The annual report for the Shackleford herd in 2020 says “Contraception has been linked to increased longevity among treated females.”
One explanation, not invented here, is that treated mares don’t have to go through the stress of pregnancy, birth and caring for a new foal.
Stallions don’t go through any of that, yet they only represent about one third of the Shackleford population.
On the Maryland side of Assateague Island, females outnumber males 2.4 to 1.
Both herds are subject to ‘humane management practices.’
A difference is that the disparity at Shackleford can be attributed to chance, random noise in the process, while the imbalance at Assateague is so large that it must be attributed to an assignable cause, a signal of trouble in the herd.
That may explain why the fertility control program was shut off in 2016.
Are the Shackleford horses heading in the same direction? Do contraceptives have other effects that would limit their use? Is the cup half full or half empty?
RELATED: Shackleford Herd Grows In Latest Census.