Nitrogen isotopic discrimination as a biomarker of between-cow variation in the efficiency of nitrogen utilization for milk production: A meta-analysis.

Estimating the efficiency of N utilization for milk production (MNE) of individual cows at a large scale is difficult, particularly because of the cost of measuring feed intake. Nitrogen isotopic discrimination (Δ15N) between the animal (milk, plasma, or tissues) and its diet has been proposed as a biomarker of the efficiency of N utilization in a range of production systems and ruminant species. The aim of this study was to assess the ability of Δ15N to predict the between-animal variability in MNE in dairy cows using an extensive database. For this, 20 independent experiments conducted as either changeover (n = 14) or continuous (n = 6) trials were available and comprised an initial data set of 1,300 observations. Between-animal variability was defined as the variation observed among cows sharing the same contemporary group (CG; individuals from the same experimental site, sampling period, and dietary treatment). Milk N efficiency was calculated as the ratio between mean milk N (grams of N in milk per day) and mean N intake (grams of N intake per day) obtained from each sampling period, which lasted 9.0 ± 9.9 d (mean ± SD). Samples of milk (n = 604) or plasma (n = 696) and feeds (74 dietary treatments) were analyzed for natural 15N abundance (δ15N), and then the N isotopic discrimination between the animal and the dietary treatment was calculated (Δ15n = δ15Nanimal - δ15Ndiet). Data were analyzed through mixed-effect regression models considering the experiment, sampling period, and dietary treatment as random effects. In addition, repeatability estimates were calculated for each experiment to test the hypothesis of improved predictions when MNE and Δ15N measurements errors were lower. The considerable protein mobilization in early lactation artificially increased both MNE and Δ15N, leading to a positive rather than negative relationship, and this limited the implementation of this biomarker in early lactating cows. When the experimental errors of Δ15N and MNE decreased in a particular experiment (i.e., higher repeatability values), we observed a greater ability of Δ15N to predict MNE at the individual level. The predominant negative and significant correlation between Δ15N and MNE in mid- and late lactation demonstrated that on average Δ15N reflects MNE variations both across dietary treatments and between animals. The root mean squared prediction error as a percentage of average observed value was 6.8%, indicating that the model only allowed differentiation between 2 cows in terms of MNE within a CG if they differed by at least 0.112 g/g of MNE (95% confidence level), and this could represent a limitation in predicting MNE at the individual level. However, the one-way ANOVA performed to test the ability of Δ15N to differentiate within-CG the top 25% from the lowest 25% individuals in terms of MNE was significant, indicating that it is possible to distinguish extreme animals in terms of MNE from their N isotopic signature, which could be useful to group animals for precision feeding.

Methionine-balanced diets improve cattle performance in fattening young bulls fed high-forage diets through changes in nitrogen metabolism.

Ruminants fed high-forage diets usually have a low feed efficiency, and their performances might be limited by methionine (Met) supply. However, the INRA feeding system for growing cattle does not give recommendation for this amino acid (AA). This study aimed to assess the effects of Met-balanced diets on animal performance and N metabolism in young bulls fed high-forage diets formulated at or above protein requirements. Four diets resulting from a factorial arrangement of two protein levels (Normal (13·5 % crude protein) v. High (16·2 % crude protein)) crossed with two Met concentrations (unbalanced (2·0 % of metabolisable protein) v. balanced (2·6 % of metabolisable protein)) were tested on thirty-four fattening Charolais bulls for 7 months before slaughter. Animal growth rate was greater in Met-balanced diets (+8 %; P = 0·02) with a trend for a greater impact in High v. Normal protein diets (P = 0·10). This trend was observed in lower plasma concentrations of branched-chain AA only when Met supplementation was applied to the Normal protein diet (P ≤ 0·06) suggesting another co-limiting AA at Normal protein level. Feed conversion efficiency and N use efficiency were unaffected by Met supplementation (P > 0·05). However, some plasma indicators suggested a better use of AA when High protein diets were balanced v. unbalanced in Met. The proportion of total adipose tissue in carcass increased (+5 percent units; P = 0·03), whereas that of muscle decreased on average 0·8 percent units (P = 0·05) in Met-balanced diets. Our results justify the integration of AA into dietary recommendations for growing cattle.

