improving the efficiency of dietary protein utilization in dairy cows and reducing ammonia emissions from manure

Open Access
Author:
Lee, Chanhee
Graduate Program:
Animal Science
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 26, 2012
Committee Members:
  • Alexander Nikolov Hristov, Dissertation Advisor
  • Alexander Nikolov Hristov, Committee Chair
  • Gabriella Anne Varga, Committee Member
  • Kevin John Harvatine, Committee Member
  • Curtis James Dell, Committee Member
  • Gary W Feyereisen, Special Member
Keywords:
  • metabolizable protein
  • coconut oil
  • rumen-protected amino acids
  • NH3 volatilization
  • manure
  • dairy cow
Abstract:
Experiments were carried out to investigate the effects of a low-protein diet on nitrogen (N) utilization and production in dairy cows and ammonia and greenhouse gas (GHG) emissions from manure. The objective of the first experiment was to investigate the effects of a low-protein diet [metabolizable protein (MP) below the requirements (NRC, 2001)] and coconut oil supplementation on N utilization and production in lactating dairy cows. The hypothesis was that a partial defaunation of the rumen by feeding coconut oil would increase microbial protein synthesis in the rumen, thus compensating for potential MP deficiency. The experiment lasted for 10 wk with 36 cows in a randomized complete block design. Cows were fed a MP-adequate diet (AMP), a MP-deficient diet (DMP), or DMP supplemented with coconut oil (DMPCO). Supplementing with coconut oil decreased rumen protozoal counts up to 60% compared with DMP. Milk yield was decreased by DMP compared with AMP. The DMPCO further decreased milk yield as a consequence of depressed dry matter intake (DMI). The DMP- diets increased the efficiency of dietary N utilization for milk protein synthesis (milk protein-N ÷ N intake) by reducing urinary N excretion compared with AMP. Overall, the MP-deficient diets decreased N losses, but also decreased milk production. Supplementation with coconut oil decreased feed intake and therefore could not have a positive impact on milk production in this experiment. The objective of the second study was to investigate the effects of feeding a low-protein diet supplemented with rumen-protected (RP) Met on dairy cow performance and ammonia emissions from manure. Two experiments were carried out. In experiment 1, 36 dairy cows were fed the AMP, DMP supplemented with RPLys (DMPL), or DMPL supplemented with RPMet (DMPLM) diets. In experiment 2, 120 Holstein cows were grouped in pens of 20 cows and were fed AMP supplemented with RPLys (AMPL), or AMP supplemented with RPMet (AMPLM). Each experimental period lasted for 10 wk (2 wk adaptation and 8 wk experimental periods) following a 2-wk covariate period. The hypothesis of the first experiment was that a MP-deficient diet supplemented with RPMet would sustain milk production and composition similar to a MP-adequate diet, provided Lys requirements were met, with the environmental benefits of reduced N excretion. The hypothesis tested in the second experiment was that RPMet supplementation would increase milk and milk protein yields in cows fed MP-adequate, but Met-deficient diet. The MP-deficient diets had no effects on DMI and milk yield. Compared with AMP, DMPL decreased milk protein content and milk protein yield, but DMPLM showed no statistical difference in milk protein content. Urinary N losses decreased with the DMP- diets compared with AMP. Plasma Lys and Met concentrations were not affected by treatment while His concentration was lower for the DMP- diets compared with AMP. In Exp. 2, the AMPLM diet resulted in lower milk yield than AMPL due to a numerical decrease in DMI while no other production effects were observed. Overall, feeding MP-deficient diets, supplemented with RPLys and RPMet sustained milk yield in dairy cows in this experiment. However, without RPMet supplementation, milk protein content was decreased compared with AMP. Based on plasma amino acids (AA) profile, we concluded that His may be limiting milk production in MP-deficient, corn silage and alfalfa haylage-based diets. There were no production benefits of supplementing the AMP diet with RPMet. The objective of the third experiment was to investigate the effects of a low-protein diet supplemented with RPHis in addition to RPLys and RPMet on N utilization and cow performance. The hypothesis of this experiment was that feeding the MP-deficient diet supplemented with RPHis in addition to RPLys and RPMet would sustain milk production of dairy cows similar to AMP with environmental benefits by decreasing N losses. The experiment was conducted for 10 wk following a 2-wk covariate period with 48 lactating dairy cows fed 4 treatment diets: AMP, DMP, DMPLM and DMPLM supplemented with RPHis (DMPLMH). Compared with AMP, DMI tended to be lower with the DMP diet but was similar for the DMPLM and DMPLMH diets. Milk yield was decreased by DMP, but was similar to AMP for the DMPLM and DMPLMH diets, following the trend in DMI. Milk protein yield followed the trend in milk yield response and was not different from AMP for the DMPLM and DMPLMH diets. In conclusion, DMP decreased DMI and milk yield in dairy cows. Supplementating with RPLys and RPMet diminished the difference in milk yield compared with AMP, and addition of RPHis eliminated the difference. This experiment indicated that His is likely one of the limiting AA in dairy cows fed MP-deficient diets. The objective of the fourth experiment was to investigate the effects of a low-protein diet on ammonia (NH3) and greenhouse gas (GHG; nitrous oxide, methane, and carbon dioxide) emissions from fresh dairy cow manure incubated in controlled storage conditions (Experiment 1) and from manure-amended soil (Experiment 2). Feces and urine were obtained from the cows fed AMP and DMP diets. Manure was produced by mixing feces and urine (1.7:1) immediately before incubation (Exp.1) and application to lysimeters containing soil (a Hagerstown silt loam; fine, mixed, mesic Typic Hapludalf) (Exp. 2). In Exp. 2, manure was applied to 21 lysimeters (including 3 blank lysimeters: without manure) at 277 kg of N/ha application rate. In Exp. 1, cumulative emissions and emitting potential (EP) of NH3 were greater for AMP compared with DMP manure. The EP and cumulative emissions of GHG were not different between AMP and DMP manure. In Exp. 2, the NH3 EP was greater for lysimeters amended with AMP than with DMP manure. The EP of methane was increased and that of carbon dioxide tended to be increased by DMP compared with AMP manure. The cumulative carbon dioxide emission was increased with manure from the DMP diet. Nitrous oxide emissions were low in this experiment and did not differ between treatments. In conclusion, fresh manure from dairy cows fed a low-protein diet had substantially lower NH3 EP, compared with manure from cows fed a high-protein diet. The DMP manure increased soil methane EP due to a greater mass of manure added to meet plant N requirements compared with AMP manure. Lastly, a series of laboratory experiments were conducted to establish the relationship between N isotope composition of cattle manure and NH3 emissions, potential contribution of nitrogenous gases other than NH3 to manure N volatilization losses, and to determine the relative contribution of urinary- vs.fecal-N to NH3 emissions during the initial stage of manure storage. Intensive NH3 volatilization losses from manure coincides with a very rapid loss of urinary urea. The dynamics of manure- and emitted NH3-δ15N indicated that the intensive N isotope fractionation occurred during NH3 volatilization. The experiments demonstrated that the main source of NH3-N volatilized from cattle manure is urinary-N, representing on average 90% of the emitted NH3-N. The contribution of fecal-N was relatively low, but gradually increased to about 10% by day 10. There appears to be substantial emissions of nitrogenous gases other than NH3, most likely dinitrogen gas, which may account for up to 25% of N losses. This finding may be indicative of overestimation of NH3 emissions from cattle operations by the current emissions factors.