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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #289997
Title: Feed conversion efficiency in dairy cows: Repeatability, variation in digestion and metabolism of energy and nitrogen, and ruminal methanogens

Author
item ARDNT, C - University Of Wisconsin
item Powell, Joseph
item AGUERRE, M - University Of Wisconsin
item CRUMP, P - University Of Wisconsin
item WATTIAUX, M - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2015
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62913
Citation: Ardnt, C., Powell, J.M., Aguerre, M.J., Crump, P.M., Wattiaux, M.A. 2015. Feed conversion efficiency in dairy cows: Repeatability, variation in digestion and metabolism of energy and nitrogen, and ruminal methanogens. Journal of Dairy Science. 98(6):3938-3950.

Interpretive Summary: In an effort to find ways to reduce greenhouse gas emissions from dairy production systems, research must be conducted with lactating cows which is quite expensive. More accurate low-cost methods are needed to measure and monitor greenhouse gas emissions from various components of dairy production systems. This study determined that one cow is sufficient to measure methane, carbon dioxide, nitrous oxide and ammonia emissions from air emission chambers initially designed for four cows. Cows efficient at converting feed to milk were found to also have a higher conversion of dietary nitrogen to milk nitrogen and lower greenhouse gas emission per day, per unit of milk, and per unit of milk energy. The results of this study validated accurate low-cost methods for measuring and mitigating emissions of greenhouse gases and ammonia from dairy barns.

Technical Abstract: More accurate low-cost methods are needed to measure and monitor greenhouse gas (GHG) emissions from various components of dairy production systems. The objectives of this study were to determine the effect of air-flow-controlled chambers, originally designed to house four cows, on emissions of greenhouse gases (CH4, N2O, and CO2) and ammonia (NH3) when accommodating only one dairy cow; and to determine whether partial feed conversion efficiency for milk (pFCEm, kg milk/kg dry matter intake (DMI)) influenced gaseous emissions and nitrogen utilization. Four second-parity cows, two with high pFCEm (means ± SD 1.94 ± 0.11) and two with low pFCEm (1.49 ± 0.05) during the week prior to the study, were selected and housed in each of four chambers in four consecutive periods of four days. Cows were fed a total mixed ration containing 24.5% neutral detergent fiber, 17.1% crude protein, and 56.7% forage (DM basis). Daily measurements included DMI, milk production, milk composition, body weight, and gaseous emissions (CH4, N2O, NH3, and CO2) using a photo-acoustic multi-gas monitor. Data were analyzed as a 4x4 Latin square with chamber as treatment, pFCEm, and period as blocking factors, and days as repeated measures. Partial FCEm (high vs. low) was considered a fixed effect but cow within pFCEm a random effect. Chamber did not affect any of the gaseous measurements. During the 16 days of measurements milk production was 50.5 and 40.2 kg/d whereas DMI was 26.5 and 27.9 kg/d for high pFCEm cows and low pFCEm cows, respectively. Chamber emission of high pFCEm cows were 19% less for CH4 (802 vs. 996 g/d), 12% less for CO2 (26,086 vs. 29,481 g/d), 9% less for N2O (1.11 vs. 1.22 g/d), 32% less for CH4/milk (16.0 vs. 23.6 g/kg), 23% less for CH4/milk energy (25.0 vs. 32.5 g/Mcal net energy for lactation (NEL)), 26% less for CO2/milk (521 vs. 700 g/kg), 16% less for CO2/milk energy (813 vs. 967 g/Mcal NEL), and 24% less for N2O/milk (0.022 and 0.029 g/kg) compared with chamber emissions of low pFCEm cows. Cow pFCEm influenced emission expressed per unit of DMI for CH4 but not the other gases. Milk nitrogen divided by nitrogen intake was 15% higher in high pFCEm than in low pFCEm cows (0.259 vs. 0.225 g/g, respectively), but chamber NH3-N emission was not affected by pFCEm. Future GHG trials may be accomplished with one cow in each chamber and can be designed without blocking for chamber effects. Furthermore, the relationships among pFCEm, greenhouse gas emission, and nitrogen utilization observed in this trial should be explored with more cows.