Net hepatic release of glucose from precursor supply in ruminants: a meta-analysis.

For their glucose supply, ruminants are highly dependent on the endogenous synthesis in the liver, but despite the numerous studies that evaluated hepatic glucose production, very few simultaneously measured hepatic glucose production and uptake of all precursors. As a result, the variability of precursor conversion into glucose in the liver is not known. The present study aimed at investigating by meta-analysis the relationships between hepatic glucose net release and uptake of precursors. We used the FLuxes of nutrients across Organs and tissues in Ruminant Animals database, which gathers international results on net nutrient fluxes at splanchnic level measured in catheterized animals. Response equations were developed for intakes up to 41 g DM intake/kg BW per day of diets varying from 0 to 100 g of concentrate/100 g DM in the absence of additives. The net hepatic uptake of propionate, α-amino-N and l-lactate was linearly and better related to their net portal appearance (NPA) than to their afferent hepatic flux. Blood flow data were corrected for lack of deacetylation of the para-aminohippuric acid, and this correction was shown to impact the response equations. To develop response equations between the availability of precursors (portal appearance and hepatic uptake) and net glucose hepatic release, missing data on precursor fluxes were predicted from dietary characteristics using previously developed response equations. Net hepatic release of glucose was curvilinearly related to hepatic supply and uptake of the sum of precursors, suggesting a lower conversion rate of precursors at high precursor supply. Factors of variation were explored for the linear portion of this relationship, which applied to NPA of precursors ranging from 0.99 to 9.60 mmol C/kg BW per h. Hepatic release of glucose was shown to be reduced by the portal absorption of glucose from diets containing bypass starch and to be increased by an increased uptake of ß-hydroxybutyrate indicative of higher body tissue mobilization. These relationships were affected by the physiological status of the animals. In conclusion, we established equations that quantify the net release of glucose by the liver from the net availability of precursors. They provide a quantitative overview of factors regulating hepatic glucose synthesis in ruminants. These equations can be linked with the predictions of portal absorption of nutrients from intake and dietary characteristics, and provide indications of glucose synthesis from dietary characteristics.

Postruminal infusions of amino acids or glucose affect metabolisms of splanchnic, mammary, and other peripheral tissues and drive amino acid use in dairy cows.

Effects of AA and glucose infusions on efficiency of use of essential AA (EAA) were studied according to a 2 × 2 factorial using 5 multicatheterized cows in a 4 × 4 Latin square plus one cow, with 2-wk periods. The diet provided 87% of energy and 70% of metabolizable protein requirements, and the 4 treatments were abomasal infusions of (1) water, (2) an AA mixture with a casein profile (695 g/d), (3) glucose (1,454 g/d), or (4) a combination of AA and glucose infusions. Milk samples were collected on the last 6 milkings. On d 14, 6 blood samples were collected from arterial, and portal, hepatic, and mammary venous vessels. Splanchnic plasma flow was calculated by dilution of p-aminohippurate and mammary flow by the Fick principle using Phe + Tyr. The net flux of AA across tissues [splanchnic, i.e., portal-drained viscera (PDV) + liver, and mammary gland] was calculated as the efflux minus the influx across that tissue. The efficiency of EAA was calculated as the sum of exported true proteins [milk protein yield (MPY), scurf, and metabolic fecal protein] multiplied by their respective AA profile and divided by the predicted AA supply minus AA endogenous urinary loss. In addition, catabolism was estimated for each tissue: AA supply - (portal net flux + metabolic fecal protein) for the PDV; -hepatic net flux for the liver; splanchnic net flux - (-mammary net flux + scurf) for the other peripheral tissues; and -mammary net flux - milk for the mammary gland. The MIXED procedure (SAS Institute Inc., Cary, NC) was used with cow as a random effect. No AA × glucose interaction existed for most of the measured parameters. With infusions of AA and glucose, MPY increased by 17 and 14%, respectively. The decreased efficiency of EAA-N with AA infusion resulted from increased EAA-N in MPY smaller than the increased EAA-N supply and was accompanied by increased liver catabolism of His + Met + Phe (representing group 1 AA) and increased mammary and PDV catabolisms of group 2 AA-N (Ile, Leu, Lys, and Val). In contrast, the increased efficiency of EAA-N with glucose infusion, resulting from increased EAA-N in MPY with no change in EAA-N supply, was accompanied by decreased mammary catabolism of group 2 AA-N and hepatic catabolism of His + Met + Phe. No mammary catabolism of His, Met, and Phe existed in all treatments, as indicated by the mammary uptake to milk output ratio close to one for these EAA. Therefore, the mammary gland contributes significantly to variations of efficiency of group 2 AA-N through variations of AA catabolism, in response to both AA and glucose supplies, whereas additional PDV catabolism was observed with increased AA supply. Partition of AA use between tissues allows to delineate their anabolic or catabolic fate across tissues and better understand changes of efficiency of EAA in response to protein and energy supplies.

