Oestrogenic effects of lucerne in female sheep

Abstract

Leguminous fodder crops such as lucerne contain oestrogenic substances and their precursors that may interfere with reproduction in sheep. There is no definite information about the actual levels of oestrogenicity of New Zealand lucerne crops and the magnitude of the effect that they have on the reproduction of sheep. There is no information about when a crop may be unsafe for ewes to graze just prior to mating and a simple measurement of sheep is needed to provide an alert so sheep farmers can move sheep off a crop or leave them on knowing that there will be no deleterious effects on subsequent lambing performance. The sheep farm study was an incidental finding from a farmer who noticed udder development in pre-pubertal (25 - 28 weeks of age) lambs (n = 22) grazing lucerne (oestrogenicity ranging from 98.6 – 149.6 µg oestradiol equivalent/kg DM) compared with lambs grazing grass (n = 36) that showed no udder development. Differences in teat length, teat width, mammary development and vulva colour were measured on two occasions – straight after grazing oestrogenic lucerne (12 March) and 35 days later (16 April), 4 weeks after the removal from the lucerne crop. The experimental study was designed to provide a reference calibration with known dosage of an oestrogen. For this 12 Coopworth ewes (42 - 44 weeks of age) were randomly assigned to one of three treatments (n = 4, per treatment): 0, 0,1, 1.0 mg β-oestradiol every 3 days for 40 days. Measurements of teat length, teat width and mammary development was measured every 6 days and, on day 41, the ewes were killed and vulva colour, mammary weight, ovary weight and uterus weight were measured and the number of follicles and corpora lutea were counted. In both studies photographs of the mammary region were taken to provide an alternative measurement technique to use of calipers. Results of the sheep farm study showed lambs grazing oestrogenic lucerne were heavier, had longer teat lengths (2.1 mm difference), with larger teat widths (4.63 mm difference) than sheep grazing grass and mammary development (in 14 out of 25 lambs grazing lucerne) had occurred. There was no change in vulva colour. After removal from lucerne there was a slight reduction in the oestrogen-related changes and the grass-fed lambs had experienced some mammary/teat development in the intervening period. In the experimental trial, there were dose-related effects on the live weight, teat length, mammary development, uterus weight, ovary weight and mammary weight. There were no changes in teat width, vulva redness or colour saturation, numbers of ovarian follicles and there were no corpora lutea present. Measurements taken from photographs provided reliable information about mammary/teat dimensions. Although the pre-pubertal lambs grazing lucerne were receiving less oestradiol equivalent daily than the older ewes supplied with known amounts of oestradiol (181.2 – 274.9 µg oestradiol equivalent versus 333.3 µg oestradiol per day, respectively), they showed a greater sensitivity to this hormonal stimulus than was exhibited by the pubertal ewes.