Protein metabolism, body composition and oxygen consumption in young bulls divergent in residual feed intake offered two contrasting forage-based diets.

Protein metabolism and body composition have been identified as major determinants of residual feed intake (RFI) in beef cattle fed high-starch fattening diets. This study aimed to evaluate if these two identified RFI determinants in beef cattle are the same across two contrasting silage-based diets. During two consecutive years, an 84-day feed efficiency test (Test A) immediately followed by a second 112-day feed efficiency test (Test B) was carried out using a total of 100 animals offered either one of two diets (either corn silage- or grass silage-based) over 196 days. At the end of Test A, the 32 animals most divergent for RFI (16 extreme RFI animals per diet, eight low RFI and eight high RFI) were identified and evaluated during Test B for their i) N use efficiency (NUE; N retention/N intake) calculated either from a 10-d nitrogen balance trial or from estimations based on body composition changes occurring during the whole experiment (Test A and Test B; 196 days), ii) carcass and whole-body protein turnover rates analysed through the 3-methyl-histidine urinary excretion and the N isotopic turnover rates of urine, respectively, and iii) body composition measured at the slaughterhouse at the end of Test B. Oxygen consumption was measured during Test B for the 100 animals by two GreenFeed systems. Irrespective of the diet, efficient RFI animals tended (P = 0.08) to improve their NUE when N retention was estimated for 196 days or when considering their lower urinary urea-N to total N ratio (P = 0.03). In contrast, NUE calculated during the 10-d N balance showed no differences (P = 0.65) across RFI groups suggesting that this method may not be suitable to capture small NUE differences. Efficient RFI individuals presented higher dressing percentage and muscle deposition in the carcass (P = 0.003) but lighter rumen (P = 0.001), and a trend for lower oxygen consumption (P = 0.08) than inefficient RFI animals irrespective of the diet. Lower protein degradation rates of skeletal muscle and lower protein synthesis rates of plasma proteins were found in efficient RFI cattle but only with the corn silage-based diet (RFI × Diet; P = 0.02). The higher insulinaemia associated with the corn silage-based diet (P = 0.001) seemed to be a key metabolic feature explaining the positive association between protein turnover and RFI only in this diet. Feed N was more efficiently used for growth by efficient RFI animals regardless of the diet but lower protein turnover rates in efficient RFI animals were only observed with corn silage-based diets.

Common and diet-specific metabolic pathways underlying residual feed intake in fattening Charolais yearling bulls.

Residual feed intake (RFI) is one of the preferred traits for feed efficiency animal breeding. However, RFI measurement is expensive and time-consuming and animal ranking may depend on the nature of the diets. We aimed to explore RFI plasma biomarkers and to unravel the underlying metabolic pathways in yearling bulls fed either a corn-silage diet rich in starch (corn diet) or a grass-silage diet rich in fiber (grass diet). Forty-eight extreme RFI animals (Low-RFI, n = 24, versus High-RFI, n = 24, balanced per diet) were selected from a population of 364 Charolais bulls and their plasma was subjected to a targeted LC-MS metabolomic approach together with classical metabolite and hormonal plasma analyses. Greater lean body mass and nitrogen use efficiency, and lower protein turnover were identified as common mechanisms underlying RFI irrespective of the diet. On the other hand, greater adiposity and plasma concentrations of branched-chain amino acids (BCAA) together with lower insulin sensitivity in High-RFI animals were only observed with corn diet. Conversely, greater plasma concentrations of BCAA and total triglycerides, but similar insulin concentrations were noted in efficient RFI cattle with grass diet. Our data suggest that there are diet-specific mechanisms explaining RFI differences in fattening Charolais yearling bulls.

The origin of N isotopic discrimination and its relationship with feed efficiency in fattening yearling bulls is diet-dependent.

