UNIVERSIDAD DE BUENOS AIRES FACULTAD DE CIENCIAS...
Nitrate decreases ruminal methanogenesis through competition with hydrogenotrophic\nmethanogens for available hydrogen (H2), and also by its toxic effects on methanogens, but there\nis limited knowledge of its effects on other members of the ruminal microbiota and their metabolites. The general obje...
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
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Universidad de Buenos Aires. Facultad de Ciencias Veterinarias
2021
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=avaposgra&cl=CL1&d=HWA_7064 https://repositoriouba.sisbi.uba.ar/gsdl/collect/avaposgra/index/assoc/HWA_7064.dir/7064.PDF |
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| Sumario: | Nitrate decreases ruminal methanogenesis through competition with hydrogenotrophic\nmethanogens for available hydrogen (H2), and also by its toxic effects on methanogens, but there\nis limited knowledge of its effects on other members of the ruminal microbiota and their metabolites. The general objective of this thesis was to evaluate the effect of nitrate inclusion on\nenteric methane (CH4) emission, ruminal microbiota and ruminal metabolism in Holstein calves. To develop this objective, first, an in vitro study was performed to demonstrate its\nantimethanogenic effect and its implications on digestibility and ruminal fermentation in diets of\nlow nutritional quality. Then, an in vivo study using Holstein calves was developed to evaluate the\neffects of nitrate inclusion in the diet on enteric CH4 emission, feed intake, ruminal fermentation\ndynamics, temporal changes in ruminal microbiota (at 0, 4, and 8 h post-feeding), and finally, the effects on biochemical, hematological and blood gases parameters in response to a progressive\ninclusion scheme of nitrate in the diet. Results of the in vitro study: Dry matter digestibility (DMD) and organic matter digestibility (OMD) of the urea + molasses (UME) and nitrate + molasses (NME) treatments were significantly\nincreased compared to the control treatment (CTR) (P<0.001). The NME treatment, compared to\nUME and CTR, decreased CH4 production (g/kg DMD) by 62% and 64%, respectively. Ruminal\npH and total volatile fatty acid (VFA) production did not differ between treatments (P>0.05). The\nNME and UME treatments increased ruminal ammonia concentration (NH3-N) compared to the\nCTR treatment (P<0.01). The NME treatment induced a higher proportion of acetate, but a lower\nproportion of propionate, butyrate, and valerate compared to the UME and CTR treatments (P<0.001).\nResults of the in vivo study: Dry matter intake (DMI), initial and final weight, body weight gain (BWG) and feed conversion did not differ between dietary treatments (P>0.05). Diets containing\nnitrate (NIT) decreased CH4 emission by 27% (g/day), yield by 21% (g/kg of DMI), and intensity by 23% (g/kg of BWG) compared to the control diet (CTR; P<0.05). Ruminal pH and total VFA\nconcentration did not differ between dietary treatments (P>0.05), but they differed with time postfeeding (P<0.05). NH3-N and acetate concentrations increased at 4 h post-feeding, while propionate decreased with the NIT diet (P<0.05). Feeding the NIT diet reduced the populations of total bacteria, total methanogens, Ruminococcus albus and Ruminococcus flavefaciens, and the abundance of Succiniclasticum, Coprococcus, Treponema, Shuttlewortia, Succinivibrio, Sharpea, Pseudobutyrivibrio, and Selenomona (P<0.05); whereas, the populations of total fungi, protozoa,\nFibrobacter succinogenes, Atopobium, and Erysipelotrichaceae L7A_E11 increased (P<0.05).Methemoglobin and deoxyhemoglobin increased according to nitrate concentrations in the diet (P<0.05), on the contrary, oxyhemoglobin and carboxyhemoglobin decreased (P<0.05).\nHematocrit levels decreased (P<0.05), whereas, albumin, alanine aminotransferase (ALT) and gamma-glutamyl transpeptidase (GGT) concentrations did not change (P>0.05). However,\nglucose, urea, aspartate aminotransferase (AST), and retinol concentrations increased (P<0.05)\naccording to nitrate concentrations in the diet.\nIn conclusion, in the in vitro study, the inclusion of nitrate and urea increased the digestibility of Rhodes grass hay, but only the nitrate reduced CH4 production substantially (~60%). Although the inclusion of nitrate induced a lower proportion of propionate, butyrate, and valerate, the digestibility of the substrates was not negatively influenced. In the in vivo study, the ability of nitrate inclusion in the diet to reduce enteric CH4 emission and CH4 yield was confirmed without significantly affecting DMI or BWG. The lower enteric CH4 emission in response to nitrate feeding was over\nthe stoichiometrically predicted reduction potential and also associated with a lower density of total methanogen population, suggesting a predominantly direct effect on ruminal\nmethanogenesis. The decrease in the proportion of propionate in the ruminal fluid in response to\nnitrate was associated with a reduction in the abundance of bacteria involved in the succinate and acrylate metabolic pathways to propionate synthesis. Finally, a dose-response effect was\nobserved for methemoglobin, glucose, urea, AST, and retinol, but these values did not exceed\nreference values. These results highlighted the importance of using a scheme of progressive\ninclusion of nitrate in the diet of calves to reduce the risks of nitrate and nitrite toxicity, and in turn reduce enteric CH4 emissions |
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