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A new animal calorimeter using a ventilated hood was constructed in Thailand. The recovery rates of our head cage were 96.5%, 97.0%, 95.7%, and 101.8%. The recovery rates of our head cage (95.7 101.8%) are reliable compared with Japanese whole-body chambers. The 99% CO 2 recovery time of our head cage was an average 14 min. It was shorter than whole-body chambers because of smaller effective volume and higher flow rate. Our head cage system excels at dynamic measurement of heat production. We started accumulating data concerning the energy value of Pangola grass (Digitaria eriantha) using 4 Brahman steers (body weight, 372.8 34.4 kg, mean standard deviation; age, 3 years old). They were fed Pangola grass for 21 days; the grass was harvested approximately 45 days after cutting in several farms around Bangkok. Digestible energy and metabolizable energy of Pangola grass hay in our study were 10.28 and 7.99 MJ/kg dry matter. The average volume of methane production was 228.3 L/day and energy loss in the form of methane was 0.097 of the gross energy intake. These values are acceptable when compared with those obtained when low-quality tropical feed is provided to the steers. Discipline: Animal industryAdditional key words: Brahman steers, digestible energy, metabolizable energy

ObjectiveThis study was conducted to assess the effects of replacing rice straw with different proportions of cassava pulp on growth performance, feed intake, digestibility, rumen microbial population, energy partitioning and efficiency of metabolizable energy utilization in beef cattle.MethodsEighteen yearling Thai native beef cattle (Bos indicus) with an average initial body weight (BW) of 98.3±12.8 kg were allocated to one of three dietary treatments and fed ad libitum for 149 days in a randomized complete block design. Three dietary treatments using different proportions of cassava pulp (100, 300, and 500 g/kg dry matter basis) instead of rice straw as a base in a fermented total mixed ration were applied. Animals were placed in a metabolic pen equipped with a ventilated head box respiration system to determine total digestibility and energy balance.ResultsThe average daily weight gain, digestible intake and apparent digestibility of dry matter, organic matter and non-fiber carbohydrate, total protozoa, energy intake, energy retention and energy efficiency increased linearly (p<0.05) with an increasing proportion of cassava pulp in the diet, whereas the three main types of fibrolytic bacteria and energy excretion in the urine (p<0.05) decreased. The metabolizable energy requirement for the maintenance of yearling Thai native cattle, determined by a linear regression analysis, was 399 kJ/kg BW0.75, with an efficiency of metabolizable energy utilization for growth of 0.86.ConclusionOur results demonstrated that increasing the proportion of cassava pulp up to 500 g/kg of dry matter as a base in a fermented total mixed ration is an effective strategy for improving productivity in zebu cattle.