Amino acid efficiencies of utilization vary by different mechanisms in response to energy and protein supplies in dairy cows: Study at mammary-gland and whole-body levels.

Variations of mammary gland (MG) metabolism were studied in dairy cows in response to diets containing 2 levels of net energy of lactation [NEL; 25.0 and 32.5 Mcal/d for low (LE) and high energy (HE), respectively], combined with 2 levels of metabolizable protein [MP, 1,266 and 2,254 g/d of protein digestible in the intestine for low (LP) and high protein (HP), respectively] in a 2 × 2 factorial arrangement. Four cows received 4 diets (LELP, HELP, LEHP, and HEHP) in a 4 × 4 Latin square design with 2-wk experimental periods. Milk production and feed intake were measured on the last 5 d of each period, whereas MG net uptake of AA was determined on d 13. Efficiencies were estimated as the sum of measured milk true protein yield (MPY) and of estimations of metabolic fecal and scurf proteins multiplied by their respective AA profile and divided by the estimated AA supply minus the AA endogenous urinary loss. The increased MPY in the HE compared with the LE diets (higher by 123 g/d) was accompanied by increased mammary plasma flow and MG uptake of the nonessential AA (NEAA) and the essential AA (EAA), except for branched-chain AA. In contrast, the increase in MPY (higher by 104 g/d) observed in the HP compared with the LP diets was linked to increased MG uptake of EAA without a change in mammary plasma flow and a decreased NEAA uptake. Because MG uptake of total AA-N was almost equal to cows' milk output on a nitrogen basis, these different mechanisms involve a large MG flexibility, with variable synthesis of NEAA. In addition, MP efficiency did not increase only through increased MPY in the HE compared with the LE diets but also through metabolic fecal protein, estimated to increase (by 65 g/d) with dry matter intake. The MPY increased in the HP compared with the LP diets, but the increase was smaller than the calculated increase (greater by 993 g/d) in MP supply. The highest MG clearance rates of individual EAA could suggest that Met, His, and Lys were limiting in LP, and Met was the most limiting AA in HP. Interestingly, a similar hypothesis could be stated by analyzing estimated AA efficiencies. The highest efficiencies among EAA, observed for His in HELP and for Met with the other diets, could indicate that they were the most limiting AA in these respective diets, whereas other EAA (including Lys) efficiencies varied with MP efficiency. The MG metabolic flexibility with regard to individual AA utilization partially contributes to the anabolic fate of AA through MPY; however, other export proteins also contribute to variations in MP and AA efficiencies.

Empirical prediction of net splanchnic release of ketogenic nutrients, acetate, butyrate and ß-hydroxybutyrate in ruminants: a meta-analysis.

