DEKA, K C, et al. “A Comparative Appraisal of Serum Progesterone Level During Oestrous Cycle in Normal and Repeat Breeder Crossbred Cows With Ovulatory Problem”. The Indian Journal of Animal Reproduction, vol. 28, no. 2, Dec. 2007, pp. 83-85, https://acspublisher.com/journals/index.php/ijar/article/view/5074.