Nitrogen (N) isotopic discrimination (i.e. the difference in natural 15N abundance between the animal proteins and the diet; Δ15N) is known to correlate with N use efficiency (NUE) and feed conversion efficiency (FCE) in ruminants. However, results from the literature are not always consistent across studies, likely due to isotopic discrimination pathways that may differ with the nature of diets. The objective of the present study was to assess at which level, from rumen to tissues, Δ15N originates and becomes related to NUE and FCE in fattening yearling bulls when they are fed two contrasted diets. Twenty-four Charolais yearling bulls were randomly divided into two groups and fed during 8 months, from weaning to slaughter, either 1) a high starch diet based on corn silage supplying a balanced N to energy ratio at the rumen level (starch) or 2) a high fiber diet based on grass silage supplying an excess of rumen degradable N (fiber). All animals were slaughtered and samples of different digestive pools (ruminal, duodenal, ileal and fecal contents), animal tissues (duodenum, liver and muscle), blood and urine were collected for each animal. Ruminal content was further used to isolate liquid-associated bacteria (LAB), protozoa and free ammonia, while plasma proteins were obtained from blood. All samples along with feed were analyzed for their N isotopic composition. For both diets, the digestive contribution (i.e. the N isotopic discrimination occurring before absorption) to the Δ15N observed in animal tissues accounted for 65 ± 11%, leaving only one third to the contribution of post-absorptive metabolism. Concerning the Δ15N in digestive pools, the majority of these changes occurred in the rumen (av. Δ15N = 2.12 ± 0.66‰), with only minor 15N enrichments thereafter (av. Δ15N = 2.24 ± 0.41‰), highlighting the key role of the rumen on N isotopic discrimination. A strong, significant overall relationship (n = 24) between Δ15N and FCE or NUE was found when using any post-absorptive metabolic pool (duodenum, liver, or muscle tissues, or plasma proteins; 0.52 < r < 0.73; P ≤ 0.01), probably as these pools reflect both digestive and post-absorptive metabolic phenomena. Fiber diet compared to starch diet had a lower feed efficiency and promoted higher (P ≤ 0.05) Δ15N values across all post-absorptive metabolic pools and some digestive pools (ruminal, duodenal, and ileal contents). The within-diet relationship (n = 12) between Δ15N and feed efficiency was not as strong and consistent as the overall relationship, with contrasted responses between the two diets for specific pools (diet x pool interaction; P ≤ 0.01). Our results highlight the contrasted use of N at the rumen level between the two experimental diets and suggests the need for different equations to predict FCE or NUE from Δ15N according to the type of diet. In conclusion, rumen digestion and associated microbial activity can play an important role on N isotopic discrimination so rumen effect related to diet may interfere with the relationship between Δ15N and feed efficiency in fattening yearling bulls.

Natural 15N abundance in specific amino acids indicates associations between transamination rates and residual feed intake in beef cattle.

Improving the ability of animals to convert feed resources into food for humans is needed for more sustainable livestock systems. Genetic selection for animals eating less while maintaining their performance (i.e., low residual feed intake [RFI]) appears a smart strategy but its effectiveness relies on high-throughput animal phenotyping. Here, we explored plasma nitrogen (N) isotope ratios in an attempt to identify easily superior young bulls in terms of RFI. For this, 48 Charolais young bulls fed two contrasting diets (corn vs. grass silage diets) were selected from a larger population as extreme RFI animals (24 low-RFI vs. 24 high-RFI) and their plasma analyzed for natural 15N abundance (δ15N) in the whole protein (bulk protein) and in the individual protein-bound amino acids (PbAA). For the first time, we showed that the δ 15N in plasma bulk protein differed (P = 0.007) between efficient (low-RFI) and inefficient (high-RFI) cattle regardless of diet. Furthermore, most analyzed PbAA followed the same trend as the bulk protein, with lower (P < 0.05) δ 15N values in more efficient (low-RFI) compared with less efficient (high-RFI) cattle, again regardless of diet. The only three exceptions were Phe, Met, and Lys (P > 0.05) for which the first metabolic reaction before being catabolized does not involve transamination, a pathway known naturally to enrich AAs in 15N. The contrasted isotopic signatures across RFI groups only in those PbAA undergoing transamination are interpreted as differences in transamination rates and N-use efficiency between low- and high-RFI phenotypes. Natural isotopic N signatures in bulk proteins and specific PbAA can be proposed as biomarkers of RFI in growing beef cattle fed different diets. However, the current study cannot delineate whether this effect only occurs post-absorption or to some extent also in the rumen. Our data support the conclusion that most efficient cattle in terms of RFI upregulate N conservation mechanisms compared with less efficient cattle and justify future research on this topic.

Contribution of nutrient fluxes to the evolution of the net energy systems, example of the INRA feeding system for beef cattle.

