Models to predict nitrogen excretion from beef cattle fed a wide range of diets compiled from South America.

The objective of this meta-analysis was to develop and evaluate models for predicting nitrogen (N) excretion in feces, urine, and manure in beef cattle in South America. The study incorporated a total of 1,116 individual observations of N excretion in feces and 939 individual observations of N excretion in feces and in urine (g/d), representing a diverse range of diets, animal genotypes, and management conditions in South America. The dataset also included data on dry matter intake (DMI; kg/d) and nitrogen intake (NI; g/d), concentrations of dietary components, as well as average daily gain (ADG; g/d) and average body weight (BW; kg). Models were derived using linear mixed-effects regression with a random intercept for the study. Fecal N excretion was positively associated with DMI, NI, nonfibrous carbohydrates, average BW, and ADG and negatively associated with EE and CP concentration in the diet. The univariate model predicting fecal N excretion based on DMI (model 1) performed slightly better than the univariate model, which used NI as a predictor variable (model 2) with a root mean square error (RMSE) of 38.0 vs. 39.2%, the RMSE-observations SD ratio (RSR) of 0.81 vs. 0.84, and concordance correlation coefficient (CCC) of 0.53 vs. 0.50, respectively. Models predicting urinary N excretion were less accurate than those derived to predict fecal N excretion, with an average RMSE of 43.7% vs. 37.0%, respectively. Urinary and manure N excretion were positively associated with DMI, NI, CP, average BW, and ADG and negatively associated with neutral detergent fiber concentration in the diet. As opposed to fecal N excretion, the univariate model predicting urinary N excretion using NI (model 10) performed slightly better than the univariate model using DMI (model 9) as predictor variable with an RMSE of 36.0% vs. 39.7%, RSR 0.85 vs. 0.93, and CCC of 0.43 vs. 0.29, respectively. The models developed in this study are applicable for predicting N excretion in beef cattle across a broad spectrum of dietary compositions and animal genotypes in South America. The univariate model using DMI as a predictor is recommended for fecal N prediction, while the univariate model using NI is recommended for predicting urinary and manure N excretion because the use of more complex models resulted in little to no benefits. However, it may be more useful to consider more complex models that incorporate nutrient intakes and diet composition for decision-making when N excretion is a factor to be considered. Three extant equations evaluated in this study have the potential to be used in tropical conditions typical of South America to predict fecal N excretion with good precision and accuracy. However, none of the extant equations are recommended for predicting urine or manure N excretion because of their high RMSE, and low precision and accuracy.

Odd-chain fatty acids as an alternative method to predict ruminal microbial nitrogen flow of feedlot Nellore steers fed grain-based diets supplemented with different nitrogen sources.

This study aimed to evaluate the use of total odd-chain fatty acids (OCFA) as a marker to estimate microbial nitrogen flow (MicN) and calculate the efficiency of microbial nitrogen synthesis (EMNS) in Nellore steers fed high-concentrate diets supplemented with different nitrogen supplements (NS). Ruminally and duodenally cannulated Nellore steers (n = 6; 354 ± 12 kg) were used in a 6 × 6 repeated switchback design balanced for residual effects. Treatments were arranged in a 3 × 3 factorial of three nitrogen (N) supplements (urea plus soybean meal; corn gluten meal; dried distillers' grains plus solubles) and three microbial markers (OCFA; double-labeled urea, 15N; microbial nucleic acid bases, MNAB). The total mixed ration was composed of fresh chopped sugarcane as the forage source in an 83:17 concentrate: forage ratio (dry matter basis). Linear regression was used to develop predictions of MicN from OCFA using 15N and MNAB as response variables. Microbial N flow was underestimated by the MNAB marker compared to 15N. Neither NS nor their respective interactions with the marker methods (MM) affected MicN or EMNS (P > 0.05). However, MicN was different for 15N and MNAB (P > 0.001 for both treatments). Marker methods affected EMNS in all energetic bases (total digestible carbohydrates P < 0.001; rumen-fermentable carbohydrates P < 0.001; organic matter truly degradable in the rumen P < 0.001). Equations that utilized OCFA as a regressor to predict MicN under different MM resulted in good fits of the data as observed by the coefficient of determination (R2; 15N = 0.78; MNAB = 0.69). Microbial N flow estimated from OCFA was overpredicted (15N by 7.46%; MNAB by 4.30%) compared with observed values. The OCFA model presented a small slope bias when methodological validation was applied (15N = 0.96%; MNAB = 3.90%), ensuring reliability of the proposed alternative method. Based on the conditions of this experiment, OCFA may be a suitable alternative to other methods that quantify MicN under different dietary conditions.

