Determination of the proportion of the ingested gross energy lost as exhaled methane by dairy goats consuming contrasting concentrate ingredients in mixed rations

Abstract

Twelve 2-yr-old, dry Murciano-Granadina dairy goats were selected and divided into four equal groups based on similar body weight (38.41 ± 0.78 kg). The four treatments were mixed diets with approximately 600 g kg-1 alfalfa hay chopped to 2.5-cm particle size, and 400 g kg-1 of concentrate. The concentrate has 250 g kg-1 of cereal grain (corn or barley) and 150 g kg-1 of protein (sunflower meal or green peas). Experimental diets were isoenergetic with an average value of 18.9 MJ gross energy (GE) kg-1 of dry matter (DM). Apparent digestibility, intake, metabolic energy and methane (CH4) production were obtained. The effect of cereal grain was significant for crude protein (P < 0.001) and acid detergent fiber (P < 0.049) digestibility. The effect of protein source was significant for DM (P < 0.025), organic matter (P < 0.031) and DEI (P < 0.016) digestibilities. CH4 exhaled was determined by an open-circuit mask calorimeter system. An average value of 0.8 L CH4 h-1 was found for these mixed rations. When this was expressed as the proportion of the ingested GE lost as exhaled methane, the average value was 4.6. Because of the non-significant differences observed among these mixed diets studied to determine exhaled CH4 by non-productive dairy goats, diets based on barley and sunflower meal are recommended. These crops are cheaper than corn and peas because they are produced in Spain and not imported from other countries.