Natural (15)N Abundance in Key Amino Acids from Lamb Muscle: Exploring a New Horizon in Diet Authentication and Assessment of Feed Efficiency in Ruminants

Assessing short-term feed efficiency and its association with biological markers in herbage-fed dairy cows

Feed efficiency is an important trait of dairy production. However, assessing feed efficiency is constrained by the associated cost and difficulty in measuring individual feed intake, especially on pastures. The objective of this study was to investigate short-term feed efficiency traits of herbage-fed dairy cows and screening of potential biomarkers (n = 238). Derived feed efficiency traits were ratio-based (i.e., feed conversion ratio (FCR) and N use efficiency (NUE)) or residual-based (i.e., residual feed intake (RFI), residual energy intake (REI), and residual N intake (RNI)). Thirty-eight Holstein and 16 Swiss Fleckvieh dairy cows underwent a 7-d measurement period during mid- and/or late-lactation. The experimental data (n = 100 measurement points) covered different lactational and herbage-fed system situations: mid-lactation grazing (n = 56), late-lactation grazing (n = 28), and late-lactation barn feeding (n = 16). During each measuring period, the individual herbage intake of each cow was estimated using the n-alkane marker technique. For each cow, biomarkers representing milk constituents (n = 109), animal characteristics (n = 13), behaviour, and activity (n = 46), breath emissions (n = 3), blood constituents (n = 35), surface, and rectal temperature (n = 29), hair cortisol (n = 1), and near-infrared (NIR) spectra of faeces and milk (n = 2) were obtained. The relationships between biomarkers and efficiency traits were statistically analysed with univariate linear regression and for NIR spectra using partial least squares regression with feed efficiency traits. The feed efficiency traits were interrelated with each other (r: -0.57 to -0.86 and 0.49-0.81). The biomarkers showed varying R2 values in explaining the variability of feed efficiency traits (FCR: 0.00-0.66, NUE: 0.00-0.74, RFI: 0.00-0.56, REI: 0.00-0.69, RNI: 0.00-0.89). Overall, the feed efficiency traits were best explained by NIR spectral characteristics of milk and faeces (R2: 0.25-0.89). Biomarkers show potential for predicting feed efficiency in herbage-fed dairy cows. NIR spectra data analysis of milk and faeces presents a promising method for estimating individual feed efficiency upon further validation of prediction models. Future applications will depend on the ability to improve the robustness of biomarkers to predict feed efficiency in a greater variety of environments (locations), managing conditions, feeding systems, production intensities, and other aspects.

Isotopes Don't Lie, differentiating organic from conventional banana (Musa AAA, Cavendish subgroup) fruits using C and N stable isotopes

With the dramatic increase of organic banana production worldwide, it is essential to be able to monitor compliance with organic specifications. While the detection of pesticide fraud is routinely controlled by detecting pesticide residues in organic bananas, the detection of fertilizer fraud is much more complex. We compared the δ¹³C and δ¹⁵N isotopic values of green bananas from organic and conventional farms at seven sites around the world. In our whole dataset, the δ¹⁵N values of banana fruits ranged between -1.25 and + 8.91‰. In all sites, δ¹⁵N values of organic banana were significantly higher than conventional fruits (mean value of + 5.24‰ and + 2.342‰, respectively). Conversely, the type of fertilization did not significantly alter δ¹³C values. Our results suggest that it is possible, upon arrival in importing countries, to differentiate bananas grown with synthetic fertilizer from those grown with organic fertilizer.

Compound-Specific 14N/15N Analysis of Amino Acid Trimethylsilylated Derivatives from Plant Seed Proteins

Isotopic analyses of plant samples are now of considerable importance for food certification and plant physiology. In fact, the natural nitrogen isotope composition (δ¹⁵N) is extremely useful to examine metabolic pathways of N nutrition involving isotope fractionations. However, δ¹⁵N analysis of amino acids is not straightforward and involves specific derivatization procedures to yield volatile derivatives that can be analysed by gas chromatography coupled to isotope ratio mass spectrometry (GC-C-IRMS). Derivatizations other than trimethylsilylation are commonly used since they are believed to be more reliable and accurate. Their major drawback is that they are not associated with metabolite databases allowing identification of derivatives and by-products. Here, we revisit the potential of trimethylsilylated derivatives via concurrent analysis of δ¹⁵N and exact mass GC-MS of plant seed protein samples, allowing facile identification of derivatives using a database used for metabolomics. When multiple silylated derivatives of several amino acids are accounted for, there is a good agreement between theoretical and observed N mole fractions, and δ¹⁵N values are satisfactory, with little fractionation during derivatization. Overall, this technique may be suitable for compound-specific δ¹⁵N analysis, with pros and cons.

