BackgroundThe selection of beef cattle for feed efficiency (FE) traits is very important not only for productive and economic efficiency but also for reduced environmental impact of livestock. Considering that FE is multifactorial and expensive to measure, the aim of this study was to identify biological functions and regulatory genes associated with this phenotype.ResultsEight genes were differentially expressed between high and low feed efficient animals (HFE and LFE, respectively). Co-expression analyses identified 34 gene modules of which 4 were strongly associated with FE traits. They were mainly enriched for inflammatory response or inflammation-related terms. We also identified 463 differentially co-expressed genes which were functionally enriched for immune response and lipid metabolism. A total of 8 key regulators of gene expression profiles affecting FE were found. The LFE animals had higher feed intake and increased subcutaneous and visceral fat deposition. In addition, LFE animals showed higher levels of serum cholesterol and liver injury biomarker GGT. Histopathology of the liver showed higher percentage of periportal inflammation with mononuclear infiltrate.ConclusionLiver transcriptomic network analysis coupled with other results demonstrated that LFE animals present altered lipid metabolism and increased hepatic periportal lesions associated with an inflammatory response composed mainly by mononuclear cells. We are now focusing to identify the causes of increased liver lesions in LFE animals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2292-8) contains supplementary material, which is available to authorized users.

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Data from three comparative slaughter experiments with individually fed Nellore bulls (n = 31) and steers (n = 66) were utilized to determine their NEm and NEg requirements when fed high-forage diets. The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict NEm and NEg requirements. The Nellore bulls (Trial 1) were divided into two intake levels (ad libitum and 65% of the ad libitum). The steers (Trials 2 and 3) were allocated to three intake levels (ad libitum and 55 and 70% of the ad libitum). In both trials, there were three slaughter groups within each intake level. The three end points for the bulls were different days on treatment (100, 150, and 190 d and 130, 180, and 200 d, respectively, for older and younger animal subgroups). The steers were slaughtered when animals of the ad libitum treatment reached 400, 440, and 480 kg shrunk BW (SBW) on average for the first, second, and third group, respectively. For all body composition determinations, whole empty body components were weighed, ground, and subsampled for chemical analysis. In each of the trials, initial body composition was determined with equations developed from a baseline slaughter group, using SBW and empty BW (EBW), fat (EBF), and protein (EBP) as variables. The NEm was similar for bulls and steers; NEm averaged 77.2 kcal/ kg0.75 EBW. However, the efficiency of conversion of ME to net energy for maintenance was greater for steers than for bulls (68.8 and 65.6%, respectively), indicating that bulls had a greater ME requirement for maintenance than steers (5.4%; P < 0.05). Our analyses do not support the NRC (2000) conclusion that Nellore, a Bos indicus breed, has a lower net energy requirement for maintenance than Bos taurus breeds. An equation developed with the pooled data to predict retained energy (RE) was similar to the NRC (2000) equation. A second equation was developed to predict RE adjusted for degree of maturity (u): RE = (6.45 - 2.58/u) x EWG x e(0.469) x u), where u = current EBW/final EBW in which final EBW was 365 kg for steers and younger bulls and 456 kg for older bulls at 22% EBF, respectively.

BackgroundFeed intake plays an important economic role in beef cattle, and is related with feed efficiency, weight gain and carcass traits. However, the phenotypes collected for dry matter intake and feed efficiency are scarce when compared with other measures such as weight gain and carcass traits. The use of genomic information can improve the power of inference of studies on these measures, identifying genomic regions that affect these phenotypes. This work performed the genome-wide association study (GWAS) for dry matter intake (DMI) and residual feed intake (RFI) of 720 Nellore cattle (Bos taurus indicus).ResultsIn general, no genomic region extremely associated with both phenotypic traits was observed, as expected for the variables that have their regulation controlled by many genes. Three SNPs surpassed the threshold for the Bonferroni multiple test for DMI and two SNPs for RFI. These markers are located on chromosomes 4, 8, 14 and 21 in regions near genes regulating appetite and ion transport and close to important QTL as previously reported to RFI and DMI, thus corroborating the literature that points these two processes as important in the physiological regulation of intake and feed efficiency.ConclusionsThis study showed the first GWAS of DMI to identify genomic regions associated with feed intake and efficiency in Nellore cattle. Some genes and QTLs previously described for DMI and RFI, in other subspecies (Bos taurus taurus), that influences these phenotypes are confirmed in this study.

