1519
Estimation of Heat Production and Energy Conversion Efficiency Using Real Time Measurements of Methane and Carbon Dioxide Fluxes in Mid-Lactation Holstein Cows
Real time measurements of CH4 (QCH4) and CO2 (QCO2) fluxes were used in a pilot study to estimate heat production1 (HP) and energy conversion efficiency in lactating dairy cows. Oxygen utilization (QO2) was estimated according to the respiration quotient2. Eleven multiparous and 4 primiparous lactating Holstein cows averaging 176 ± 34 DIM, 42.9 ± 6.8 kg of milk yield and 681 ± 48 kg of BW were blocked by DIM, parity, and DMI (as % of BW) and, within each block, randomly assigned to 1 of 2 treatments: restricted intake (RI) (90% DMI) or ad libitum intake (AI) according to a crossover design. Each experimental period lasted 22 d with 14 d for treatments adaptation and 8 d for data and sample collection. Diets contained (DM basis): 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot gas measurements were taken in 5-min sampling periods from all cows using a portable automated head chamber system [GreenFeed® (GF); C-Lock Inc., Rapid City, SD] with intervals of 12 h between the 2 daily samplings. Sampling points were advanced 2 h from a day to the next to yield 14 gas samplings/cow over 7 d to account for diurnal variation in QCH4 and QCO2. Data were analyzed using the Fit Model procedure in JMP, and least square means are reported. Cows on RI converted more feed gross energy3 into milk energy4 (28.3 vs. 27.0%, SEM = 0.63; P = 0.04) and more DMI into metabolizable energy5 than AI cows (11.8 vs. 11.3 MJ/kg of DMI; SEM = 0.22 P = 0.02). Conversely, RI cows yielded more HP/kg of DMI (6.65 vs. 6.36 MJ/kg; SEM = 0.18; P = 0.04). Our results suggest that the proposed methodology has potential to identify more efficient dairy cows according to real time measurements of QCH4 and QCO2 using the GF.
Equations used for estimations:
1Estimated HP MJ/cow/d = [(3.86 × QO2) + (1.2 × QCO2) – (0.518 × QCH4)] × 4.184/1000 (Brouwer, 1965)
2QO2/QCO2 = 0.95 (Madsen et al., 2010)
3Gross energy intake MJ/cow/d = [dietary CP% × DMIkg × 17 × 0.6] × 4.184 (IPCC, 2006)
4Milk energy MJ/cow/d = [(0.384 × fat%) + (0.223 × protein%) + (0.199 × lactose%) – 0.108] × milk yield kg/cow/d (AFRC, 1993)
5Metabolizable energy MJ/cow/d = HP + Milk energy ± (19.99 × kg of mobilized weight) (AFRC, 1990)
Keywords: energy conversion efficiency, heat production, GreenFeed