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The and and semi-arid tropical climates of India are endowed with vast diversity of non-prolific sheep breeds. The Garole x Malpura sheep has been evolved in a semi-arid tropical environment by introgression of FecB gene via artificial insemination of Malpura ewes using diluted semen of prolific microsheep Garole and subsequently multiplied by inter se mating among Garole x Malpura halfbreds. The aim of the present study was to identify FecB mutation in sexually mature Garole x Malpura rams by forced RFLP-PCR of BMPR-1B gene and evaluate: (i) semen production and sperm motion characteristics of GM rams and (ii) influence of age and FecB genotype on their semen attributes. Semen was collected during autumn season from 12 donor rams by artificial vagina on 8 occasions at weekly interval. The overall means of traits which did not differed significantly with age or FecB genotyping were volume (0.72 ml), mass motility (4.44), sperm concentration (2721.56 x 106 ml(-1)), curvilinear velocity (134.51 mu m/s), motility (81.3%), amplitude of lateral head displacement (6.24 mu m), beat frequency (44.43 Hz), sperm head elongation (48.9%) and sperm head area (10.01 mu m(2)). The FecB genotyping had a significant effect (P < 0.05) on percent linearity and rapid motile sperms, which did not vary significantly with age. Although sperm concentration was higher in FeCBBB and FecB(B+), compared to FecB(++) genotypes but the effect was non-significant. The age and FecB genotyping had significant effects (P < 0.05) on straightness, average path velocity, straight-line velocity and percentage of medium or slow motile sperms. It is concluded that Garole x Malpura rams with introgressed FecB gene are capable of producing good quality semen in a semi-arid tropical climate. (C) 2006 Elsevier B.V. All rights reserved.