Enteric Methane Emissions, Rumen Fermentation Characteristics, and Energetic Efficiency of Holstein Crossbred Bulls Fed Total Mixed Ration Silage with Cassava instead of Rice Straw

This study investigated the effects of substituting rice straw with cassava in total mixed ration silage on feed intake, digestibility, rumen fermentation, ruminating activity, and energy balance. An energy balance experiment was conducted to determine nutrient and energy utilization in dairy bulls. Four Holstein Friesian (HF) crossbred young bulls (93.19% HF x 6.81% Native Thai; average age of 12.08 +/- 0.22 months and body weight of 266 +/- 9.80 kg) were used in a 4 x 4 Latin square design with four 28-d periods. The four dietary treatments included substituting cassava with rice straw on a 50, 150, 250, and 350 g/kg dry matter basis. Increasing the amount of cassava in the diet resulted in linearly decreased rumination behaviors and enteric methane emissions (p < 0.05) but a linear increase in feed intake and digestibility, total volatile fatty acid concentration, and propionic acid: acetic acid ratio in the rumen fluid (p < 0.05), thus leading to a greater energy balance status (p < 0.01). Our results indicated that replacing cassava with rice straw from 5% to 35% in the ration of Holstein bulls resulted in a substantial reduction in physically effective fiber and chewing time but improved nutrient and energy supply. The metabolizable energy requirement for the maintenance of crossbred dairy bulls was estimated to be 599.9 kJ/kg metabolic body weight and the efficiency of metabolizable energy used for growth was 0.88. We concluded that cassava is a good energy feed resource for Holstein crossbred bulls in the tropics.