@misc{indiciae551cca2661eb,
  title = {Sharp increase in free circulating oestrogens immediately before parturition in sheep.},
  author = {J R Challis},
  year = {1971},
  doi = {10.1038/229208a0},
  url = {https://pubmed.ncbi.nlm.nih.gov/4923273/},
  note = {Source identifier: 4923273}
}