Gerhart, K. L., R. G. White, R. D. Cameron, D. E. Russell, and D. van de Wetering. “Pregnancy rate as an indicator of nutritional status in Rangifer. implications of lactational infertility”. Rangifer, vol. 17, no. 1, Apr. 1997, pp. 21-24, doi:10.7557/2.17.1.381.