Measurements of methane emissions and energy and nitrogen utilisation for quantifying the carbon footprint of young Holstein cattle

Abstract

The desire to develop national greenhouse gas (GHG) emission inventories and mitigation strategies to reduce carbon footprint of cattle production systems, has prompted interest to fill the knowledge gap of GHG emission from young cattle in the UK. The current UK government funded study was undertaken over a two-year period to evaluate the effects of gender (steers vs. heifers) of growing Holstein cattle (6 to 22 months of age) on enteric methane emissions and energy and nitrogen utilisation and then to use these data to develop prediction models for quantification of carbon footprint of the dairy production sector.

Twenty 5-month old Holstein cattle (10 steers and 10 heifers) were used in successive 28 d feeding period, with measurements undertaken at age of 6, 12, 18 and 22 months, to investigate the effects on feed intake, live weight gain, energy and nitrogen (N) utilisation and enteric methane (CH₄) emission. Throughout the study, cattle were offered a diet for ad libitum intake containing a single perennial ryegrass silage mixed with concentrates. In the first period, the concentrate supplement was offered at a ratio of 550 g/kg of dry matter (DM), while it was given at a fixed rate of 2 kg DM daily in other 3 periods. During each measurement period, the cattle were housed as a single group in cubicle accommodation for the first 20 d, then individually in metabolism units for the next 3 d, and then in indirect open-circuit respiration calorimeter chambers for the final 5 d with feed intake, faeces and urine outputs and gaseous exchange measured during the last 4 d.

There was no difference (P > 0.05) in animal performance, energy metabolism, CH₄emission, and N utilisation in any period between the gender groups. The data from the two groups were therefore pooled to develop relationships between metabolisable energy (ME) intake and energy balance. The derived NE (NEm) and ME (MEm) requirements for maintenance were greater for cattle at age of 6 months than at age of 12, 18 and 22 months. The corresponding NEm and MEm values derived from all data across the four periods were 0.43 and 0.60 MJ/kg⁰.⁷⁵, respectively. A range of prediction equations on daily CH₄ emissions, N and organic matter (OM) excretion in manures were developed using LW, feed intake or energy intake. Data were further used to calculate yearly accumulated CH₄ emissions, nitrogen and OM excretion in manures, and also to develop a range of prediction equations on accumulated CH₄ emissions, nitrogen and OM excretion in manures. On average, the accumulated CH₄ emissions were 36.2 and 64.3 kg/year in year 1 and 2, respectively, and the accumulated N excretions in faeces were 11.4 and 21.1 kg and in urine 11.6 and 30.6 kg, respectively; the corresponding values for accumulated OM excretions were respectively 241.5, 565.7, 30.3 and 81.5 kg. The data obtained in the present study indicate that total carbon dioxide equivalent for Holstein steers and heifers ranged from 1136 to 1205 kg and 2143 to 2424 kg during the 1ˢᵗ and 2ⁿᵈ year of their lives, respectively.

The present study has generated a range of novel information on maintenance energy requirement, CH₄ emissions and N and OM excretion for growing Holstein cattle. These data have the potential to help improve animal production efficiency and develop robust mitigation strategies to reduce nitrate and carbon footprints for cattle production systems. The reduction of environmental footprint is essential for development ofsustainable dairy and beef production systems in UK.

Date of Award	Oct 2013
Original language	English
Sponsors	Chinese Scholarship Council
Supervisor	Tianhai Yan (Supervisor), David McDowell (Supervisor) & Patrick Naughton (Supervisor)