Nutritional strategies that maximize microbial nitrogen supply to the small intestine may improve cattle performance. Nevertheless, in vivo quantification generally requires sensitive or expensive methods and often yields highly variable results. In the present work, we investigated the use of duodenal odd-chain fatty acids (OCFA) as an alternative method to predict microbial nitrogen flow (MicN) and calculated its efficiency on different energetic bases under different dietary nitrogen supplements. We utilized total OCFA flow (TOCFAf) to predict MicN by two well-established conventional methods: 1) 15N, considered the gold standard and 2) microbial nucleic acid bases. Models presented a positive relationship between TOCFDf and response variables, and under validation, both demonstrated low estimation bias. Under the conditions of this experiment, OCFA appeared to serve as an alternative marker to quantify ruminal MicN for beef cattle.

Fatty acid profile and carcass traits of feedlot Nellore cattle fed crude glycerin and virginiamycin.

Forty-eight bulls with an initial body weight (BW) of 408.4 ±â€¯22.2 kg (age = 21 ±â€¯2 months) were used in a randomized complete block design arranged in a 2 × 2 factorial design. The treatments were diets without virginiamycin (VM-) or with virginiamycin, at 25 mg/kg of dry matter (DM, VM+), and diets without crude glycerin (CG-) or with crude glycerin, at 100 g/kg DM (CG+). The cold carcass weight and cold carcass dressing (P ≤ 0.05) was greater in bulls fed crude glycerin diets. Total unsaturated fatty acids (UFA) were 6.08% higher, and cooking weight loss was 10% lower in bulls fed CG+ diets, compared to bulls fed CG- diets (P = 0.0081). Crude glycerin at 100 g/kg DM could be a suitable replacement for VM, as it led to a slight increase in UFA deposition in meat. However, simultaneous administration of VM and CG did not positively affect performance and carcass traits of feedlot Nellore cattle.

Comparison of laboratory methods to assess fiber contents in feedstuffs / Comparación de métodos de laboratorio para determinar el contenido de fibra en alimentos para animales / Comparação de metodologias laboratoriais para determinação de fibras em alimentos

Summary Background: the conventional method of fiber analysis using neutral detergent fiber (NDF) and acid detergent fiber (ADF) was proposed by Peter Van Soest. The main advantage of this method is the precision of results; however, reagents are costly and laboratory work requires long runtime and labor. Objective: to compare analytical data from different methodologies used to assess NDF and ADF contents. Methods: means obtained with the conventional method were compared through Dunnett's test (α=5%) with values from alternative methods using autoclave as the digester system. A completely randomized design in a 4 x 2 factorial arrangement was used. Results: NDF content through alternative methods was assessed for Tifton 85 hay, babassu meal and sugarcane, whereas ADF was only determined for babassu meal. NDF and ADF did not differ (p(0.05) between non-sequential or sequential analysis for all the feedstuffs and methods studied, except for ADF in corn silage. Conclusion: alternative methodologies allow reducing operating costs and time but lack uniformity and accuracy for analyzing ADF in corn silage.

Resumen Antecedentes: la determinación de los valores de fibra detergente neutra (FDN) y fibra detergente ácida (FDA) es de gran importancia en la nutrición animal, siendo el método tradicional de análisis el propuesto por Van Soest. Este método presenta como ventaja principal la precisión de los resultados, sin embargo la rutina de laboratorio en su ejecución implica mucho tiempo debido a sus etapas manuales, además de ser un método de alto costo que genera considerables proporciones de residuos químicos. Objetivo: evaluar diferentes metodologías propuestas para la análisis de las FDN y FDA mediante la medición de los datos analíticos. Métodos: las medias obtenidas por el método tradicional fueron comparadas con las medias de métodos alternativos que usan una autoclave como sistema digestor por el test de Dunnette (α=5%). Un diseño completamente aleatorio, en un diseño factorial 4x2 fue adoptado. Resultados: los métodos alternativos fueron recomendadas para las determinaciones de FDN por el heno de Tifton 85, salvado de harina de babasú y caña de azúcar, mientras que las determinaciones de los valores de FDA apenas para el salvado de harina de babasú. Los resultados de los análisis de FDN y FDA no fueron significativamente diferentes (p(0.05) entre los análisis no secuencial y secuencial, en todos los alimentos y métodos estudiados, a excepción de la determinación de FDA en el ensilaje de maíz. Conclusión: las metodologías alternativas permitieron ganancias significativas con la reducción de costos operacionales y del tiempo de análisis, pero sin uniformidad en la precisión de los análisis involucrados.

Resumo Antecedentes: as determinações dos teores de fibra em detergente neutro (FDN) e em fibra em detergente ácido (FDA) são de extrema importância na nutrição animal, tendo como método convencional de análise o proposto por Van Soest. Esse método apresenta como principal vantagem a precisão dos resultados, no entanto, a rotina laboratorial da sua execução demanda muito tempo por possuir etapas manuais, além do que é um método de custo elevado e que gera resíduos químicos em proporções consideráveis. Objetivo: avaliar diferentes metodologias propostas para análise da FDN e FDA, através da verificação dos dados analíticos. Métodos: as médias obtidas pelo método convencional foram comparadas com as médias de métodos alternativos que utilizam a autoclave como sistema digestor, pelo teste de Dunnette (α=5%). O delineamento adotado foi o inteiramente casualizado, em um esquema fatorial 4x2. Resultados: os métodos alternativos foram recomendados para determinação de FDN no feno de Tifton 85, farelo de babaçu e cana-de-açúcar, enquanto para as determinações dos teores de FDA, apenas no farelo de babaçu. A precisão observada nas análises dos teores de FDN e FDA não diferiram significativamente (p(0.05) quanto a análise não sequencial e sequencial, em todos os alimentos e métodos estudados, com exceção da determinação de FDA na silagem de milho. Conclusão: as metodologias alternativas permitiram ganhos significativos com a redução dos custos operacionais e do tempo da análise, mas sem uniformidade na precisão das análises desenvolvidas.

Parameters of fermentation and rumen microbiota of Nellore steers fed with different proportions of concentrate in fresh sugarcane containing diets.

The objective of this study was to evaluate the effect of a fresh sugarcane-based diet and different roughage-to-concentrate ratios (70:30, 60:40, 40:60 and 20:80) on the rumen microbiota associated with rumen fermentation parameters and the intake and apparent digestibility of nutrients in Nellore steers. Eight rumen-cannulated Nellore steers (331 ± 8 kg BW) were distributed in a double 4 × 4 Latin square design balanced for the control of the residual effect. The ruminal pH decreased (p < 0.01) and the concentrations of N-NH3, isovaleric and valeric acids increased linearly (p < 0.05) with an increase dietary concentrate level. Furthermore, an increased concentrate proportion reduced the population of Fibrobacter succinogenes and Ruminococus flavefaciens (p < 0.01) and increased the population of Selenomonas ruminantium and Megasphaera elsdenii (p < 0.01). The protozoa count revealed a predominance of the genus Entodinium. The synthesis of microbial N [g/d] and the efficiency of microbial synthesis [g of microbial N/kg of organic matter apparently digested in the rumen] increased as the proportion of concentrate was increased (p < 0.05). Therefore, it can be concluded that an increasing proportion of concentrate in sugarcane-containing diets enhances the synthesis of microbial protein and does not alter the fibre digestibility, although the population of fibre fermenting bacteria was reduced.

Effect of different levels of concentrate on ruminal microorganisms and rumen fermentation in Nellore steers.

The aim of this study was to investigate the effect of different dietary levels of concentrate on feed intake, digestibility, ruminal fermentation and microbial population in steers. Eight Nellore steers fitted with ruminal cannulas were used in a double 4 × 4 Latin square design experiment. The dietary treatments consist of four different proportions of concentrate to roughage: 30:70, 40:60, 60:40 and 80:20% in the dry matter, resulting in Diets 30, 40, 60 and 80, respectively. The roughage was corn silage, and the concentrate was composed of corn, soybean meal and urea. Apparent digestibility of organic matter and crude protein showed a linear association with concentrate proportion (p = 0.01), but the increased concentrate levels did not affect the digestibility of fibre. The lowest ruminal pH-values were observed in animals fed with Diet 80, remaining below pH 6.0 from 6 h after feeding, while in the other diets, the ruminal pH was below 6.0 not before 12 h after feeding. After feeding Diet 80, the ammonia concentration in the rumen was significantly the highest. Higher dietary concentrate levels resulted in a linear increase of propionic acid concentrations, a linear reduction of the ratio acetic acid to propionic acid (p < 0.01) and a linear increased synthesis of microbial nitrogen (p < 0.001). The predicted production of methane was lower in diets with greater amounts of concentrate (p = 0.032). The population of methanogens, R. flavefaciens and R. albus decreased with higher concentrate levels, while the population of S. ruminantium increased (p < 0.05). The results indicate that greater amounts of concentrate do not decrease ruminal pH-values as much as expected and inhibit some cellulolytic bacteria without impairing the dry matter intake and fibre digestibility in Nellore steers.

