Chapter 8 Nitrogen metabolism by splanchnic tissues of ruminants

Reynolds, C.K.

doi:10.1016/s1877-1823(09)70015-3

Cited by 4 publications

(7 citation statements)

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“…Microbial protein also includes non-protein N recycled from the blood as urea, but these are not 'endogenous' proteins per se. Measurement of the flow of these endogenous proteins is technically challenging, but available data suggest that they can represent from 8% to 16% of total protein flow to the small intestine (Reynolds, 2005;Lapierre et al, 2006). Therefore, measurements of total flow overestimate the true supply provided by the diet and fermentation.…”

Section: Factors Affecting the Efficiency Of N Utilization In The Pdvmentioning

confidence: 99%

“…milk protein synthesis), in part through changes in arterial concentration. For example, the removal of EAA by the liver relative to their net release by the PDV increases in dry compared with lactating cows (Reynolds, 2005 and2006a), most likely due to lack of protein synthesis in the mammary gland. Reynolds (2002) also reported that when casein is infused into the abomasum and not accompanied by equivalent increases in milk protein secretion, net removal of EAA by the liver also increases.…”

Section: Factors Affecting the Efficiency Of N Utilization In The Pdvmentioning

confidence: 99%

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Strategies for optimizing nitrogen use by ruminants

Calsamiglia

Ferret

Reynolds

et al. 2010

Animal

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The efficiency of N utilization in ruminants is typically low (around 25%) and highly variable (10% to 40%) compared with the higher efficiency of other production animals. The low efficiency has implications for the production performance and environment. Many efforts have been devoted to improving the efficiency of N utilization in ruminants, and while major improvements in our understanding of N requirements and metabolism have been achieved, the overall efficiency remains low. In general, maximal efficiency of N utilization will only occur at the expense of some losses in production performance. However, optimal production and N utilization may be achieved through the understanding of the key mechanisms involved in the control of N metabolism. Key factors in the rumen include the efficiency of N capture in the rumen (grams of bacterial N per grams of rumen available N) and the modification of protein degradation. Traditionally, protein degradation has been modulated by modifying the feed (physical and chemical treatments). Modifying the rumen microflora involved in peptide degradation and amino acid deamination offers an alternative approach that needs to be addressed. Current evidence indicates that in typical feeding conditions there is limited net recycling of N into the rumen (blood urea-N uptake minus ammonia-N absorption), but understanding the factors controlling urea transport across the rumen wall may reverse the balance to take advantage of the recycling capabilities of ruminants. Finally, there is considerable metabolism of amino acids (AA) in the portal-drained viscera (PDV) and liver. However, most of this process occurs through the uptake of AA from the arterial blood and not during the 'absorptive' process. Therefore, AA are available to the peripheral circulation and to the mammary gland before being used by PDV and the liver. In these conditions, the mammary gland plays a key role in determining the efficiency of N utilization because the PDV and liver will use AA in excess of those required by the mammary gland. Protein synthesis in the mammary gland appears to be tightly regulated by local and systemic signals. The understanding of factors regulating AA supply and absorption in the mammary gland, and the synthesis of milk protein should allow the formulation of diets that increase total AA uptake by the mammary gland and thus reduce AA utilization by PDV and the liver. A better understanding of these key processes should allow the development of strategies to improve the efficiency of N utilization in ruminants. Keywords: ruminant, nitrogen efficiency ImplicationsRuminants have a low efficiency of N utilization compared with non-ruminants. This low efficiency has implications not only for production performance and economic efficiency but also for the emission of contaminants to the environment. The efficiency of N utilization can be improved through the understanding and modification of factors regulating the efficiency of N utilization in key processes, including N capture in the rumen, ...

