Efeito do estresse térmico sobre a seleção de dieta por bovinos / Effect of heat stress on diet selection by bovine

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The effect of heat stress on diet selection of ruminants was studied in a completely randomized design with 12 fistulated dry cows. The trial was conducted in 20 days with two treatments: thermal comfort (open barn, 21°C) and heat stress (climatic chamber, 38°C). Feeds were offered separately and ad libitum and composed by sugar cane + urea (14% CP) and concentrate, based on corn + soybean meal (14% CP). The ability of bovine to select their diets was identified comparing the composition of diet selected, ruminal fermentation parameters and total tract digestibility (chromic oxide as external marker) in different environments. A decrease of 22% in total dry matter intake was observed for animals in heat stress compared to the ones in comfort environment. Concentrate:roughage radio chosen was similar for both treatments. These data suggest that animals decreased dry matter intake without changing energy and fiber concentration in their diets, attempting maintain a stable ruminal environment. There was not difference on total volatile fatty acids production in the rumen, molar percentage of acetate, propionate and butirate, acetate/propionate ratio and ruminal pH. Ammoniacal-N concentration in the rumen was 47% higher for stressed than for comfort animals. This indicates that animals do make wise choices in order to maintain an ideal ruminal environment. However, there was a decrease in digestibility (49% for dry matter, 55% for crude protein, 26% for nitrogen-free extractive, 31% for ether extract, 44% for starch and 52% for gross energy) for animals in stress, reducing the availability of nutrients for bovine.

ASSUNTO(S)

voluntary intake consumo de alimentos ruminantes dieta animal digestibilidade ruminant estresse heat stress diet choice digestibility

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