Exploring the Intestinal Microbiota and Metabolome Profiles Associated With Feed Efficiency in Pacific Abalone (Haliotis discus hannai)

Feed efficiency (FE) is critical to the economic and environmental benefits of aquaculture. Both the intestines and intestinal microbiota play a key role in energy acquisition and influence FE. In the current research, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between abalones with high [Residual feed intake (RFI) = -0.029] and low FE (RFI = 0.022). The FE of group A were significantly higher than these of group B. There were significant differences in intestinal microbiota structures between high- and low-FE groups, while higher microbiota diversity was observed in the high-FE group. Differences in FE were also strongly correlated to variations in intestinal digestive enzyme activity that may be caused by Pseudoalteromonas and Cobetia. In addition, Saprospira, Rhodanobacteraceae, Llumatobacteraceae, and Gaiellales may potentially be utilized as biomarkers to distinguish high- from low-FE abalones. Significantly different microorganisms (uncultured beta proteobacterium, BD1_7_clade, and Lautropia) were found to be highly correlated to significantly different metabolites [DL-methionine sulfoxide Arg-Gln, L-pyroglutamic acid, dopamine, tyramine, phosphatidyl cholines (PC) (16:0/16:0), and indoleacetic acid] in the high- and low-FE groups, and intestinal trypsin activity also significantly differed between the two groups. We propose that interactions occur among intestinal microbiota, intestinal metabolites, and enzyme activity, which improve abalone FE by enhancing amino acid metabolism, immune response, and signal transduction pathways. The present study not only elucidates mechanisms of variations in abalone FE, but it also provides important basic knowledge for improving abalone FE by modulating intestinal microbiota.

Effects of pretreatment with reducing sugars or an enzymatic cocktail before extrusion of fava bean on nitrogen metabolism and performance of dairy cows

The aim of this study was to determine the effects of pretreatment with reducing sugars or with an enzymatic cocktail before extrusion of fava bean on intake, milk yield and composition, N partitioning, and plasma and ruminal parameters. The main hypothesis was that these pretreatment conditions would allow better N protection in the rumen compared with classic pretreatment before extrusion, thanks to an increase of sugar proportion, either exogenous or endogenous with enzymatic actions. Sixteen Holstein cows were used in a 4 × 4 Latin square design experiment. Cow were fed a diet with a 56:44 forage to concentrate ratio and containing 16.2% of crude protein (CP; dry matter basis). Concentrate consisted of fava bean:linseed blends (90:10%, raw basis) distributed either raw, extruded after pretreatment without additive, extruded after pretreatment with reducing sugars, or extruded after pretreatment with an enzymatic cocktail. The experimental blends provided 53% of total CP in the diet. Intake, milk yield and composition, ruminal pH, volatile fatty acids and ammonia kinetics, apparent total-tract nutrient digestibilities and N partitioning, Maillard compounds in feed and feces, plasma AA, and ¹⁵N natural enrichment were measured. Data were analyzed using analysis of variance according to the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). Extrusion without additive during pretreatment led to higher contents of Maillard compounds in the blend, a lower enzymatic CP degradability, a numerically lower ammonia content in ruminal fluid, and a trend of higher plasma EAA concentration, all suggesting a decrease in degradability of proteins in the rumen, and a subsequent increase in metabolizable protein supply. Compared with pretreatment without additive, adding reducing sugars or an enzymatic cocktail during pretreatment led to an increase in Maillard compound contents in the extruded blends, and to an increase (+50 mg/L) in rumen ammonia content. With reducing sugars, digestibility of Nɛ-carboxymethyl-lysine was numerically lower, and plasma EAA concentration tended to decrease, suggesting an overprotection of proteins in the intestine. With the enzymatic cocktail, plasma EAA concentration was similar than without additive during pretreatment, suggesting a similar metabolizable protein supply with both treatments. Finally, no change in N partitioning between milk, urine, and feces was observed whatever the diet.

