Abstract
The rise in the environmental temperature due to climate change alters the basic physiology of the ruminants; hence negatively affect ruminant production. Thus exposure to the hot environment is considered as an expensive issue for the global livestock industries. Recently, in connection with the concern of global warming, research on feeding management of ruminant livestock during summer heat exposure is drawing more attention. In terms of nutrient intake and digestibility, dietary roughage is more vulnerable to thermal stress than concentrate. However, studies related to dietary roughage source on physiological response, and digestive and metabolic functions under heat exposure are scarce. Whereas, whole crop corn silage (WCS) is widely used as a feed for ruminant livestock due to its high starch content, excellent palatability, and better digestibility. Therefore, feeding WCS might improve the physiological response, and digestive and metabolic functions of sheep compared to feeding other roughages under heat exposure. Accordingly, a series of experiments were carried out to clarify the feeding effect of WCS on physiological response, nutrient digestibilities, rumen fermentation characteristics, blood metabolites, protein and energy metabolism in heat exposed sheep compared to other roughages.
The first experiment was conducted with the aim to investigate the potential of feeding WCS diet compared to mixed hay of orchardgrass and reed canarygrass (MH diet) or orchardgrass silage (GS diet) based on their physiological response and digestive functions in heat exposed sheep. Six sheep were fed ad libitum with any of the three diets in a replicated 3×3 Latin-square design for 24 days. After 14 days adaptation, they were exposed to thermoneutral environment (20°C; TN) and then heat exposure (30°C; HE) with 70% relative humidity (RH) for 5 days each. Rumen fermentation characteristics were performed on day 4, while physiological response and nitrogen (N) balance were carried out for three successive days in each exposure period. Respiration rate (RR) and rectal temperature (RT) of WCS fed sheep were lower (P<0.05) than of MH and GS fed sheep and both were higher (P<0.01) during heat exposure. The intakes of DM and N and the digestibilities of N and neutral detergent fiber (NDF) were lower (P<0.05) for WCS diet than for MH and GS diets and they did not differ between two environmental.