Premature mammary development in ewe lambs exposed to an oestrogenic lucerne pasture

A report of mammary development in 6-month-old ewe lambs grazing lucerne on a commercial farm in North Otago provided an opportunity to investigate the possibility to use this as a tool to detect oestrogenic lucerne pastures. Of the 36 ewe lambs grazing lucerne at this farm, protruding mammary glands were visible in 19. In contrast, none of the 22 ewe lambs grazing grass had protruding mammary glands. The lucerne-fed ewe lambs also had larger mean teat width than the grassfed ewe lambs (17.9 ± 0.53 mm versus 13.4 ± 0.78 mm respectively. The lucerne-fed animals were returned to grass pasture 4 weeks before the introduction of rams. There was no effect of the earlier 16 weeks of lucerne grazing on the number of fetuses present in ewes near mid-gestation compared with ewes on grass throughout this period. These findings from a commercial farm suggest that oestrogenic lucerne may be detected by monitoring ewe lambs for mammary development. This would enable farmers to manage pre-mating grazing of ewes with minimal risk of lowered ovulation rates.