Browsing by Person "Sainz-Sanchez, Pedro Alan"

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Rumen fermentation, microbial protein synthesis, and nitrogen balance in tropical cattle fed cultivated forages
(2024) Sainz-Sanchez, Pedro Alan; Dickhöfer, Uta
Over the past decade, extensive research has focused on the role of cultivated forages in cattle diets and their effects on animal performance, particularly in terms of milk yield and daily live weight gain. Despite this progress, there remains a scarcity of information regarding the dietary factors influencing the efficiency of ruminal microbial crude protein (MCP) synthesis and nitrogen (N) balance in tropical cattle fed on cultivated forages. In the Tropics and Subtropics, a variety of non-structural carbohydrate (NSC) sources are commonly used as energy supplements for tropical cattle. Current advancements in ruminant nutrition highlight the need for a deeper understanding of the complex interactions between the type of NSC, the kinetics of starch degradation, and the timing of supplementation, particularly in the context of high-quality forage diets. Hence, the overall objective of the thesis was to comprehensively understand the dietary factors influencing the rumen MCP synthesis and N balance in tropical cattle fed on high-quality and low-quality cultivated forages. This doctoral thesis hypothesized that the rumen MCP synthesis and the N balance in tropical cattle are mainly affected by the crude protein (CP) and fiber concentrations of cultivated forages. It was further hypothesized that dietary factors such as the supplementation of NSC, type of NSC, and time of supplementation influence the nutritional quality of cultivated forages and affect the rumen MCP synthesis and excretion in tropical cattle. Overall, one in vitro and two in vivo studies were conducted to investigate the proposed hypotheses. In the first in vivo study (Chapter 2), three forage grass species (Cenchrus purpureus, Chloris gayana, and Urochloa brizantha), grown alone or intercropped with a forage legume (Dolichos lablab), were evaluated to determine feed intake, digesta passage rates, rumen MCP synthesis, and N balance in Boran steers. The results showed similar duodenal MCP flow, MCP synthesis efficiency, and digesta passage rates in steers fed different forage grasses, whether grown alone or intercropped. Minor variations in dry matter (DM) intake largely drove increased N intake, fecal N excretion, and N balance, particularly when no significant differences in the chemical composition of the forage grass species were observed. The in vitro study (Chapter 3) evaluated the interactions between tropical forage grasses (Urochloa humidicola and Urochloa mutica) and forage legumes (Desmodium uncinatum, Stylosanthes guianensis, and Mucuna pruriens) and their effects on in vitro total gas production (TGP), short-chain fatty acids (SCFA) concentration and profile, and MCP synthesis. For this, various forage-legume mixtures were prepared by varying the ratios of forage legume to forage grass (75:25 or 25:75 on DM basis). Results indicated that in vitro TGP, short-chain fatty acids concentration and profile, and MCP synthesis were influenced by CP concentration, CP degradation extent, and the fermentation of both structural and NSC of the forages. Additionally, supplemental CP and NSC, influenced in vitro TGP and MCP synthesis. The second in vivo study (Chapter 4) evaluated the use of corn and oat, differing in extent and rate of ruminal starch degradation as NSC sources (i.e., corn- and oat-based concentrate mixtures), supplemented to lactating Brown Swiss cows before or after grazing on an alfalfa-ryegrass sward. The study measured feed intake, rumen MCP synthesis, nutrient digestibility, N partitioning, and milk performance. Supplementing corn-based concentrate mixture after grazing and oat-based concentrate mixture before grazing improved the efficiency of MCP synthesis, milk performance, and efficiency of N use in grazing lactating dairy cows. The effects of NSC supplementation were influenced by the interdependent interactions of starch concentrations of NSC sources, their ruminal degradation kinetics, and the timing of supplementation. The findings of the present thesis, supported by existing literature, demonstrate that cultivated tropical forages can provide sufficient N compounds to support rumen MCP synthesis, meeting the CP requirements of tropical cattle without negatively affecting DM intake, nutrient digestibility, N balance, or overall animal performance. Although CP concentration of the cultivated forages is a key factor influencing rumen MCP synthesis and N balance in tropical cattle, this perspective overlooks important aspects such as the distinction between rumen degraded protein and rumen undegraded protein which provide a clearer representation of CP degradation and utilization at both, the ruminal and post-ruminal levels. The CP concentration in cultivated tropical forages is not the only factor affecting N balance; other nutritional factors, such as energy concentration, neutral detergent fiber, and acid detergent fiber concentrations, also play a crucial role. Specifically, the energy concentration of the forage affects the capture of N by ruminal microbes, while the concentrations of neutral detergent fiber and acid detergent fiber influence the available energy in the forage, thereby impacting overall N utilization in tropical cattle. The interaction between the time of supplementation and the type of NSC source influences the synchronization of N and energy in the rumen. The response to NSC supplementation is influenced by the timing of supplementation and the degradation rates of CP and carbohydrates in both the forages and NSC sources. In the context of the results presented in the present thesis and the existing literature, cultivated tropical forages not only enhance protein nutrition and performance in tropical cattle but may also contribute positively to environmental sustainability. For instance, reducing urinary and fecal N excretion helps limit excessive N release into the environment. Additionally, intercropping forage legumes with grasses can enhance soil fertility and improve soil structure. However, further research is required to assess overall system sustainability and to develop comprehensive feeding strategies for tropical cattle in the Tropics and Subtropics.