For energy feeding systems for ruminants to evolve towards a nutrient-based system, dietary energy supply has to be determined in terms of amount and nature of nutrients. The objective of this study was to establish response equations of the net hepatic flux and net splanchnic release of acetate, butyrate and ß-hydroxybutyrate to changes in diet and animal profiles. A meta-analysis was applied on published data compiled from the FLuxes of nutrients across Organs and tissues in Ruminant Animals database, which pools the results from international publications on net splanchnic nutrient fluxes measured in multi-catheterized ruminants. Prediction variables were identified from current knowledge on digestion, hepatic and other tissue metabolism. Subsequently, physiological and other, more integrative, predictors were obtained. Models were established for intakes up to 41 g dry matter per kg BW per day and diets containing up to 70 g concentrate per 100 g dry matter. Models predicted the net hepatic fluxes or net splanchnic release of each nutrient from its net portal appearance and the animal profile. Corrections were applied to account for incomplete hepatic recovery of the blood flow marker, para-aminohippuric acid. Changes in net splanchnic release (mmol/kg BW per hour) could then be predicted by combining the previously published net portal appearance models and the present net hepatic fluxes models. The net splanchnic release of acetate and butyrate were thus predicted from the intake of ruminally fermented organic matter (RfOM) and the nature of RfOM (acetate: residual mean square error (RMSE)=0.18; butyrate: RMSE=0.01). The net splanchnic release of ß-hydroxybutyrate was predicted from RfOM intake and the energy balance of the animals (RMSE=0.035), or from the net portal appearance of butyrate and the energy balance of the animals (RMSE=0.050). Models obtained were independent of ruminant species, and presented low interfering factors on the residuals, least square means or individual slopes. The model equations highlighted the importance of considering the physiological state of animals when predicting splanchnic metabolism. This work showed that it is possible to use simple predictors to accurately predict the amount and nature of ketogenic nutrients released towards peripheral tissues in both sheep and cattle at different physiological status. These results provide deeper insight into biological processes and will contribute to the development of improved tools for dietary formulation.

Temporal localized structures in photonic crystal fibre resonators and their spontaneous symmetry-breaking instability.

We investigate analytically and numerically the formation of temporal localized structures (TLSs) in an all photonic crystal fibre resonator. These dissipative structures consist of isolated or randomly distributed peaks in a uniform background of the intensity profile. The number of peaks and their temporal distribution are determined solely by the initial conditions. They exhibit multistability behaviour for a finite range of parameters. A weakly nonlinear analysis is performed in the neighbourhood of the first threshold associated with the modulational instability. We consider the regime where the instability is not degenerate. We show that fourth-order dispersion affects the threshold associated with the formation of bright TLSs. We estimate both analytically and numerically the linear and nonlinear corrections to the velocity of moving temporal structures induced by spontaneous broken reflection symmetry mediated by third-order dispersion. Finally, we show that third-order dispersion affects the threshold associated with the moving TLSs.

[Supracondylar fractures of the humerus in children]. / Les lésions nerveuses dans les fractures supra-condyliennes de l'humérus chez l'enfant.

PURPOSE OF THE STUDY: The most frequent type of elbow fracture in children is by far the supracondylar fracture. This type of fracture also raises the greatest risk of nerve injury. We wanted to study the clinical and prognostic features of nerve injuries in children presen-ting supracondylar fractures of the humerus. MATERIAL AND METHODS: We analyzed the files of 55 children with nerve lesions identified among 1 180 files on supracondylar fractures in children. Most presented Lagrange and Ribault stage IV fractures. Nerve injuries involved the radial nerve (n=28), medial nerve (n=20), and ulnar nerve (n=7). The nerve injury was diagnosed before treatment in 32 children, and after treatment in 23. When nerve injury was identified before treatment, closed reduction had been used for eleven fractures and open reduction for 21. Nerve injury identified after treatment was found in eleven fractures after closed reduction and in 12 fractures after open reduction. RESULTS: When nerve injury was recognized at the initial examination, spontaneous nerve recovery was achieved in all cases, irrespective of the treatment modality, within a maximum of four months. When nerve injury was recognized after treatment, spontaneous nerve recovery was obtained in twenty cases. Time to recovery was longer. The three other cases required nerve exploration with neurolysis for two and a nerve graft for one. DISCUSSION: Nerve injury discovered after treatment is either caused by or aggravated by the treatment. Prognosis is less favorable than for injuries discovered at the initial examination. This highlights the importance of carefully searching for nerve deficit, even partial deficiency, in all children presenting a supracondylar fracture of the humerus. It also emphasizes the importance of care in obtaining bone reduction if the initial examination did not reveal any nerve deficit.