Energy feeding systems define energy as a whole, but progress made to define metabolizable energy (ME) as the sum of the metabolizable nutrients produced by digestion and available for tissue metabolism in a wide range of nutritional situations opens the way to quantitatively model and predict nutrient fluxes between and within tissues and organs and improve predictions of energy use. This review addresses the contribution of nutrient flux concepts and data to the evolution of the Institut de la Recherche Agronomique (INRA) energy feeding system for growing and fattening cattle and evaluates the outcomes on the net energy (NE) requirements. It summarizes recent progress made to quantitatively predict nutrient fluxes both at digestive and visceral levels. It reviews how nutrient flux concepts and results were introduced in the recently updated INRA feeding system, resulting in improvements in the accuracy of the revised digestible energy (DE) and ME value of diets. The use of an independent database showed that for diets fed to fattening cattle, DE and ME concentrations were downgraded for low-energy-dense diets and upgraded for high-energy-dense diets. We are also showing that compared with its previous version, the updated INRA system improves the quantitative relationship between ME supply and flows of metabolizable nutrients. Evidence is provided on how measured nutrient fluxes at portal level were used to evaluate the predicted flows of metabolizable nutrients. This review then revisits the NE values of diets for fattening cattle as defined by the INRA feeding system and not updated yet. Using an independent database and at similar ME intake, carcass composition was shown to be linearly related to the energy density of diets for fiber-rich diets but not for concentrate-rich diets, suggesting that the efficiency of energy utilization of ME into NE is not linearly related to differences in the composition of the gain. Accounting for the balance of metabolizable nutrients or their proxies in models used to predict carcass composition from ME intake can improve predictions. Overall partitioning aggregated energy fluxes into their subcomponent nutrient fluxes in a more physiological approach offers promising perspectives for the evolution of NE feeding systems.

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 (Δ15Nplasma proteins-diet and Δ13Cplasma 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 Δ15Nplasma 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 (15)N Abundance in Key Amino Acids from Lamb Muscle: Exploring a New Horizon in Diet Authentication and Assessment of Feed Efficiency in Ruminants.

Natural (15)N abundance (δ(15)N) varies between individual amino acids (AAs). We hypothesized that δ(15)N of nontransaminating and essential AAs ("source" AAs, such as phenylalanine) present in animal tissues could be used as a marker of dietary origin, whereas δ(15)N of transaminating AAs ("trophic" AAs, such as glutamic acid) could give more detailed insights into animal feed efficiency. Two diets based on dehydrated Lucerne pellets were tested in growing lambs, which promoted different feed efficiencies. No dietary effects were noted on δ(15)N of any AAs analyzed in lamb muscle. In addition, δ(15)N of phenylalanine was unexpectedly similar to that of glutamic acid, suggesting that δ(15)N of AAs is significantly derived from the metabolism of the rumen microbiota and, thus, are not suited for diet authentication in ruminants. In contrast, the δ(15)N of transaminating AAs facilitates an improved prediction of animal feed efficiency compared to the classical isotopic bulk N analysis.

Conception and development of a bibliographic database of blood nutrient fluxes across organs and tissues in ruminants: data gathering and management prior to meta-analysis.

In the organism, nutrient exchanges among tissues and organs are subject to numerous sources of physiological or nutritional variation, and the contribution of individual factors needs to be quantified before establishing general response laws. To achieve this, meta-analysis of data from publications is a useful tool. The objective of this work was to develop a bibliographic database of nutrient fluxes across organs and tissues of ruminant animals (Flora) under Access using the Merise method. The most important criteria for Flora were the ease to relate the various information, the exhaustivity and the accuracy of the data input, a complete description of the diets, taking into account the methods of the methodological procedures of measurement and analysis of blood nutrients and the traceability of the information. The conceptual data model was built in 6 parts. The first part describes the authors and source of publication, and the person in charge of data input. It clearly separates and identifies the experiments, the groups of animals and the treatments within a publication. The second part is concerned with feeds, diets and their chemical composition and nutritional value. The third and fourth parts describe the infusion of any substrates and the methods employed, respectively. The fifth part is devoted to the results of blood flows and nutrient fluxes. The sixth part gathers miscellaneous experimental information. All these parts are inter-connected. To model this database, the Merise method was utilised and 26 entities and 32 relationships were created. At the physical level, 93 tables were created, corresponding, for the majority, to entities and relationships of the data model. They were divided into reference tables (n = 65) and data tables (n = 28). Data processing was developed in Flora and included the control of the data, generic calculations of unknown data from given data, the automation of the estimation of the missing data or the chemical composition of the diets. It also included the construction of tables for meta-analyses and the study of the variations of several factors within publications (pre-coding of meta-analyses). Overall, the system was built to facilitate the gathering, input, validation, management and retrieval of data from publications.

Influence of maturation and cooking treatments on the nutritional value of bovine meats: Water losses and vitamin B12.

