating than barren ewes (p< 0.05). Autumn-lambed ewes were heavier than winter-lambed ewes in June and July (p< 0.05) . The difference between least squares means for August live weight of Autumn-lambed and Winter-lambed ewes was not significant. Effects of changes in live weight on the fertility and lambing season were significant (p< 0.05). Fertility and lambing season were significantly affected by ewe age (p< 0.01). The proportion of barren ewes decreased significantly with age from 17 % to 9% for 2 to 5 years gradally (p< 0.05). The effects of ewe body condition score (BCS) in June, July and August (p<0.01) and changes in BCS during mating period (p< 0.05) on fertility and lambing season were significant. The least squares mean of BCS (in June and July) for Autumn-lambed ewes was greater than winter-lambed and barren ewes (p< 0.05). The difference between least squares means for August BCS of autumn-lambed and winter- lambed ewes was not significant. The least squares mean of BCS (in June and July) for barren ewes was lower than those which produced lambs (p<0.05). The proportion of autumn-lambed ewes increased significantly (p< 0.01) with BCS (in July) from 2.0 to 3.5 units, while the proportion of barren ewes decreased (p< 0.05) over the same BCS range accordingly. The results demonstrate the importance of flushing to younger ewes and ewes with low BCS (in late Spring and early Summer) in order to reduce proportion of barrens and increase proportion of Autumn-lambed ewes.