Idalmo Garcia Pereira

The objective of this work was to evaluate random regression models with linear spline functions for the estimation of genetic parameters of residual feed intake (RFI) in Nellore bovines. The RFI was estimated across five test periods (at 0-14, 0-28, 0-42, 0-56, and 070-days) in 929 Nellore bulls. The variance components were estimated, and the models were compared using the deviance information criterion. Rankings and the percentage of the top 10% animals across all periods were assessed using Spearman’s correlations. The best-fit model included linear splines and heterogeneous residual variance (four classes). Heritability estimates for RFI ranged from 0.39 to 0.55, with high genetic (0.83-0.98) and phenotypic (0.82-0.98) correlations between adjacent periods. Rankings were consistent between 56 and 70 days (Spearman’s correlations = 0.99; 93.55% overlap). The test period can be shortened to 56 days without compromising genetic parameters, optimizing feed intake evaluations. The random regression models effectively model the RFI, showing sufficient genetic variance for selection.

Macadamia oil has high concentrations of oleic and palmitoleic fatty acids, which can increase tissue sensitivity to insulin, improving glucose absorption efficiency, and reducing lipogenesis through gene modulation. The objective of this study was to evaluate the effects of macadamia oil associated with vitamin E supplementation on performance, blood parameters, meat quality and sensory characteristics, meat fatty acid profile, and expression of genes associated with lipid metabolism in grazing lambs. The experimental treatments were control diet (Control), Control + 0.1% of body weight of macadamia oil (MO), MO + 745 IU of vitamin E/dry matter (MOVE). Macadamia oil improved feed efficiency, reflecting a lower dry matter intake, as the average daily weight gain did not differ from Control. Meat quality parameters were not affected by macadamia oil or vitamin E supplementation. Supplementation with macadamia oil improved meat appearance, flavor, and overall liking. Supplementation with macadamia oil provided a higher proportion of C18:3 n3 and a lower proportion of CLA. The expression of SREBP-1c, PPAR-α, SCD1, and ELOVL6 genes were not modified with the supplementation of macadamia oil and vitamin E. In conclusion, supplementation with macadamia oil improves feed efficiency and meat quality; and the inclusion of 745 IU of vitamin E/kg of dry matter for grazing lambs reduces 36% of lipid oxidation of the meat.

The aim of this study was to investigate the effects of feeding systems on the growth performance of Santa Inês x Dorper lambs, meat quality, fatty acid profile, and gene expression. Thirty lambs at an initial body weight of 22.6 ± 2.59 kg were randomly assigned to one of three feed systems: a grazing system with 1.2% body weight concentrate supplementation (GS); a feedlot system with 28% forage and 72% concentrate (FFC); or feedlot with 85% whole corn grain and 15% pellets (FHG). The lambs were slaughtered after 60 days of experiment. Average daily gain, glucose, and insulin concentration were higher for lambs on FHC than lambs on a GS feeding system. The fatty acid profile in the meat of the lambs fed GS showed a higher proportion of c9t11-C18:2, C20:5, C22:5, and C22:6 compared with FFC and FHC (p < 0.05). Meat tenderness was lower for lambs under FFC treatment compared with GS and FHG. FHG treatment provides better performance and higher deposition of lipid content in meat compared with GS and FHG. The expression of the genes SCD-1, SREBP1-c, and EVOL6 was greater in lambs undergoing GS and FHC treatments compared with FFC. Results of this research showed a reduced performance of grazing lambs compared with the feedlot system; however, it enhanced the fatty acid profile with increased levels of polyunsaturated acids and reduced n6/n3 ratio.

Objective: The aim of this study was to identify suitable polynomial regression for modeling the average growth trajectory and to estimate the relative development of the rib eye area, scrotal circumference, and morphometric measurements of Guzerat young bulls.Methods: A total of 45 recently weaned males, aged 325.8±28.0 days and weighing 219.9±38.05 kg, were evaluated. The animals were kept on Brachiaria brizantha pastures, received multiple supplementations, and were managed under uniform conditions for 294 days, with evaluations conducted every 56 days. The average growth trajectory was adjusted using ordinary polynomials, Legendre polynomials, and quadratic B-splines. The coefficient of determination, mean absolute deviation, mean square error, the value of the restricted likelihood function, Akaike information criteria, and consistent Akaike information criteria were applied to assess the quality of the fits. For the study of allometric growth, the power model was applied.Results: Ordinary polynomial and Legendre polynomial models of the fifth order provided the best fits. B-splines yielded the best fits in comparing models with the same number of parameters. