IntroductionThis study aimed to evaluate the effects of sources of non-protein nitrogen (NPN) or rumen undegradable protein (RUP) as supplements on intake, nutrient digestibility, fermentation parameters, and ruminal microbiota in Nellore steers grazing during the dry season.MethodsThe experiment was conducted during the dry season from September to October 2018, in a grazing area of Urochloa brizantha (A. Rich.) Stapf. cv. Xaraés. Eight rumen-and duodenum-cannulated Nellore steers were used in a 4 × 4 Latin square design (2 treatments and 2 periods) balanced for residual effects. The treatments included (1) mineral salt with urea (SMU), formulated to meet 50% of the steer RDP requirement as NPN; and (2) supplementation with corn gluten meal (GLU; 0.3% of body weight) as a source of RUP, with added mineral salt.ResultsGLU supplementation significantly increased supplement intake (p < 0.05) and tended to decrease the intake of forage NDF. Although GLU supplementation improved NDF digestibility, no significant differences were observed in the digestibility of DM, OM, or CP between the treatments (p > 0.05). GLU supplementation significantly increased the relative abundance of several genera, including Ruminococcus 1, Ruminococcus 2, Erysipelotrichaceae UCG-004, Thermoplasmatales Incertae Sedis, Lachnospiraceae XPB1014, Anaeroplasma spp., Anaerotruncus spp. and Eubacterium ruminantium (p < 0.05). The PCA biplot revealed positive associations between GLU supplementation and greater ruminal abundance of Prevotellaceae UCG-004 and Bacteroidetes, as well as with higher concentrations of butyrate, propionate, and valerate acids.DiscussionSupplementation with GLU as a source of RUP in grazing steers during the dry season modulated the rumen microbiota by increasing the abundance of key fibrolytic bacteria and improved fiber digestibility.

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. The models developed in this study to predict N excretion in beef cattle can help to improve the environmental and economic sustainability of beef production systems in South America. Reductions in nitrogen (N) excretion in beef cattle not only yield environmental advantages but also confer economic benefits associated with reduced purchase of protein feed ingredients. As measuring N excretion under farm conditions is not feasible, models that can accurately predict N excretion using variables that are more easily obtained in beef production systems are needed. A meta-regression analysis was conducted to develop models that can predict N excretion in feces, urine, and manure in beef cattle in South America. The univariate model using dry matter intake as a predictor is recommended for fecal N prediction, while the univariate model using N intake is recommended for predicting urine and manure N excretion because the use of more complex models resulted in little to no benefits. However, more complex models that incorporate nutrient intakes and diet composition might be more useful for decision-making when N excretion is a factor to be considered. Such models enable simulations of N excretion with modifications to diet composition with similar accuracy. 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.

This study evaluated the effects of increasing levels of crude glycerol (CG) on the effective degradability of neutral detergent fiber (EDNDF) in Pennisetum clandestinum Hochst. Ex Chiov (kikuyu forage) and ruminal fermentation parameters in grazing dairy cows. Four non-lactating cannulated Holstein cows were used in a 4 × 4 Latin square design. Treatments consisted of CG infusion in the rumen at the following levels: 0 (G0), 500 (G500), 1000 (G1000), and 1500 (G1500) g/animal/day. Two kikuyu forages harvested (D) at 35 (DR35) and 45 (DR45) days of regrowth were incubated in the rumen for 72 h. The infusion of CG into the rumen increased (p < 0.05) EDNDF in both incubated forages. Total volatile fatty acids (VFAs) and pH values in the ruminal fluid were unaffected (p > 0.05) by the infusion of CG. However, propionate and butyrate molar proportions increased (p < 0.05) at the expense of acetate at all CG levels. In addition, the NH3-N levels decreased (p < 0.05) by approximately 20% with the infusion of 1000 and 1500 g of CG. In conclusion, supplementation with CG increases ruminal EDNDF, improving rumen fermentation dynamics in cows grazing kikuyu forage under tropical conditions. This greater EDNDF was achieved for both harvesting times.

This study aimed to investigate changes in feed intake and ruminal environmental parameters during a high-lipid diet transition in cattle. Eight Nellore steers were fed a control diet composed of 30% hay and 70% concentrate for 21 days, followed by the inclusion of 60 g/kg dry matter of soybean oil for 21 days. The DM intake expressed as a percentage of BW 21 days after lipid inclusion was lower (1.75% BW) than that observed during the control diet feeding (1.81% BW) (P<0.01). Steers fed the control diet had a lower pH than the ruminal pH recorded on days 7, 14, and 21 after lipid inclusion (P=0.034). Lower total short-chain fatty acid production in the rumen and lower microbial nitrogen synthesis were observed on day 7 after lipid inclusion compared to values found when steers were fed the control diet and on days 14 and 21 after lipid inclusion (P=0.041). Lipid inclusion in the diet decreased the population of protozoa on days 7, 14, and 21 (P<0.001). The abundances of R. albus and F. succinogenes were higher when steers were fed the control diet than the abundance observed on days 7, 14, and 21 after lipid inclusion in the diet (P<0.05). The first seven days of lipid diet inclusion are considered the most critical for ruminal adaptation, involving reductions in fibrolytic bacteria and changes in fermentation parameters. After 14 days the rumen showed signs of recovery and adaptation.

-The objectives were to evaluate the effects of monensin and virginiamycin, alone or combined, on supplemented Nellore cattle grazing tropical grass during the rainy season. Two experiments were conducted simultaneously to evaluate intake, digestibility, CH4 emissions, blood parameters, performance, and carcass characteristics (Exp. 1), and ruminal fermentation and relative abundance of ruminal microorganisms (Exp. 2). Animals (n = 92 Exp. 1 and n = 12 Exp. 2) were distributed in a completely randomized design and allocated in twelve paddocks composed of Urochloa brizantha (A. Rich.) Stapf. cv. Xaraes. A protein-energetic supplementation of 3 g/kg of BW per day was provided to all animals. Supplements were: without additives (WA), monensin alone at 80 mg/kg of product (MN), virginiamycin alone at 150 mg/kg of product (VM), and monensin (80 mg/kg of product) combined with virginiamycin (150 mg/kg of product; MNVM). Treatments did not affect intakes of total dry matter (DM), supplement DM, and nutrients. However, the intakes of forage DM and crude protein decreased in cattle fed MNVM compared with animals fed WA, MN, and VM. Total volatile fatty acids increased in animals fed VM. Ruminal NH3-N decreased, and pH increased in animals fed MN, VM, and MNVM. Relative abundance of total F. succinogenes and S. ruminantium decreased and R. flavefaciens increased in animals fed MN and VM at d 118. Treatments had no effect on enteric CH4 emissions. The average daily gain (ADG) and total gain were greater in cattle fed MNVM than in cattle fed MN. Combination of monensin and virginiamycin altered the rumen microbial populations but did not decrease enteric CH4 emissions. However, it decreased forage dry matter intake without altering the ADG and total weight gain, leading to an increase in feed efficiency. Results from this study indicate an advantage in including feed additives combined in the diet of supplemented Nellore cattle grazing tropical grass during the rainy season.

The objective was to evaluate the supplementation strategy’s effect on beef cattle during the growing phase and two systems during the finishing phase. One hundred and twenty young bulls were randomly divided in a 2 × 2 factorial design to receive either mineral (ad libitum) or protein + energy (3 g/kg body weight (BW)/day) during the growing phase and pasture plus concentrate supplementation (20 g/kg BW/day) or feedlot (25:75% corn silage:concentrate) during the finishing phase. Feedlot-fed bulls had meat (Longissimus thoracis—LT) with a higher content of lipids and saturated and monounsaturated fatty acids and a greater upregulation of stearoyl-CoA desaturase and sterol regulatory element-binding protein-1c than animals that fed on pasture (p < 0.05). On the other hand, pasture-fed bulls had meat with a higher content of α-linoleic acid, linolenic acid, and n6 and a greater n6:n3 ratio compared to the feedlot-fed group (p < 0.05). In addition, meat from pasture-fed bulls during the finishing phase had 17.6% more isocitrate dehydrogenase enzyme concentration than the feedlot group (p = 0.02). Mineral-fed and pasture-finished bulls showed down-regulation of peroxisome proliferator-activated receptor gamma (p < 0.05), while the bulls fed protein + energy and finished in the feedlot had higher carnitine palmitoyltransferase 2 expression (p ≤ 0.013). In conclusion, mineral or protein + energy supplementation in the growing does not affect the fatty acid composition of intramuscular fat of LT muscle. In the finishing phase, feeding bulls in the feedlot upregulates the lipogenic genes and consequently improves the intramuscular fat content in the meat.

This study aimed to evaluate the effects of supplementation with non-protein nitrogen (NPN) or ruminal undegradable protein (RUP) on intake, digestibility, and amino acid (AA) use efficiency of Nellore cattle grazing during the dry season. Eight Nellore steers (12 ± 2 months old) were used in quadruplicate Latin squares (2 × 2). The animals were placed on Urochloa brizantha cv. Xaraés under continuous grazing. The treatments included the following: (1) urea supplementation (NPN) and (2) supplementation of corn gluten meal 60 (CGM, RUP). Animals supplemented with CGM showed higher intakes of dry matter (DM) supplement, total AA, essential AA, and individual AA. The supplementation did not affect the total AA digestibility, total AA flux, and the AA fluxes of microbial origin and RUP from the diet (p > 0.05). The ruminal microorganism origin flux of total AA to the duodenum was 44.5% and 52.7% for animals supplemented with NPN and CGM, respectively. Animals supplemented with CGM showed an increase in blood concentrations of isoleucine (+19.09 μmol/L), cystine (+27.29 μmol/L), and albumin (+0.11 g/dL) (p < 0.05), but this increase was not accompanied by an improvement in N use efficiency of steers (p > 0.05). RUP supplementation via CGM can be an efficient nutritional strategy to enhance the intake and absorption of AA by Nellore cattle grazing low-quality forage during the dry season.

The effects of sources of rumen undegradable protein (RUP) in diets on methane (CH 4 ), nitrous oxide (N 2 O) and ammonia (NH 3 ) emissions from the manure of feedlot-finished cattle were evaluated. We hypothesized that the use of different RUP sources in diets would reduce N loss via urine and contribute to reduced N 2 O, CH 4 and NH 3 emissions to the environment. Nellore cattle received different diets (18 animals/treatment), including soybean meal (SM, RDP source), by-pass soybean meal (BSM, RUP source) and corn gluten meal (CGM, RUP source). The protein source did not affect the N and C concentration in urine, C concentration in feces, and N balance (P > 0.05). The RUP sources resulted in a higher N 2 O emission than the RDP source (P = 0.030), while BSM resulted in a higher N 2 O emission than CGM (P = 0.038) (SM = 633, BSM = 2521, and CGM = 1153 g ha −2 N–N 2 O); however, there were no differences in CH 4 and NH 3 emission (P > 0.05). In conclusion, the use of RUP in diets did not affect N excretion of beef cattle or CH 4 and NH 3 emission from manure, but increased N 2 O emission from the manure.

The aim of this study was to evaluate the effects of supplementation (3 g/kg BW) of RUP rumen undegradable protein (RUP) with different amino acid profile on the intake, rumen fermentation parameters, total-tract apparent digestibility, nitrogen balance, and performance of beef cattle grazing pasture in the rainy season. Two experiments were carried out simultaneously to evaluated intake and metabolism parameters (Exp.1) and animal performance (Exp.2). Exp.1 lasted 84 days and 9 castrated Nellore steers cannulated in the rumen and duodenum (18 +/- 2 months old and 350 +/- 78 kg initial BW) were assigned in 3 simultaneous 3 x 3 Latin squares design. Exp.2 lasted 112 days and 96 young Nellore bulls (12 +/- 3 months old and 240 +/- 19 kg initial BW) were assigned in a randomized block design. Animals were kept on pasture of Urochloa brizantha cv. Xarae acute accent s (CP = 12.3%), in continuous grazing and put and take method. The treatments were: 1) mineral supplementation (MS; ad libitum), 2) RUP supplementation with corn gluten meal 60 (CGM; 3 g/kg of body weight [BW] per day), and 3) RUP supplementation with protected soybean meal (PSBM; 3 g/kg of BW per day). The supplementation of RUP feed sources with different amino acid profile increased the intakes of DM supplement and CP, and the total-tract apparent digestibility of CP. In addition, animals supplemented with RUP, regardless the amino acid profile, had an increase in the excretion of N in feces and urine. However, both RUP supplementation increased final BW and total BW gain. The ADG of the animals was improved with an additional gain of 195 g/day for CGM and PSBM compared to MS, and no differences between RUP sources were observed. No differences in the intake of DM (kg and % of BW), OM, and forage DM, ruminal pH, and microbial-N across treatments. Animals supplemented PSBM had a greater NDF intake and total VFA concentration compared to CGM. Retaine-N (g/d) was increased by PSBM supplementation compared to MS, but it did not differ between RUP sources. Taken together, the results demonstrate that supplementation of 3 g/kg of BW of RUP with different amino acid profile during the rainy season is an effective nutritional strategy used to improve performance of growing beef cattle grazing pasture. In addition, RUP supplementation improved N metabolism, with PSBM resulting in greater N retained compared to MS supplementation.

The objective of this study was to evaluate the effects of mineral or protein-energy supplementation and animal genetic groups on rumen fermentation, digestibility and microorganisms of young beef bulls grazing tropical grass during the rainy season. Twelve (nn = 4 per genetic group) ruminally cannulated beef bulls [16 +/- 2 months-old and 411 +/- 34 kg initial body weight (BW)] were used in a cross-over design, with 4 periods, in a 2 x 3 factorial arrangement. Factors included: 1) two supplementation strategies (SS; mineral supplement [30 g/100 kg BW per day] and protein-energy supplement [300 g/100 kg BW per day]); and 2) three genetic groups (GG; Nellore [NL], 1/2Angus1/2Nellore [AN] and Senepol [SN]). Animals were continuously allocated in twelve paddocks composed of Urochloa brizantha (A. Rich.) Stapf. cv. Xarae acute accent s for 126 days during the rainy season. Supplementing animals of all GG with protein-energy supplement resulted in an increase of the intake of DM, OM, CP, EE, NFC and ME, and apparent total-tract digestibility of CP and EE. Additionally, animals fed protein-energy supplement showed highest rumen NH3-N concentration, microbial-N synthesis, and retained-N. However, a decrease in rumen pH and acetate:propionate ratio was observed when animals were fed protein-energy supplement. Except for Ruminococcus flavefaciens, the relative abundance of total Archaea and Prevotella.spp. were increased when animals where fed protein-energy supplement. Moreover, a GG effect was observed on the relative abundance of total Archaea, Prevotella.spp. and Ruminococcus flavefaciens, which were highest in NL, SN and AN animals, respectively. SN animals fed protein-energy supplement showed an increase of Streptococcus bovis and Selenomonas ruminantium relative abundance, while Fibrobacter succinogenes and Ruminococcus albus were highest in NL animals supplement mineral and protein-energy supplement, respectively. In conclusion, protein-energy supplementation to beef bulls grazing high-quality tropical grass is an effective strategy to increase rumen fermentation during the rainy season. In addition, it modulated rumen microorganism leading to an increase in the relative abundance of Prevotella.spp., Streptococcus bovis and Selenomonas ruminatium, and a decrease in acetate:propionate ratio in Senepol animals.

Improving livestock production through nutrition and breeding can increase efficiency and has the potential to mitigate methane (CH4) emissions. Additionally, supplementing beef cattle in the rainy season balances the dietary protein:energy (P:E) ratio, which can increase animal perfor-mance and reduce energy losses from CH4 production. Therefore, the objective of this study was to evaluate the effect of supplementation strategy (SS) and genetic group (GG) on the intake, digestibility, performance, and enteric CH4 emissions of growing beef bulls grazing tropical grass during the rainy season. One hundred sixty-two growing beef bulls averaging (mean +/- SD) 10 +/- 2 months old and 262 +/- 31 kg of initial body weight (BW) were distributed, according to their BW, in a randomized complete block design in a 2 x 3 factorial arrangement. Factors included (1) two SSs (mineral supplementation at 0.3 g/kg of BW per day and a corn-based supplementation at 3 g/kg of BW per day) and (2) three GGs (Nellore [NN], ''ASenepol''ANellore [SN], and ''AAngus''ANellore [AN]). Animals were allocated in 12 paddocks composed of Urochloa brizantha (A. Rich.) Stapf. cv. Xarae acute accent s for 99 days during the rainy season. Regardless of the GG, the intakes of total DM, supplement DM, OM, CP, aNDFom, EE, and NFC were increased in animals sup-plemented with a corn-based supplement. The SN bulls had a greater digestibility of DM, OM, and CP, and animals supplemented with a corn-based supplement had greater CP and EE digestibility. There was an interaction between GG and SS for NFC digestibility, which was decreased in AN animals fed a corn-based supplement. However, the corn-based supplementation improved the animal's performance and carcass characteristics as demonstrated by the increase of final BW (kg), ADG (kg), REA (cm2), and FT (mm). Moreover, NN animals fed a corn-based supplement showed an increase in ADG (kg). An interaction between SS and GG was observed for GPH (kg/ ha) and CaG (kg), with the greatest values observed in NN and SN animals supplemented with a corn-based supplement. Enteric CH4 emissions (g/d, g/kg of DMI, and g/kg of dOM) were lower in animals fed a corn-based supplement. A decrease in CH4 emissions (g/d) was observed in SN compared to NN animals. In addition, there was an interaction between SS and GG for CH4 emissions (g/kg of CaG), with the lowest values for NN and SN animals supplemented with a corn -based supplement. Taken together, our results demonstrate that corn-based supplementation is an effective nutritional strategy for use in the rainy season, especially for NN and SN genetic groups, to improve animal's performance and carcass characteristics and to decrease enteric CH4 emis-sions, per unit of product, of growing beef bulls grazing tropical grass.

We hypothesized that supplementation with rumen undegradable protein (RUP) during the rearing phase mitigates nitrous oxide (N 2 O), methane (CH 4 ), and ammonia (NH 3 ) emissions from excreta of Nellore animals in Urochloa brizantha ‘Xaraés’ pasture. The treatments applied to soil were urine and dung of animals supplemented without RUP or with RUP in the middle and end of the rearing phase. We assessed N 2 O and CH 4 emissions using a static closed chamber and NH 3 emissions using the semi-open static chamber method. No effects were observed for supplement, excreta type, period, or interaction on N 2 O emissions. The mean emission factor was 0.03% of N in the excreta lost as N 2 O. Higher NH 3 losses were observed for the urine treatments in the end period, regardless of the supplement type. The mean NH 3 emission factor for urine was 2.96 and 13.8% for the middle and end periods, respectively, while the mean value for dung was 3.9%. The type of supplement did not affect CH 4 emissions, and the mean dung emission factor was 0.12 kg CH 4 head –1  year –1 . In summary, the supplementation of beef cattle in pastures with RUP did not mitigate NH 3 , N 2 O, and CH 4 emissions from excreta. The excreta emission factors for the GHGs measured, regardless of differences in the type of excreta, type of supplement, and period, were lower than the default value of Intergovernmental Panel on Climate Change revised guidelines. Further studies will be needed to fully understand the mechanisms underlying the effects of RUP on greenhouse gas emissions.

On-farm methane (CH4) emissions need to be estimated accurately so that the mitigation effect of recommended practices can be accounted for. In the present study prediction equations for enteric CH4 have been developed in lieu of expensive animal measurement approaches. Our objectives were to: (1) compile a dataset from individual beef cattle data for the Latin America and Caribbean (LAC) region; (2) determine main predictors of CH4 emission variables; (3) develop and cross-validate prediction models according to dietary forage content (DFC); and (4) compare the predictive ability of these newly-developed models with extant equations reported in literature, including those currently used for CH4 inventories in LAC countries. After outlier's screening, 1100 beef cattle observations from 55 studies were kept in the final dataset (∼ 50 % of the original dataset). Mixed-effects models were fitted with a random effect of study. The whole dataset was split according to DFC into a subset for all-forage (DFC = 100 %), high-forage (94 % ≥ DFC ≥ 54 %), and low-forage (50 % ≥ DFC) diets. Feed intake and average daily gain (ADG) were the main predictors of CH4 emission (g d-1), whereas this was feeding level [dry matter intake (DMI) as % of body weight] for CH4 yield (g kg-1 DMI). The newly-developed models were more accurate than IPCC Tier 2 equations for all subsets. Simple and multiple regression models including ADG were accurate and a feasible option to predict CH4 emission when data on feed intake are not available. Methane yield was not well predicted by any extant equation in contrast to the newly-developed models. The present study delivered new models that may be alternatives for the IPCC Tier 2 equations to improve CH4 prediction for beef cattle in inventories of LAC countries based either on more or less readily available data.

Lay Summary 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. Odd-chain fatty acids may be a suitable alternative marker method to quantify ruminal microbial nitrogen flow in beef cattle. 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 x 6 repeated switchback design balanced for residual effects. Treatments were arranged in a 3 x 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 (R-2; 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.

The objective of this study was to evaluate the effect of previous supplementation strategies (mineral and corn-based supplementation in the growing-phase) on intake and performance of different beef cattle group genotypes in the finishing phase on pasture or feedlot. Two experiments for the finishing phase were conducted simultaneously. For Exp.1, 60 bulls were finished on tropical grass with supplementation. They were distributed in a randomized block design in a 3 x 2 factorial arrangement (three genotypes (Nellore, Senepol x Nellore (1/2Senepol), Angus x Nellore (1/2Angus)) and two growing-phase supplementation strategies (mineral and cornbased supplementation)). They were allocated to 12 paddocks with 1.8 ha of Urochloa brizantha 'Xaraes' per paddock (5 animals/paddock). The animals were supplemented (corn-based supplement at the rate of 20 g/kg body weight [BW]) for 125 days. For Exp.2 60 bulls were finished in individual pens. They were of three genotypes (Nellore, 1/2Senepol, 1/2Angus) from two growing-phase supplementation strategies (mineral and cornbased supplementation) and distributed in a randomized block design allocated to individual pens. In Exp.1 (finish on tropical grass), the genotypes, 1/2 Angus and Nellore bulls showed the greatest initial (end of growing phase treatments) and final body weights (BW), final carcass weight (HCW) and hot carcass yield (HCY) than 1/2. Senepol bulls. Bulls with corn-based supplementation in the growing phase had greater initial (end of growing phase) and final BW and lower feed efficiency (FE) than animal supplementation with mineral in the growing phase. 1/2Senepol showed higher total dry matter (DM, percentage of BW) and forage DM intake than Nellore in the finishing phase. For supplement DM intake, higher values were found for the 1/2. Angus bulls compare 1/2 Senepol. Nellore bulls showed greater DM and OM digestibility than 1/2. Senepol but no different to 1/2 Angus. For experiment 2 (finish in feedlot), 1/2. Angus and 1/2. Senepol bulls had higher ADG than Nellore bulls. 1/2. Angus and Nellore bulls presented the greatest HCW while Nellore bulls had the highest HCY. Daily carcass gain (DCG) in the finishing phase was higher in animals that received only mineral supplementation during the growth phase. 1/2. Angus and 1/2. Senepol showed higher FE than Nellore bulls. Nellore bulls had lower DMI of forage and supplement than 1/2 Angus and 1/2. Senepol.1/2. Angus and Nellore bulls had greater BW at the end of the finishing phase than 1/2. Senepol.The feedlot-finishing system promotes better finishing performance in 1/2. Angus and 1/2. Senepol, thus crossing Nellore with a Bos taurus breed may be a strategy to improve finishing performance and carcass characteristics. Corn-based supplement during the growing phase may be a strategy to improve body weight on entry to a finishing phase, although it may reduce carcass gain in the finishing phase.

An in vitro trial was conducted to evaluate the effects of different unsaturated fatty acids (UFA) sources plus crude glycerin (CGL) on gas production and rumen biohydrogenation (RBH). Incubated diet corresponded to diets containing corn silage (30%) and concentrate (70%) composed of corn, urea, mineral salts, CGL, and different UFA sources as follows: no additional fat (NAF), rumen protected fat (RPF), soybean oil, linoleic acid (LA) or alpha-linolenic acid (LN). Methane concentrations in LA and LN were lower compared to NAF (p < 0.001), but when CH4 was expressed as a proportion of total gas, NAF and RPF showed the greatest values among evaluated UFA sources (p = 0.001). 18:1 t11 concentration showed a faster increase from 0 to 1 h and a slower decrease from 1 to 36 h of incubation, irrespective of UFA source. A higher C18:1 t11 production rate was observed from 1 h to 5 h of incubation, where LA and LN have higher values compared to NAF and RPF diets (p < 0.001). Diets with a high content of LA may be efficient as a nutritional approach to reduce methane production and RBH, resulting in positive effects on vaccenic acid concentrations.

Urea recycling occurs in all mammalian species and represents an important source of ruminal nitrogen (N) for ruminants fed protein-restricted diets. However, its importance for cattle fed adequate amounts of protein and energy remains unclear. Six Nellore feedlot steers fed concentrate-based diets were used in a 6 x 6 Latin square design with a 3 x 2 factorial arrangement of treatments to evaluate ruminal fermentation, urea kinetics, and N excretion. Treatments consisted of 3 protein sources (PS: soybean meal plus urea [SU], corn gluten meal [CGM], and dry distillers grains [DDG]) and 2 inclusion levels (PL; 11% and 14%). Steers were adapted to the diets for 14 d followed by 8 d of sample collection. Feed intake, fecal output, and urine production were measured from day 18 to day 22 of each period. Blood samples were collected every 6 h on day 18. [N-15-N-15]-urea was infused into the jugular vein for 82 h over day 19 to day 22, and measurement of N-15 in background (day 18) and enriched feces and urine (day 21) were used to evaluate urea kinetics. To evaluate the incorporation of recycled urea N into microbial protein (MICP), ruminal and duodenal fluid were collected on day 22. Steers fed SU diets had lower (P < 0.05) nitrogen use efficiency (NUE), greater (P < 0.05) urea-N entry rate (UER), and tended (P < 0.10) to have greater gastrointestinal entry rate of urea-N (GER) compared with those fed CGM or DDG. In addition, steers fed SU had greater (P < 0.05) urea-N returned to ornithine cycle (ROC) compared with those fed CGM or DDG. Increasing PL tended (P < 0.10) to increase UER. The proportion of total microbial N from recycled urea-N was greater (P < 0.05) for steers fed CGM compared with those fed SU and also greater for steers fed diets with 11% CP than for those fed with 14% CP. Diets with 11% CP can be used for Nellore feedlot cattle fed concentrate-based diets without negatively affecting intake, digestibility, and ruminal fermentation. Moreover, diets containing rumen undegradable protein (RUP) feed sources (CGM or DDG) compared with diets with SU markedly increased NUE, while maintaining microbial protein (MICP) synthesis. Results from this study suggest that the equation adopted by NASEM (NASEM. 2016. Nutrient requirements of beef cattle. 8th revised ed. Washington, DC: The National Academies Press) was not accurate in estimating the urea-N used for anabolism (UUA) in Nellore feedlot cattle fed concentrate-based diets.

One hundred and twenty bulls were used in a randomized complete block design in 2 ? 2 factorial arrangement; two supplements during the growing phase: mineral (ad libitum; MIN) or protein + energy [0.3% of body weight (BW)/animal/day; PRE] and two finishing systems: pasture plus concentrate supplementation (2% BW/animal/ day; PASCO) and feedlot (25:75% corn silage:concentrate; FLOT). The supplementation strategy at growing phase did not affect (P 0.050) the pH, shear force, sarcomere length and myofibrillar fragmentation index of the animals. Backfat thickness was increased and meat shear force was decreased (P < 0.050) when the bulls were finished in FLOT. Bulls from PASCO presented an increase (P < 0.050) in the yellowness subcutaneous fat and myoglobin concentration, and a decrease in L* and a* values in meat during storage days. Meat lipid oxidation was decreased (P < 0.011) in bulls fed MIN during the growing phase followed by PASCO. Supplementation used at growing phase did not affect the meat quality of the bulls and the feedlot system slightly improved beef tenderness and colour compared to pasture plus supplementation.

