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Twin lambs from a FecB-carrier ewe Photo: placeholder pending image-fill pass

FecB (Booroola) prolificacy gene in Indian sheep

FecB, also known as the Booroola gene, is a single major-effect mutation in the bone morphogenetic protein receptor IB (BMPR-IB) gene that increases ovulation rate and litter size in sheep. The mutation, originally identified in the Australian Booroola Merino, is present in the Indian indigenous Garole sheep of West Bengal and has been used by ICAR-CSWRI Avikanagar to develop prolific synthetic strains.

Genetic background

The FecB mutation is a Q249R amino-acid substitution in BMPR-IB. The gene is autosomal with an additive effect on ovulation rate and a near-dominant effect on litter size. Ewes carrying one copy (FecBB/FecB+) ovulate roughly 1 extra egg and produce 0.8-1.0 extra lambs per lambing compared with non-carriers, while homozygous carriers (FecBB/FecBB) ovulate around 3 extra eggs but show diminishing returns in lambs born. The mutation is detected through PCR-RFLP testing.

Source breed in India

The Garole sheep (Garole Sheep Sundarbans) of the Sundarbans of West Bengal is the only Indian indigenous breed known to carry the FecB allele at high frequency, and is the recognised genetic source for FecB introgression into other Indian sheep. The Indian origin of the Booroola allele itself is supported by the historical export of Bengal sheep to Australia in the 18th century.

Use in synthetic strains

ICAR-CSWRI Avikanagar has used Garole crosses to introgress FecB into Malpura (Malpura Sheep Rajasthan Mutton) and Patanwadi sheep. The resulting synthetic strains — Garole x Malpura (GMM) and Garole x Marwari — show roughly doubled twinning rates compared with the indigenous dam breed, with lambs per ewe lambing rising from 1.05 to 1.6-1.7. The carriers are bred with structured culling to retain FecBB heterozygotes, since homozygotes can produce litter sizes too large for adequate maternal milk supply.

Management implications

Introducing FecB shifts lambing management decisively: ewes need supplementary feeding in late gestation and lactation, lambs often need cross-fostering or supplementary milk replacers, and lambing pens must accommodate twins and triplets. Without these inputs, the genetic gain in litter size is lost to lamb mortality. PPR (Ppr Vaccination Detailed) and structured small-ruminant vaccination (Small Ruminant Vaccination Schedule) remain unchanged.

See also: Garole sheep, Malpura sheep, Marwari sheep.

Sources

  1. FecB introgression in Indian sheep. ICAR-Central Sheep and Wool Research Institute, Avikanagar.
  2. Booroola FecB research. ICAR-National Bureau of Animal Genetic Resources.