Nitrogen partitioning and isotopic discrimination are affected by age and dietary protein content in growing lambs

It is difficult to separate an age-dependent fall in nitrogen use efficiency (NUE; N balance/N intake) in growing ruminants from a progressively decrease in animal protein requirements over time. This study examined the effect of dietary protein content on N partitioning, digestibility and N isotopic discrimination between the animal and its diet (Δ15Nanimal-diet) evaluated at two different fattening periods (early v. late). Twenty-four male Romane lambs (age: 19 ± 4.0 days; BW: 8.3 ± 1.39 kg) were equally allocated to three dietary CP treatments (15%, 17% and 20% CP on a DM basis). Lambs were reared with their mothers until weaning, thereafter housed in individual pens until slaughter (45 kg BW). During the post-weaning period, lambs were allocated twice (early fattening (30 days post-weaning) and late fattening (60 days post-weaning)) to metabolic cages for digestibility and N balance study. When diet CP content increased, the average daily gain of lambs increased (P < 0.05) while the age at slaughter decreased (P = 0.01), but no effect was observed on feed efficiency (P > 0.10). Diet CP content had limited effect on lamb carcass traits. Higher fibre digestibility was observed at the early v. late fattening period (P < 0.001). The N intake and the urinary N excretion increased when diet CP content increased (P < 0.001) and when shifting from early to late fattening period (P < 0.001). Faecal N excretion (P = 0.14) and N balance (P > 0.10) were not affected by diet CP content. Nitrogen digestibility increased (P < 0.001) as the diet CP content increased and on average it was greater at late v. early fattening period (P = 0.02). The NUE decreased (P = 0.001) as the diet CP content increased and as the lamb became older (P < 0.001). However, the age-dependent fall in NUE observed was lower at high v. low dietary CP content (CP × age interaction; P = 0.04). The Δ15Nanimal-diet was positively correlated (P < 0.05) with N intake (r = 0.59), excretion of faecal N (r = 0.41), urinary N (r = 0.69) and total manure N (r = 0.64), while negatively correlated with NUE (r = -0.57). Overall, the experiment showed NUE was lower in older lambs and when lambs were fed high diet CP content, and that Δ15Nanimal-diet was a useful indicator not only for NUE but also for urinary N excretion, which is a major environmental pollution factor on farm.

Fat accretion measurements strengthen the relationship between feed conversion efficiency and Nitrogen isotopic discrimination while rumen microbial genes contribute little

The use of biomarkers for feed conversion efficiency (FCE), such as Nitrogen isotopic discrimination (Δ15N), facilitates easier measurement and may be useful in breeding strategies. However, we need to better understand the relationship between FCE and Δ15N, particularly the effects of differences in the composition of liveweight gain and rumen N metabolism. Alongside measurements of FCE and Δ15N, we estimated changes in body composition and used dietary treatments with and without nitrates, and rumen metagenomics to explore these effects. Nitrate fed steers had reduced FCE and higher Δ15N in plasma compared to steers offered non-nitrate containing diets. The negative relationship between FCE and Δ15N was strengthened with the inclusion of fat depth change at the 3rd lumbar vertebrae, but not with average daily gain. We identified 1,700 microbial genes with a relative abundance >0.01% of which, 26 were associated with Δ15N. These genes explained 69% of variation in Δ15N and showed clustering in two distinct functional networks. However, there was no clear relationship between their relative abundances and Δ15N, suggesting that rumen microbial genes contribute little to Δ15N. Conversely, we show that changes in the composition of gain (fat accretion) provide additional strength to the relationship between FCE and Δ15N.