The aim of this study was to determine the effects of different amounts of crude glycerol (CGL) on dry matter intake, milk yield, milk protein yield, and milk fatty acid profile of dairy cows grazing on a Kikuyu-based pasture. Six Holstein cows were used in the first third of lactation (mean ± SD 559 ± 22.5 kg body weight, 43 ± 10 days in milk, and 26.8 ± 1.2 kg milk/day) and were randomized within a replicated 3 × 3 Latin square arrangement. Animals grazed the Kikuyu grass and were supplemented with a commercial energy-protein concentrate at 1.0 kg/4.0 kg of milk. The experimental period was 69 days. The following treatments were administered: CGL0 (control, without glycerol), CGL1 (750 g/cow/day), and CGL2 (1,500 g/cow/day). The addition of 750 and 1,500 g of CGL did not affect grass and concentrate intake (P > 0.05). However, milk yield (FCM 3.5%) increased by 14.2% in the CGL2 group compared to that obtained in the control group (CGL0) (P = 0.02). The addition of 1,500 g of CGL to the diet resulted in a 2.1% greater yield of milk protein compared to that obtained with CGL0 treatment (P = 0.01). Further, the addition of 1,500 g of CGL did not impact grass intake, milk fat concentration, or fatty acid composition (P < 0.05). Thus, the inclusion of CGL as a co-product may be a nutritional strategy to increase the productivity of dairy production systems in tropical perennials, such as Kikuyu grass.

Despite the important role of digesta mean retention time (MRT) on digestive efficiency of ruminants, it is poorly investigated in total gastrointestinal tract (GIT) of growing ruminants, especially in goats. The objective of this study was to evaluate the effect of body weight (BW) and sex on GIT MRT of particles and solutes in growing Saanen goats. A dataset from two studies, comprising 103 individual records of castrated males (n = 36), females (n = 34), and intact males (n = 33) Saanen goats slaughtered at 15, 22, 30, 37, and 45 kg BW, was used. Goats were fed basically with total mixed ration composed by dehydrated corn plant (Zea mays) milled to pass a 10-mm screen, cracked corn grain, and soybean (Glycine max) meal. Variables evaluated were BW, feed intake, feed intake level, composition of ingested diet, wet weight of GIT tissues, wet digesta pool size, digesta composition (dry matter and neutral detergent fiber [NDF]), indigestible NDF:NDF ratio of ingested diet and GIT digesta, MRT of particles (MRTiNDF) and solutes (MRTCr), and reticulorumen selectivity factors (large particles/solutes). Reticulorumen, omasum, abomasum, small intestine, cecum, and colon-rectum segments were evaluated. The dataset was analyzed as mixed models considering sex, BW, and sex x BW interaction as fixed effects, and study and residual error as random effects. Sex did not affect MRTiNDF in any GIT segments. Females and intact males presented similar reticulorumen MRTCr (5.6 h; P = 0.92) and they presented lower reticulorumen MRTCr than castrated males (7.0; P <= 0.04). Total GIT MRTCr was similar between castrated males and females (15.7 h; P = 0.11) and between females and intact males (14.2 h; P = 0.76). Body weight (BW) did not affect MRTiNDF in reticulorumen and colon-rectum and total GIT MRTCr (P >= 0.11). Reticulorumen and omasum MRTCr increased as BW increased (P < 0.01), and abomasum MRTCr decreased as BW increased (P = 0.02). Feed intake, and wet tissues and wet pool size of all GIT segments increased as BW increased, except abomasum wet pool size (P <= 0.01). The mechanism related to sex effect on MRT has to be elucidated. Reticulorumen MRTiNDF and total GIT MRTCr were modulated by intake and capacity of reticulorumen and GIT, respectively. On the other hand, reticulorumen MRTCr seemed to be regulated by reticulo-omasal orifice opening and saliva secretion.