Small Ruminant Research zyxwvutsrq ELSEVIER Small Ruminant Research 23 ( 1996) 43-50 Effects on fertility and litter traits under accelerated lambing scheme in crossbreeding between Finnsheep and an Alpine sheep breed G. Bittante *, L. Gallo, P. Carnier, M. Cassandro, R. Mantovani, E. Pastore zyxwvutsrqpo Department of Animal Science, University of Pa&a, Agripolis, Via Romea, 3.5020 Legnaro (PD), Italy Accepted 5 October 1995 Abstract Analyses were conducted on data from 217 litters produced by mating Finnsheep (F) and Lamon (L) rams, a local Alpine Italian breed, to F, L, F X L and L X F ewes, with the aim of estimating breed direct, breed maternal, individual heterosis and maternal heterosis effects on litter traits and ewe productivity. Most differences between F and L were for maternal genetic effects, whereas differences in additive genetic effect were not significant for most traits. Finnsheep maternal effect improved pregnancy rate, particularly at synchronized estrus (+46%, P < 0.05) and litter size both per ewe lambing (+0.86, P < 0.05, and +0.60 at birth and at weaning respectively) and per ewe mated (+ 1.04, P < 0.05, and +0.67, P < 0.10, at birth and at weaning, respectively). Even though F maternal effect decreased average lamb weight at birth (- 2.5 kg, P < 0.01) and at weaning (- 1.6 kg), higher prolificacy of F derived ewes induced heavier litter per ewe mated ( + 6.7 kg, P < 0.10). Nearly all heterosis estimates were positive and relevant. Individual heterosis affected pregnancy rate, particularly at synchronized estrus (+ 17%, P < 0.05). and litter viability (+ 12%, P < 0.10). Individual and maternal heterosis improved litter size at birth and at weaning, especially on a per ewe mated basis (respectively +0.30, P < 0.10 and + 0.28 for litter size at weaning), and their effects on litter weight at weaning per ewe mated were substantial (respectively + 4.4 kg, P < 0.05, and + 2.3 kg). In conclusion the highest improvement of saleable lambs from crossbreeding of Italian Alpine meat sheep with Finnsheep can be obtained by the adoption of mating schemes which allow to exploit the genetic potential of Finn as maternal line and heterosis effect on lambs (individual heterosis) and on ewes (maternal heterosis). Keywords: Sheep; Crossbreeding; Finnsheep; Litter traits; Ewe production 1. Introduction A primary tool to improve the efficiency of meat production in sheep is the increase of the number of lambs marketed per ewe and per year (Dickerson, l Corresponding author. Tel.: (+39) 49 8272663; fax: (+ 39) 49 8272669; e-mail AGRAl lT@IPDLJNIVX.UNIPD.IT. 1970). As selection to enhance reproductive traits in sheep is rather slow (Bradford, 1985), crossbreeding of local with highly prolific breeds is widespread in many countries, with the aim of increasing lamb production combining breed attributes and exploiting heterosis. Finnsheep is one of the most prolific breeds and its history, development, use and productivity have been widely reviewed by Maijala and esterberg (19771, and by Maijala (1988). 00921~4488/96/$15.00 Published by Elsevier Science B.V. SSDI 0921-4488(95)008 12-8