Exploration of Biological Markers of Feed Efficiency in Young Bulls

The efficiency with which ruminants convert feed to desirable products is difficult to measure under normal commercial settings. We explored the use of potential biological markers from easily obtainable samples, that is, blood, hair, and feces, to characterize potential causes of divergent efficiency when considered as residual feed intake (RFI) or feed conversion efficiency (FCE). A total of 54 Charolais bulls, 20 in period 1 and 34 in period 2, were examined for individual dry matter intake (DMI) and growth. Bulls were offered a diet of 70:30 wrapped grass silage to concentrate for 99 d. At the conclusion of the test period, blood samples were collected for the determination of vitamins B₂ and B₆, and plasma used for the determination of metabolites, natural isotopic ¹⁵N abundance (¹⁵N NIA, expressed as δ¹⁵N ‰) and fractionation (Δ¹⁵N_{plasma proteins-diet} and Δ¹³C_{plasma proteins-diet}) and near-infrared spectroscopy (NIRS). Feces were analyzed by NIRS. Bulls were slaughtered at 15-17 months of age and carcass characteristics determined. Bulls were ranked according to RFI with extremes (SD ± 0.5; n = 31) classified as either efficient (Neg-RFI) or inefficient (Pos-RFI). Extreme bulls were then classified for FCE (high vs low FCE), changing the groups. Pos-RFI bulls consumed 14% more feed than Neg-RFI bulls for the same level of weight gain. Low FCE bulls tended to eat more, but had lower weight gains than high FCE bulls. No differences were detected in carcass conformation, fat scores, hot carcass weight, or dressing percentage. Yet, heart and bladder weights were heavier in Pos-RFI, and rumen weight tended to be heavier in Pos-RFI bulls. RFI did not affect bulk ¹⁵N or ¹³C fractionation. A negative correlation was observed between FCE and Δ¹⁵N_{plasma proteins-diet}. Inefficient bulls (Pos-RFI) had higher δ¹⁵N in glycine compared to Neg-RFI bulls. Similarly, metabolomic analysis showed a tendency for concentrations of glycine and sarcosine to be elevated in Pos-RFI bulls, whereas aspartic acid and carnosine tended to be elevated, and serine tended to be lower in High FCE. Among vitamins, only flavin adenine dinucleotide concentration was higher in the blood of bulls with High FCE. These results suggest that the two feed efficiency metrics differ in the underlying mechanisms of metabolism, where RFI is driven by differences in the energetic requirements of visceral organs and the extent of AA catabolism.

Natural Isotope Abundance in Metabolites: Techniques and Kinetic Isotope Effect Measurement in Plant, Animal, and Human Tissues

The natural isotope abundance in bulk organic matter or tissues is not a sufficient base to investigate physiological properties, biosynthetic mechanisms, and nutrition sources of biological systems. In fact, isotope effects in metabolism lead to a heterogeneous distribution of ²H, ¹⁸O, ¹³C, and ¹⁵N isotopes in metabolites. Therefore, compound-specific isotopic analysis (CSIA) is crucial to biological and medical applications of stable isotopes. Here, we review methods to implement CSIA for ¹⁵N and ¹³C from plant, animal, and human samples and discuss technical solutions that have been used for the conversion to CO₂ and N₂ for IRMS analysis, derivatization and isotope effect measurements. It appears that despite the flexibility of instruments used for CSIA, there is no universal method simply because the chemical nature of metabolites of interest varies considerably. Also, CSIA methods are often limited by isotope effects in sample preparation or the addition of atoms from the derivatizing reagents, and this implies that corrections must be made to calculate a proper δ-value. Therefore, CSIA has an enormous potential for biomedical applications, but its utilization requires precautions for its successful application.

'Trophic' and 'source' amino acids in trophic estimation: a likely metabolic explanation

Amino acid nitrogen isotopic analysis is a relatively new method for estimating trophic position. It uses the isotopic difference between an individual's 'trophic' and 'source' amino acids to determine its trophic position. So far, there is no accepted explanation for the mechanism by which the isotopic signals in 'trophic' and 'source' amino acids arise. Yet without a metabolic understanding, the utility of nitrogen isotopic analyses as a method for probing trophic relations, at either bulk tissue or amino acid level, is limited. I draw on isotopic tracer studies of protein metabolism, together with a consideration of amino acid metabolic pathways, to suggest that the 'trophic'/'source' groupings have a fundamental metabolic origin, to do with the cycling of amino-nitrogen between amino acids. 'Trophic' amino acids are those whose amino-nitrogens are interchangeable, part of a metabolic amino-nitrogen pool, and 'source' amino acids are those whose amino-nitrogens are not interchangeable with the metabolic pool. Nitrogen isotopic values of 'trophic' amino acids will reflect an averaged isotopic signal of all such dietary amino acids, offset by the integrated effect of isotopic fractionation from nitrogen cycling, and modulated by metabolic and physiological effects. Isotopic values of 'source' amino acids will be more closely linked to those of equivalent dietary amino acids, but also modulated by metabolism and physiology. The complexity of nitrogen cycling suggests that a single identifiable value for 'trophic discrimination factors' is unlikely to exist. Greater consideration of physiology and metabolism should help in better understanding observed patterns in nitrogen isotopic values.