Protein supply and methane emission in dairy cows

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

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Abstract

Among the aims in ruminant nutrition research, improving N efficiency and reducing methane emission are two of the most important ones at present, especially under the situation of global climate changing increasingly. This thesis aims to improve N efficiency and mitigate methane emission in dairy cows at the same time, and to investigate the relationship between N supply, nitrate supplementation, genetic yield index on methane emission, and to investigate the effect of nitrate supplementation on methane and nitrous oxide emission by conducting three studies below.
In paper Ⅰ, two different processing methods (grinded vs. rolled; untoasted vs. toasted) were applied on fava beans to improve the metabolizable protein and energy supply, and two forage sources (75:25 or 25:75 ratio between grass-clover silage and maize silage) were examined combined with the fava beans processed by three different methods for the effect on rumen fermentation, methane emission and digestion. Six Danish Holstein dairy cows fitted with ruminal, duodenal, and ileal cannulas were used in a 6 × 4 incomplete Latin square design with 4 periods of 21 d duration. Cows were fed ad libitum with 6 experimental diets: diets high in either grass-clover silage or corn silage were combined with ground untoasted, ground toasted, or rolled untoasted fava beans. Cr2O3 and TiO2 were used as flow markers for calculating nutrient digestibilities, gas exchange were measured by respiration chamber in the last 4 d of each period. In paper Ⅱ, three maize feeds (maize meal, maize gluten, and maize gluten feed) were used to formulate diets with three dietary protein levels (147, 153, and 158 CP g/kg DM), nitrate and urea supplementation were applied to examine effects of dietary protein level and nitrate supplementation on N metabolism and methane emission and their interactions. Forty-eight intact Danish Holstein dairy cows were used in a 6 × 4 incomplete Latin square design with 4 periods of 21 d duration. Six diets were formulated in a 2 × 3 factorial arrangement with 3 different dietary protein levels (low (Low), medium (Med), high (High)) combined with either urea (Urea) or nitrate (Nitrate) addition. TiO2 was used as flow markers for measuring nutrient digestibilities and gas exchange was measured by four GreenFeed units in the last 7 d of each period. In paper Ⅲ, urea and nitrate supplementation were applied to four Danish Holstein dairy cows fitted with ruminal cannula to investigate the effect of nitrate supplementation on ruminal methane and nitrous oxide emission. Cows were used in a 2 × 2 crossover design with 2 periods of 14 d duration. Gas exchange was measured by respiration chamber from d 11 to d 14 of each period and rumen headspace gas samples were collected at d 12 and d 14 in each period for analyzing ruminal headspace methane and nitrous oxide concentrations.
It was concluded in paper Ⅰ that neither forage source, nor rolling and toasting of fava beans affected on MP supply. Compared with grinding, rolling of fava beans reduced ruminal fermentation and apparent ruminal and total-tract digestibility of nutrients, except for NDF, where digestibility was increased. Rolling of fava beans also reduced the microbial protein synthesis compared with ground untoasted fava beans. Toasting of fava beans had no effect on digestibility, except for an interaction with forage source on DM and OM apparent ruminal digestibility. Results from paper Ⅱ shows that there is no interaction between dietary protein level, nitrate supplementation, and genetic yield index on methane emission. Increased dietary protein level by reducing the proportion of corn meal and corn gluten, and increasing the proportion of corn gluten feed in the diet resulted in a decreased milk yield but CH4 production was unaffected. The reduction in DMI, CH4 production, and yield of milk protein and lactose, and the increase in H2 production caused by nitrate supplementation were greater in multiparous cows than in primiparous cows. DMI and ECM were positively correlated to genetic yield index, while CH4 production, CH4 yield, and CH4 intensity were unaffected by genetic yield index. In paper Ⅲ, the results shows that with a dose of 10 g NO-¦3 per kg of DM addition, nitrate supplementation reduced CH4 production and yield and tended to reduce CH4 intensity, and increased H2 production and yield compared with urea supplementation. Nitrate supplementation also reduced N2O headspace volume proportion in the rumen and N2O production compared with urea supplementation.
This thesis shows that forage source and processing methods on fava beans applied in this project had no effect on MP supply. Dietary protein level had no effect on the methane emission and methane mitigation effect of nitrate supplementation, nitrate supplementation results in a greater increase in H2 multiparous cows than in primiparous cows, and nitrate supplementation reduced methane emission but increased N2O production.
OriginalsprogEngelsk
ForlagAarhus University
Antal sider159
StatusUdgivet - jan. 2023

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