a b s t r a c tThe aim was to evaluate growth, carcass traits, feed efficiency reranking, body composition, calpain system activity and meat quality in Nellore steers that were phenotypically ranked for high and low residual feed intake (RFI). Seventy-two Nellore steers (16-21 month-old, 334719 kg BW) had free access to a feedlot diet for 70 d (feeding period 1, P1). Daily dry matter intake (DMI), body weight gain (ADG) and ultrasound carcass traits were measured individually. The 12 lowest and the 12 highest RFI steers were classed as low-and high-RFI groups and were fed for a second feeding period (feeding period 2, P2). Spearman's rank correlation was performed for RFI and gain-to-feed ratio (G:F) measured over P1 and P2. The carcass traits, meat quality and calpain system activity were evaluated at slaughter, and body composition was determined. In P1, low-RFI steers had greater G:F (0.159 vs. 0.134; Po0.001), lower DMI (9.30 vs. 11.1 kg/d; Po0.0001), lower RFI (À 0.80 vs. 0.85 kg/d; Po0.0001), and tended to have lower rates of rump fat gain (4.48 vs. 6.05 mm; P¼ 0.06), but no differences were observed for ADG, BW, and other traits measured by ultrasound (P40.05). In P2, no differences between RFI classes were observed for G:F and DMI as a percentage of BW (P40.05), and small differences were observed for DMI (8.25 vs. 8.99 kg/d, Po0.05) and RFI (À 0.28 vs. þ0.29 kg/d, P¼0.06). The ranking correlations for RFI and G:F measured consecutively in P1 and P2 were low to moderate (r¼ 0.11-0.40). Low-RFI steers had lower requirements of metabolizable energy (ME) for maintenance (131 vs. 160 Mcal/kg EBW 0.75 d À 1 , Po0.05), but no differences were observed for fat and protein gain, retained energy and efficiency of ME use for gain (P40.05). No differences between low-and high-RFI steers were observed for carcass traits at slaughter; however, low-RFI steers had 8.1 kg less gastrointestinal fat than high-RFI steers. There were no RFI effects on meat shear force and the activities of m-calpain, m-calpain and calpastatin (P40.05). High-RFI steers had greater MFI in 1 d aged LM (53.9 vs. 40.8, Po0.05). The variation in feed efficiency between high-and low-RFI Nellore steers is related to differences in energy requirements and deposition of fat on internal organs. The ranking for feed efficiency is altered as cattle become older. The selection for improved RFI in Nellore cattle may reduce feed requirements for beef production without affecting meat tenderness and enzymatic activity of the calpain system.