The aim of the study was to determine the influence of maturation and of cooking processes on water losses and on the vitamin B12 content of meat. Three types of muscle (Longissimus lumborum, Longissimus thoracis and Triceps brachii) were sampled from a total of 16 animals, representative of animals raised for meat production in France. Three durations of maturation were compared: 1, 3 and 14 days. Different cooking processes were applied: Longissimus lumborum was deep-fat fried or roasted, Longissimus thoracis was pan fried or grilled and Triceps brachii was braised. The cooking yield averaged 55-56% for Triceps brachii, 73-77% for Longissimus lumborum and 85-87% for Longissimus thoracis. Vitamin B12 concentration in raw meat was significantly higher in Triceps brachii than in Longissimus lumborum and Longissimus thoracis (20.86, 11.53 and 9.21ng/g wet tissue, in the same respective order). When expressed on a wet weight basis, all concentrations were significantly increased by cooking. When expressed on a lipid-free dry basis, significant losses in vitamin B12 were measured only in the braised Triceps brachii (-25%) and in the deep-fat fried Longissimus lumborum (-5.5%) as a result of long duration and high temperature of cooking, respectively. Maturation did not affect the vitamin B12 content of meat, whether raw or cooked.

Nutritional value of meat: the influence of nutrition and physical activity on vitamin B12 concentrations in ruminant tissues.

An important nutritional characteristic of ruminant meat is its high content in vitamin B12. The variability of these contents is not known. Three studies were been set up in order to test the influence of the animal species (2 studies on Charolais steers slaughtered at 30-32 months of age, n = 24 and n = 30 and a third one on lambs slaughtered at 4.5 months of age, n = 21), of the nature of the diet (grass vs. maize silage, lucerne or concentrate diets) and of physical activity (without or with walking) on the vitamin B12 contents of different muscle types (rather oxidative (Rectus Abdominis, RA), intermediate (Longissimus Dorsi, LD), or glycolytic (Semi Tendinosus, ST)) and on the liver. The animals were supplemented in macro and trace minerals according to usual feeding practices in France in order to theoretically avoid any risk of deficiency. For this reason, cobalt allowances, which are necessary for the ruminal synthesis of vitamin B12, could differ among treatments. The results indicate the following: (1) cobalt allowances varied widely among treatments, from (sub-)deficient to plethoric allowances, influencing vitamin B12 contents of the liver, and muscles (only in case of deficiency), (2) the effects of dietary treatments or of physical exercise were essentially related to differences in cobalt allowances, (3) the oxidative type muscle (RA) showed contents which were double those in glycolytic type muscle (RA 10.8 vs. ST 5.0 ng.g(-1)) and (4) vitamin B12 contents of raw muscles were lower than the values indicated in tables of feed composition for humans for cooked meat (0.5 to 1 vs. 2 to 3 microg.100 g(-1)).

Effects of intraruminal propionate supplementation on nitrogen utilisation by the portal-drained viscera, the liver and the hindlimb in lambs fed frozen rye grass.

The influence of propionate supplementation on the splanchnic metabolism of amino acids (AA) and other N compounds (urea-N and NH3-N) and the supply of AA and NH3-N to the hindlimb was investigated in growing lambs. Six rumen-cannulated and multicatheterised lambs (32.2 kg) were fed frozen rye grass at 690 kJ metabolisable energy intake/d per kg average metabolic body weight. They were infused intraruminally with a salt solution (control) or with propionate solutions at 0.23 mol/l (P1) or 0.41 mol/l (P2) infused at a maximal rate of 1.68 (SD 0.057) ml/min according to a repeated Latin square design. The propionate infusion did not increase the net portal appearance of total AA (TAA)-N but increased that of some branched-chain AA (valine and to a lesser extent isoleucine). Simultaneously, the propionate treatment (especially P2) induced an increased TAA utilisation by the liver. This was due mainly to an increased (+79%; P<0.07) utilisation of the essential AA and particularly the branched-chain AA. A stimulation of protein synthesis in the liver is hypothesised since (1) propionate stimulated insulin secretion and (2) utilisation of non-essential AA were less influenced by the propionate treatment in the liver (except for alanine), suggesting that the AA utilised by the liver were directed towards protein synthesis rather than towards oxidation or urea synthesis. At the splanchnic level, the propionate treatment did not have any effect on the TAA, non-essential AA and essential AA, except for a net splanchnic release that was decreased for leucine (P<0.02) and methionine (P<0.01) and increased for threonine (P<0.05). The propionate treatment did not have any effect on the hindlimb uptake of AA (essential and non-essential). As a consequence, even though the propionate treatment induced some major alterations in the splanchnic metabolism of AA, there were no changes in the net AA balance in the hindlimb (and hence probably on muscle growth). The role of the splanchnic tissues in the regulation of the AA supply to the peripheral tissues (such as muscle) therefore appears to be prominent in the regulation of muscle growth. Whether the peripheral tissues regulate their own supply by interacting with the splanchnic tissues (and especially the liver) or the liver is the only regulator of the AA supply to the muscle remains in doubt.