Effect of Lipid Sources with Different Fatty Acid Profiles on Intake, Nutrient Digestion and Ruminal Fermentation of Feedlot Nellore Steers.

The present study was conducted to determine the effect of lipid sources with different fatty acid profiles on nutrient digestion and ruminal fermentation. Ten rumen and duodenal fistulated Nellore steers (268 body weight±27 kg) were distributed in a duplicated 5×5 Latin square. Dietary treatments were as follows: without fat (WF), palm oil (PO), linseed oil (LO), protected fat (PF; Lactoplus), and whole soybeans (WS). The roughage feed was corn silage (600 g/kg on a dry matter [DM] basis) plus concentrate (400 g/kg on a DM basis). The higher intake of DM and organic matter (OM) (p<0.001) was found in animals on the diet with PF and WF (around 4.38 and 4.20 kg/d, respectively). Treatments with PO and LO decreased by around 10% the total digestibility of DM and OM (p<0.05). The addition of LO decreased by around 22.3% the neutral detergent fiber digestibility (p = 0.047) compared with other diets. The higher microbial protein synthesis was found in animals on the diet with LO and WS (33 g N/kg OM apparently digested in the rumen; p = 0.040). The highest C18:0 and linolenic acid intakes occurred in animals fed LO (p<0.001), and the highest intake of oleic (p = 0.002) and C16 acids (p = 0.022) occurred with the diets with LO and PF. Diet with PF decreased biohydrogenation extent (p = 0.05) of C18:1 n9,c, C18:2 n6,c, and total unsaturated fatty acids (UFA; around 20%, 7%, and 13%, respectively). The diet with PF and WF increased the concentration of NH3-N (p<0.001); however, the diet did not change volatile fatty acids (p>0.05), such as the molar percentage of acetate, propionate, butyrate and the acetate:propionate ratio. Treatments PO, LO and with WS decreased by around 50% the concentration of protozoa (p<0.001). Diets with some type of protection (PF and WS) decreased the effects of lipid on ruminal fermentation and presented similar outflow of benefit UFA as LO.

Lipid Sources with Different Fatty Acid Profile Alters the Fatty Acid Profile and Quality of Beef from Confined Nellore Steers.

The present study was conducted to determine the effects of lipid sources with different fatty acids profile on meat fatty acids profile and beef quality traits of Nellore. A total of 45 Nellore animals with an average initial body weight of 419±11 kg (at 15±2 mo) were distributed in a completely randomized design consisting of 5 treatments and 9 replicates. The roughage feed was maize silage (600 g/kg on a dry matter [DM] basis) plus concentrate (400 g/kg on a DM basis). The dietary treatments were as follows: without fat (WF), palm oil (PO), linseed oil (LO), protected fat (PF), and soybean grains (SG). No effects of lipid sources were observed (p>0.05) on beef color, pH, water-holding capacity, and sarcomere length. Beef from cattle fed PO had greater shear-force values (p<0.05) compared to beef from cattle fed WF. Deposition of main unsaturated fatty acids (oleic, linoleic, and linolenic) was greater in treatments WF, SG, and LO, respectively, while the values of conjugated linoleic acid (CLA) were greater when animals were fed LO. The inclusion of LO in the diet enhances the concentration of CLA in longissimus muscle and subcutaneous fat besides improving the atherogenicity index and elongase activity. As such, LO can be used with the aim to improve the quality of beef from confined Nellore cattle. Conversely, the use of PO is not recommended since it may increase the concentration of undesirable unsaturated fatty acids in muscle and subcutaneous fat, shear-force and the atherogenicity index.