- Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences
Huhtanen, Pekka; Huuskonen, Arto
Cattle farming is an important agricultural contributor to methane (CH4) emissions and has also a significant environmental impact through nutrient surpluses onto arable land. Therefore, the purpose of the present study was to model the effects of carcass weight (CW) and dietary concentrate and protein levels on the CH4 production and nitrogen (N) and phosphorus (P) excretion of daisy bulls fed grass silage-based diets. The modelling was based on treatment mean data from a growing cattle feeding experiment in which the concentrate and protein supply was manipulated. The three concentrate proportions were 300 (LC), 500 (MC) and 700 (HC) g/kg dry matter (DM) fed without (LP) or with (HP) rapeseed meal (RSM) supplementation. In the LP and HP diets the crude protein content of the concentrate was 128 and 160 g/kg DM, respectively. Methane emissions and faecal N output were predicted by the dynamic and mechanistic Karoline model. Manure P was calculated as P intake - Retained P. Predicted differences between the diets in CH4 emissions were small; the greatest difference was approximately 4% lower CH4 intensity expressed per kg carcass weight gain (CWG) in cattle fed HC diet compared with those fed LC or MC diets. Total N intake decreased with increasing diet concentrate proportion, which resulted in reduced urinary and faecal N output and reduced excretions per kg body weight (BW) and CWG. Increased N intake with RSM supplementation resulted in a greater total manure N output per day and per kg 13W and CWG. Most of the increase in manure N output with RSM supplementation was urinary N. Manure P output per day and per kg BW and CWG increased with greater concentrate or protein supplementation. Within the practical range of grass silage-based beef cattle diets fed to dairy bulls the effects of diet composition on methane yield or intensity were small. However, taking into account carbon footprint of feed production, increasing proportion of grain in the diet can increase total carbon footprint. Emissions per unit of CWG markedly increase with increased CW. Manure N and P output and methane emission per unit of CWG increased more rapidly in BW above 570 kg, mainly because of reduced BW gain. Manure N and P output per kg CWG were mainly related to dietary concentrations of these nutrients and CW. Decreasing dietary N and P inputs is the best nutritional strategy to reduce manure N and P outputs.
Beef production; Environmental impacts; Methane; Modelling
2020, Volume: 232, article number: 103896
Animal and Dairy Science