Espinel Barajas, Katherin Yulieth Espinel Barajas Yulieth, et al. “Comfrey As a Complement or Vitamin Substitute for the Production of Alternative Foods in Pigs”. Perspectivas, vol. 3, no. 10, Dec. 2018, pp. 138-44, https://revistas.uniminuto.edu/index.php/Pers/article/view/1778.