Effect of dietary crude protein and forage contents on enteric methane emissions and nitrogen excretion from dairy cows simultaneously

Authors: NIU, M - University Of California; APPUHAMY, J.A.D.R.N. - University Of California; Leytem, April; Dungan, Robert - Rob; KEBREAB, E - University Of California

Submitted to: Animal Production Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2015
Publication Date: 2/9/2016
Publication URL: https://handle.nal.usda.gov/10113/62193
Citation: Niu, M., Appuhamy, J., Leytem, A.B., Dungan, R.S., Kebreab, E. 2016. Effect of dietary crude protein and forage contents on enteric methane emissions and nitrogen excretion from dairy cows simultaneously. Animal Production Science. 56:312-321.

Interpretive Summary: The interaction between dietary crude protein and forage content and their impact on enteric methane emissions and nitrogen excretion are not experimentally quantified in dairy cows. Cows receiving reduced crude protein diets had low manure nitrogen outputs and improved milk true protein production efficiencies, regardless of dietary forage content. This study provided some insights to understand the relationship between nitrogen and methane excretions, but further studies are needed using more diverse diets to come up with strategies that jointly minimize methane emissions and nitrogen excretions.

Technical Abstract: The study aimed to examine, simultaneously, the effects of changing dietary forage and crude protein (CP) contents on methane (CH4) emissions and nitrogen (N) excretion from lactating dairy cows. Twelve post-peak lactating Holstein cows were randomly assigned to 4 treatments from a 2×2 factorial arrangement of two dietary forage levels [37.4% (LF) vs. 53.3% (HF) of DM] and two dietary CP levels [15.2% (LP) vs. 18.5% (HP) of DM] in a 4×4 Latin square design with four 18 d periods. Alfalfa hay was the sole source of dietary forage. Cows were fed and milked twice daily. During the first 14 d, cows were housed in a free-stall barn, where enteric CH4 emissions were measured using the GreenFeed system from d 8 to 14 in each period. Cows were then moved to metabolic cages, where total feces and urine output (kg/cow/d) were measured using total collection approach for 3 days. No dietary forage by CP interactions were detected for DMI, milk production, enteric CH4 emissions, or N excretions. Dry matter intake, milk production, and milk composition yield were increased by LF diet (P < 0.01). No difference was found between cows fed HP or LP diets, however, milk fat content increased in cows fed HP (P < 0.05). Enteric CH4 emissions, and CH4 per unit of DMI, ECM, total digested OM and NDF were not affected by dietary CP, but decreased by LF compared to HF (P < 0.01). Milk true protein N was not affected by dietary CP content but was higher for LF compared to HF. Greater dietary N was partitioned to true milk protein in cows fed LF compared to HF diet (P < 0.01). Urinary N excretion was greater in cows fed HP (P < 0.01), and lowest in cows fed LF diet (P < 0.01). Neither dietary CP nor forage content affected fecal N. Total N excretion (urinary plus fecal) did not differ between HP and LP, but tended to be lower in cows fed LF compared to HF diet (P = 0.09). Both milk urea N (P < 0.01) and blood urea N (P < 0.01) declined with decreasing dietary CP or forage contents. Based on purine derivative analysis, microbial protein synthesis in the rumen tended to be lower for high forage and low protein treatments (P < 0.09). Increasing dietary forage contents resulted in greater CH4 emission (g/kg of ECM) and manure N excretion (g/kg of ECM) intensities of lactating dairy cows. Cows receiving reduced CP diets had low manure N outputs and improved milk true protein production efficiencies, regardless of dietary forage content.