The incorporation of solubilized wheat proteins in milk replacers for veal calves: effects on growth performance and muscle oxidative capacity.

Replacement of skim milk proteins by solubilized wheat protein (SWP) in milk replacers for veal calves would contribute to the reduction in feeding costs. The occurrence of metabolic disorders has, however, been reported. Forty-two male calves received one of three treatments over 140 days: a control diet, a diet containing SWP without or with branched-chain amino acid supplementation. Liveweight gain, carcass yield, color and conformation did not show any significant differences. No metabolic disorders were noted. Supplementation with branched-chain amino acids reduced the marginal Val deficiency but did not modify the growth performances. With the SWP containing diets, the plasma metabolite profile was characteristic of those observed with non-clotting diets. It was statistically correlated to the changes in the orientation of the Semitendinosus muscle energy metabolism towards a more oxidative type and to indications of a lower efficiency of amino acid utilisation for protein deposition. At the present levels of inclusion, SWP proved to be an interesting alternative to the sole use of whey as the protein source in milk replacers for veal calves.

Intraruminal propionate supplementation modifies hindlimb energy metabolism without changing the splanchnic release of glucose in growing lambs.

The influence of propionate supplementation on the splanchnic metabolism of energy-yielding nutrients and the supply of glucose to the hindlimb was investigated in growing lambs. Six rumen-cannulated and multicatheterized lambs (32.2 kg), fed frozen rye grass at 690 kJ metabolizable energy intake/d per kg body weight0.75, were infused intraruminally with a salt solution (control) or with propionate solutions at 0.55 mol/d (P1) or 0.98 mol/d (P2) according to a replicated Latin square design. In the rumen fluid, supplementation decreased the acetate:propionate molar ratio from 2.36:1 to 1.37:1, without modifying the ruminal concentrations of acetate and NH4. As a result, the portal appearance of propionate increased by 51 and 72 % with P1 and P2, respectively, and that of l-lactate doubled. Across the liver, net extraction of propionate increased by 47 and 67 % with P1 and P2, respectively. However, the net hepatic production of glucose remained unchanged, probably as the result of a substantial rise in insulin secretion and its hepatic extraction. Overall, the net splanchnic release of acetate, glucose and butyrate was not modified while that of l-lactate increased. Despite this, the net uptake of acetate, glucose, l-lactate and non-esterified fatty acids by the hindlimb increased. Propionate probably enhanced the storage of energy-yielding nutrients in the hindlimb, despite their unchanged release by the splanchnic tissues and the unmodified insulinaemia. Regulatory mechanisms are not clear.

Propionate supplementation did not increase whole body glucose turnover in growing lambs fed rye grass.

The objective of the present study was to investigate the effects of propionate supplementation on whole body glucose turnover in growing lambs fed frozen rye-grass at 1.5 x maintenance using [1-13C]-glucose. Intraruminal infusion of propionate (0.55 and 0.91 mol x d(-1)) increased the ruminal molar proportions of propionate from 25% with the control to 40% with the highest propionate treatment. It did not however modify glucose turnover (26 mmol x d(-1) x kg(-1)), nor the conversion of its carbon into L-lactate (21%) and alanine (21%), nor glucose recycling (9%). All of the results suggest that in the present conditions glucose turnover and metabolism were not influenced by the supply of propionate.

Whole body glucose turnover in growing and non-productive adult ruminants: meta-analysis and review.

The objectives of the present paper were to review and quantitatively determine the influence of the nutritional factors on whole body glucose turnover in growing and adult non-productive ruminants. A meta-analysis approach was used. The dietary grain: forage ratio significantly increased the slope of the relationship between glucose turnover and metabolisable energy intake. This effect was probably associated with the inclusion of maize rather than any other grain source in the diet. The analysis pointed out the possible differences in response between growing and adult non-productive animals, and suggested that the performance level of the animals (and their glucose requirements) could contribute to regulating whole body glucose turnover. This aspect would warrant further investigation.