Oocyte pick-up in juvenile lambs affects neither onset of puberty nor their future fertility

Abstract

A study was designed to evaluate whether the time of onset of puberty and fertility of young ewe lambs would be affected by oocyte pick-up conducted in single or repeated sessions during the first months of lambs' live. Five groups of lambs from the Karagouniko breed were used (A-E each n = 12). In group A no treatments were applied (control group) while, laparoscopical follicular aspiration (OPU) was performed early in the third, fourth and fifth month of lambs age (groups C-E, respectively). From the second to fifth month of their age, group B lambs were aspirated four times in monthly intervals. All lambs were weighed at birth, weaning, at second month and monthly thereafter until the eighth month of age. Progesterone priming and ovarian stimulation by serial FSH administrations proceeded each OPU session. To determine onset of puberty blood progesterone concentration was assayed in samples collected initially every week and after the seventh month of age twice weekly. From the seventh month a fertile ram was introduced in each group and oestrous behavior/mating was daily monitored and recorded. Pregnancy diagnosis was carried out by transabdominal ultrasound scanning 55 days after rams' removal. At the fourth and fifth month of age group B lambs were lighter (p < 0.05) than controls, but this difference was later equalized. The time of onset of puberty did not differ between groups (p = 0.069) and ranged between 224 and 270 days. Some animals (n = 15) entered puberty with a full-length luteal phase having progesterone concentration greater than 1 ng/ml, while others (n = 32) exhibited one or two short luteal phases before luteal length restoration. During the first breeding season 41 animals were fertilized and maintained pregnancy to term, without noticeable differences between groups (p = 0.555). During the second breeding season, all ewes were naturally served and lambed at the expected time. It is concluded that OPU in young dairy lambs does not affect the time of onset of puberty, the endocrine profile of the lambs and it does not compromise their future fertility even if it is applied at four successive months. © 2006 Elsevier Inc. All rights reserved.