MATHUR, A K, et al. “Effect of Vitamin A and Mineral Administration on the Induction of Oestrus in Anoestrus Frieswal and Sahiwal Heifers”. The Indian Journal of Animal Reproduction, vol. 26, no. 1, June 2005, pp. 60-61, https://acspublisher.com/journals/index.php/ijar/article/view/6393.