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Section: Factors Affecting the Efficiency Of N Utilization In The Pdvmentioning

confidence: 99%

Section: Factors Affecting the Efficiency Of N Utilization In The Pdvmentioning

confidence: 99%

Strategies for optimizing nitrogen use by ruminants

Calsamiglia

Ferret

Reynolds

et al. 2010

Animal

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260

165

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“…Figure 1. Relationship between N intake and net liver release of urea N in cattle (corrected for random effects of study as described by St-Pierre, 2001; n = 304; for sources of the original data, see Reynolds, 2003). Figure 2.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, feeding steers urea markedly increased net PDV absorption of ammonia and liver urea synthesis, without significant effects on net liver oxygen consumption, glucose release or amino acid metabolism (Maltby et al, 1993). In a methodical series of studies in sheep, Lobley and colleagues have explored effects of increased ammonia absorption on liver metabolism and similarly found no significant deleterious effects on liver metabolism of oxygen, glucose or amino acids (see Lobley et al, 1995;Milano and Lobley, 2001;Milano et al, 2000;Reynolds, 2003). Despite ranging from 67 to 102 g/d of urinary N excretion (data not shown), N excretion in urine is a minor proportion of digestible energy intake ( Table 1).…”

Section: 2mentioning

confidence: 99%

“…Oba and Allen (2003b) reported that ammonium combined to make propionate more potent to depress feed intake, and such a situation of high NH3 N and propionate would seem to occur only when N intake was excessive. Although it has been proposed that there is a deamination cost involved with high urea fluxes (Parker et al, 1995), the energetic cost of ureagenesis appears now to be more a consequence of the metabolism of amino acids absorbed in excess of requirements rather than a cost of ammonia absorption and conversion to urea per se (Reynolds, 2003) or possibly only in extremely high availability of ruminal NH3 N (Milano et al, 2000).…”

Section: 2mentioning

confidence: 99%

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Whole-animal nitrogen balance in cattle.

Firkins¹,

Reynolds²

2005

Nitrogen and Phosphorus Nutrition of Cattle: Reducing the Environmental Impact of Cattle Operations

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Effects of lipopolysaccharide exposure on the inflammatory response, butyrate flux, and metabolic function of the ruminal epithelium using an ex vivo model

Kent-Dennis

Penner

2021

Journal of Dairy Science

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Acidotic conditions in the rumen have been associated with compromised barrier function of the ruminal epithelium and translocation of microbe-associated molecular patterns (MAMP) such as lipopolysaccharide (LPS). Interaction of MAMP with the ruminal epithelium may also induce a local proinflammatory response. The aim of this study was to evaluate the potential proinflammatory response of the ruminal epithelium following LPS exposure in Ussing chambers, to investigate whether LPS exposure affects the flux and metabolism of butyrate. Ruminal epithelial tissue from 9 Holstein bull calves were mounted into Ussing chambers and exposed to 0, 10,000, 50,000, or 200,000 endotoxin units (EU)/mL LPS for a duration of 5 h. Radiolabeled 14 C-butyrate (15 mM) was added to the mucosal buffer to assess the mucosal-to-serosal flux of 14 C-butyrate. Additional Ussing chambers, without radioisotope, were exposed to either 0 or 200,000 EU/mL LPS and were used to measure the release of β-hydroxybutyrate (BHB) and IL1B into the buffer, and to collect epithelial tissue for analysis of gene expression. Genes associated with inflammation (TNF, IL1B, CXCL8, PTGS2, TGFB1, TLR2, TLR4), nutrient transport (MCT1, MCT4, SLC5A8, GLUT1), and metabolic function (ACAT1, BDH1, MCU, IGFBP3, IGFBP5) were selected and analyzed using quantitative real-time PCR. Butyrate flux was not significantly affected by LPS exposure; however, we detected a tendency for the mucosal-to-serosal butyrate flux to increase linearly with LPS dose. Bidirectional releases of BHB and IL1B were not affected by LPS exposure. Expression of PTGS2, TGFB1, TLR4, and MCU were downregulated following exposure to LPS ex vivo. We detected no effects on the expression of genes associated with nutrient transport. The results of the present study are interpreted to indicate that, although the inflammatory response of the ruminal epithelium was slightly suppressed, exposure to LPS may have altered metabolic function.

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Chapter 8 Nitrogen metabolism by splanchnic tissues of ruminants

Cited by 4 publications

References 55 publications

Strategies for optimizing nitrogen use by ruminants

Strategies for optimizing nitrogen use by ruminants

Whole-animal nitrogen balance in cattle.

Effects of lipopolysaccharide exposure on the inflammatory response, butyrate flux, and metabolic function of the ruminal epithelium using an ex vivo model

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