This study was conducted to evaluate the effects of flint corn processing method (CPM) and level of NDF from roughage (rNDF) on performance, carcass characteristics, and starch utilization by finishing Nellore-based cattle fed high-concentrate, flint corn-based diets. In this study, 112 Nellore type bulls (initial BW 384.07 ± 29.53 kg and 24-36 mo of age) were individually fed using Calan gates or individual pens. The animals were used in a randomized complete block design in a 2 × 4 factorial arrangement with 2 CPM, high-moisture flint corn (HMC) or finely ground dry flint corn (FGC), with 1 of 4 levels of rNDF, 3, 8, 13, and 18% (DM basis), using sugarcane silage (SS) as roughage. Bulls were adapted to the finishing diet over a 21-d period and fed for a total of 81 d. Fecal starch (FS) concentration was determined on d 46 and 74 of the feeding period. There was a quadratic effect of rNDF on final BW (P < 0.01) and ADG (P = 0.01). Optimal concentrations of rNDF were estimated using the first derivative of second order polynomials, indicating that final BW and ADG were maximized with 13.3 and 13.0% rNDF, respectively. An interaction was observed between CPM and rNDF (P = 0.05) for DMI, with peak DMI occurring at 11.3 and 13.7% rNDF with FGC and HMC, respectively. Cattle fed HMC had 13.9% greater G:F (P < 0.01) compared with those fed FGC (0.172 vs. 0.151, respectively). There were quadratic effects of rNDF on HCW (P = 0.04) and ME intake (P < 0.01); heaviest carcass weights were estimated, in both cases, to be achieved with 12.8% rNDF. A quadratic effect of rNDF for renal, pelvic, and inguinal fat weight (P = 0.04) was observed, with a peak estimated to occur at 12.6% rNDF. An interaction between CPM and rNDF also was observed for FS (P < 0.05). Bulls fed FGC with 3% rNDF had greater FS content, and FS linearly decreased as concentration of rNDF increased. For bulls fed HMC, FS was 3.0% of DM and was unaffected by rNDF in the diet. Lower FS from bulls fed HMC suggests that availability of starch from flint corn was greater than that of FGC. For Nellore-based cattle fed a flint corn-based diet containing SS and 8% whole lint cottonseed, performance was optimized with 12.8% rNDF. In the absence of cottonseed addition to diets, optimal performance would be expected with about 14.5% rNDF.

RESUMO -Este trabalho foi realizado para se avaliar o desempenho animal, as características da carcaça e a maciez da carne de 36 novilhos mestiços, apresentando, ao início do experimento, média de 14 meses de idade e aproximadamente 320 kg de peso vivo. Os animais foram confinados e receberam dietas com alto teor de concentrado: uma controle (CO), sem adição de lipídios; outra contendo 5% de sais de cálcio de ácidos graxos (AG); e outra com 21% de caroço de algodão (CA). A ingestão de matéria seca no tratamento AG foi menor que no CA, mas não diferiu da ingestão do CO. O ganho médio diário e a eficiência alimentar não apresentaram diferenças significativas entre os tratamentos. Os valores encontrados para a análise de uréia sangüínea foram significativamente maiores no tratamento CA em relação ao AG. O rendimento de carcaça, a área de olho de lombo, a espessura de gordura, as gorduras renal e pélvica, o peso do fígado, o pH e a temperatura não foram significativamente diferentes. Não houve diferença também para o índice de perda de água por cozimento e maciez, verificada pela força de cisalhamento nos diferentes tempos de maturação. Os sais de cálcio de ácidos graxos a 5% e o caroço de algodão a 21% podem ser empregados nas rações para confinamento, sem causarem alterações no desempenho animal ou nas características de carcaça.Palavras-chave: características de carcaça, caroço de algodão, confinamento, espessura de gordura, rendimento de carcaça, sais de cálcio de ácidos graxos Performance and Carcass Characteristics of Steers Fed Different Fat SourcesABSTRACT -The objective of this trial was to evaluate the animal performance, carcass characteristics and meat tenderness of 36 crossbred steers averaging 14 months old and 320 kg body weight. The animals were fed high concentrate-based diets: control -without additional fat (CO); diet with 5% calcium salt of fatty acids (AG); and diet with 21% whole cottonseed (CA). Dry matter intake of AG treatment was lower (P=0,05) than CA, that differ from CO diet. No significant differences of treatments on daily weight gain and feed efficiency were observed. Blood urea nitrogen was greater (P=0,01) for CA treatment than AG treatment. Carcass dressing, rib eye area, fat thickness, kidney and pelvic fat, liver weight, pH and temperature did not show significant difference. No difference on water loss during cooking and tenderness measured by shear force at different aging times was detected. Diets with 5% calcium salt of fatty acids or 21% whole cottonseed can be used for feedlot with no change on animal performance or carcass characteristics.

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