“Extra-Caloric” Properties of Acidulated Soybean-Oil Soapstock for Broilers during Hot Weather

Three trials were conducted with a total of 690 broilers from 7–13 to 55 days of age; two trials in the summer and one in the winter (under natural climatic housing conditions). All trials involved the same four dietary treatments, with increasing levels (1% to 10%) of acidulated soybean soapstock (ASS), along with pulverized basalt stone, in isocaloric substitution for a glucose:starch mixture. In the two trials performed during the summer there was a graded response in growth rate to increasing dietary levels of ASS, both during the starting and finishing periods, due primarily to increasing feed consumption (with little effect on feed/gain ratios). The trial conducted during winter did not yield corresponding results, thus placing in doubt the involvement of palatability or unknown growth factors. It is assumed that the beneficial effect of ASS on growth rate during summer was due to the reduced heat increment of this fat supplement, which helped the broilers to withstand the appetite-depressing effect of heat stress.