Oxeye Daisy
      I've found nothing about this plant in any of my toxin books. As part of the Asteraceae family it likely contains sesquiterpene lactones. I have found numerous references to sheep, goats, horses and cattle eating it. I've also found notes that the flavor of milk may change when dairy animals eat this plant.
      Ox-eye daisy spreads through abundant seed production and vegetatively by rooting underground stems (rhizomes) (Griswold 1985). Georgia (1914 found that seeds can bcome viable 10 days after the flower opens, and according to Salisbury (1942) an oxeye daisy plant may produce over 2,500 offspring per year. The plant can also resprout if the roots and rhizomes are not completely removed. Seeds can also remain viable for long periods of time. In a rial conducted by Toole and Brown (1946), 82% of the seeds were still viable after 6 years and 1% of the seeds were viable after 39 years.
     The effects of intensive cattle grazing on oxeye daisy were assessed in southwestern Montana by B.E. Olson and R.T. Wallander. They found that two years of intensive grazing reduced densities of oxeye seedlings and rosettes. Though the study showed no effect on densities of adult plants compared with densities in adjacent, ungrazed exclosures during the two year period of the study, they believed that by reducing densities of the seedlings and rosettes, densities of adult plants would have decreased in subsequent years had the study been able to continue. They also found that the intensive grazing had minimal impact on perennial grasses in the pastures. Further, they found that overall use on the daisy was similar to use on the other vegetation, so there was no strong avoidance to the plant.
    It's important to note that biting off the flowers promotes the rapid development of many lateral stems. In addition, Howarth and Williams found that of the seeds passing through the cow somewhat less than 40% are still viable. Considering that each flower can produce 1,300 to 4,000 seeds (Dorph-Petersen 1925), a 40% seed survival rate means you should be careful how you manage your animals if your goal is not to spread the plant to unaffected areas.

References - Drawn from "The Identification, Distribution, Impacts, Biology and Management of Noxious Rangeland Weeds," Roger Sheley, an October 14, 1994 report for the Interior Columbia Basin Ecosystem Management Project Scence Integration Team Terrestrial Staff Range Task Group

Dorph-Petersen, K. 1925. Examinations of the occurrence and vitality of various weed seed species under different
conditions, made at the Danish State Seed Testing Station during the years 1896-1923. Rep. 4th Int. Seed Test. Congr.
4:128-138.

Howarth, S.E., and J.T. Williams. 1968. Biological flora of the British Isles. J. Ecol. 56:585-595.

Georgia, A. 1914. A manual of weeds. MacMillan, NY. 593 p.

Salisbury, E.J. 1942. The Reproductive Capacity of Plants. G. Bell and Sons Ltd, London.

Toole, E.H., and E. Brown. 1946. Final results of the Duvel buried seed experiment. J. Agri. Res. 72:201-210.