Udomprasert, Preeyaphan, Kitcha Urairong, Tawatchai Sakpuaram, and Worawidh Wajjwalku. 1999. “Influence of the Wean-to-first-service Interval on the Subsequent Farrowing Rate and Litter Size of Sows in Thailand”. Agriculture and Natural Resources 33 (1). Bangkok, Thailand:33-42. https://li01.tci-thaijo.org/index.php/anres/article/view/240427.