Biological and economic consequences of introgression of the 'FecB' (Booroola) gene into Deccani sheep

Deccani sheep are reared on the Deccan plateau by smallholders under a system of supervised grazing on fallow and harvested fields and public lands. Lamb production is the main source of income. Deccani ewes usually give birth to only one lamb. The Nimbkar Agricultural Research Institute (NARI) introduced the 'FecB' mutation, which increases prolificacy, into the Deccani breed from the Garole breed of West Bengal to increase lamb production and incomes of smallholder shepherds. Two fecund strains were developed - the NARI Suwarna, with contributions from only Garole and Deccani breeds, and the Nari composite, with additional contributions from awassi and/or Bannur breeds. One copy of 'FecB' led to an increase in ovulation rate from 1.0 to 2.0 eggs, and an increase in live litter size (LS) at birth from 1.0 to 1.6 in the NARI flock and from 1.0 to 1.4 in smallholder flocks. Less than 5% of the litters of B+ ewes were triplets. The increased LS was found to be manageable under the existing production system of smallholders by keeping young lambs behind in the pens when ewes went grazing, and by providing lambs with a small amount of supplementary feed. The LS at 3 months of B+ ewes was 1.3 and 1.2 in NARI and smallholder flocks, respectively, compared to 0.9 of ++ ewes. In a smallholder flock with 8, 41 and 50 B+ ewes in 2005 to 2008, respectively, the gross margin per B+ ewe over the 3-year period was found to be 37-50% higher than the gross margin per ++ ewe. It is likely that the significantly larger LS of B+ ewes in the NARI flock, compared to B+ ewes in smallholder flocks, was due to the 100 g/day supplementary feed given to all ewes at NARI for 2 months at breeding and to the better body condition of ewes owing to longer lambing intervals. It could be termed a 'FecB' genotype by environmental interaction because the supplementary feeding did not influence the LS of non-carrier ewes. In conclusion, the introduction of the 'FecB' mutation in Deccani sheep proved to be successful in increasing both lamb production and incomes.