Effects of Consuming Different Quality Diets and Animal Sex on Digestion and Energy Usage in Dromedary Camels, Using Heart Rate as an Indicator for Energy Expenditure

Thirty-two adult dromedary camels, half males and half females, were employed to study the effects of feed quality and sex on digestion and energy utilization. Animals of each sex were randomly divided into two feeding treatments, including different concentrate-to-roughage ratios of 65:35% (high concentrate) or 35:65% (low concentrate) of concentrate feed and alfalfa hay, respectively. Animals were individually housed in two sets of 16 each, with 4 animals per treatment and sex for each set. Each set consisted of 21 days for adoption, 7 days for collection, and 2 days for gas exchange. Animals were fitted with a face mask facilitating open-circuit respiration for measuring O₂ consumption, while heart rate (HR) monitors were simultaneously measured to determine the individual energy expenditure (EE)/HR ratio. Although a comparable total intake was found between feeding treatments, animals fed a high-concentrate diet had higher nutrient digestibility, except for fiber digestibility, with males digesting nutrients more efficiently than females. However, EE was greater for a low- vs. high-concentrate level, regardless of animal sex. This resulted in a greater energy balance for the high- vs. low-concentrate diet. Similar values for EE were observed between both sexes, with a greater digestible energy intake for males vs. females that was reflected in a greater energy balance, respectively. The EE/HR ratio was consistent across feeding treatments and sexes, with no interaction between them, which is considered a solid indicator for validating HR as a predictor of EE in dromedary camels.