| The emission of methane (CH4) and nitrogen in the lactating cattle raising not only results in fodder energy waste but also may cause local environment pollution. What is more, as greenhouse gases, methane and nitrogen are important sources to the global warming. Thus, by conducting a research on effects of diet composition on CH4 and nitrogen emissions from lactating cattle, the current study aims to propose a mechanism of comprehensive effects of different fodder on CH4 and nitrogen emissions and at the same time to offer reference for the editing of a national list of nitrogen emission from ruminants. Moreover, the current study tries to put forward an advanced method which can help to improve the quality of stock raising and to alleviate the pressure of dairy farming on the environment, too.Based on the three different test diets of Straw Diet Group A in which the ratio of fine fodder against coarse fodder was 40:60 (the coarse fodder is only dry corn stalks), Silage Diet Group B in which the ratio of fine fodder against coarse fodder was 40:60 (the coarse fodder is only corn stalk silage) and Silage Diet Group C in which the ration of fine fodder against coarse fodder was 60:40 (the coarse fodder is only corn stalk silage), and by adopting the vitro fermentation in batches method and SF6 tracer method, the current study is carried out to test the effects of diet composition on CH4 emission from and rumen fermentation traits of lactating cattle. Meanwhile, metabolic method is also used in this study to test the effects of different diets on nitrogen emission from lactating cattle.The vitro fermentation in batches test in laboratory showed that the pH, acetic acid and butyric acid concentration, acetic acid / propionic acid, gas production, CH4 output of Group A, Group B and Group C at all incubation time points after feeding (2h, 4h, 8h, 12h, 18h, 24h, 36h, 48h, 60h, 72h, 84h, 96h) exhibited Group A> Group B> Group C, but the concentration of ammonia nitrogen (NH3-N) and propionic acid exhibited Group C> Group B> Group A. During the process of 96-hour vitro fermentation, the test showed a dynamic change: within 2h-36h, pH decreased with the incubation time but after 36h, it began to exhibit a trend of increase; the concentration of ammonia nitrogen (NH3-N) at all time points first increased and then decreased and finally increased again; the amount of volatile fatty acids (VFA) within 2h-36h increased with time but after 36h exhibited a downward trend; gas production increased with the incubation time, but from the time point of 60h, it began to increase at a slower pace; CH4 output of Group A, Group B and Group C all reached the maximum at the time point of 48h after feeding. The research result also showed that the amount of CH4 output in the three diet groups decreased with the increase of digestibility of dry-matter and the digestible energy.The SF6 tracer test under production conditions showed that the CH4 output of Group A, Group B and Group C were respectively 353L/d, 283 L/d)and 263 L/d, and the difference between Group A and Group B, Group C were extremely significant (p﹤0.05)while the difference between Group B and Group C was insignificant (p﹥0.05); the difference of pH in rumen fluid among all the three groups were significant (p﹤0.05); the concentration of NH3-N were respectively 11.56 mg/dL,13.10 mg/dL,13.70 mg/dL and the difference among all the three groups were significant (p﹤0.05); the concentration of propionic acid were respectively 16.75 mmol/L,17.29 mmol/L,21.25 mmol/L, and the difference among all the three groups were insignificant (p﹥0.05). The milk production of Group A, Group B and Group C were respectively 10.73kg,12.56 kg,12.97 kg, and the difference among all the three groups were insignificant (p﹥0.05); as for the milk composition, the difference of lactose percentage and butter-fat percentage among all the three groups were insignificant( p﹥0.05); however, the difference of dry milk matter percentage and lactoprotein percentage among all the three groups were significant (p﹤0.05).Both the vitro fermentation in batches test and the SF6 tracer test under production conditions showed the silage treatment of corn stalks and an appropriate increase in the proportion of fine fodder in the diet not only could reduce the methane emission from the lactating cattle but also could improve the production performance of the cattle. Meanwhile, these measures would not lead to any unusual rumen fermentation of the lactating cattle.The metabolic test under production conditions showed that the production of fecal nitrogen from lactating cattle were respectively 82.49g/d,81.02 g/d,88.55 g/d in all the three groups, and difference among them were insignificant (p﹥0.05); the nitrogen digestibility in all the three groups were respectively 59.48%,62.14%,69.94%, and the significance among them were significant (p﹤0.05); the urinary nitrogen output in all the three groups were respectively 26.22 g/d,58.15g/d,104.82 g/d, and the significance among them were extremely significant (p﹤0.01).The percentage of energy loss in the form of feces, urine and methane in all the three groups respectively accounted for 51.65%,42.63%,41.05% of the total fodder energy intake. The results showed that the silage treatment of straw corn stalks or appropriate increase of fine fodder in the diet can help to reduce the energy loss of the fodder. |
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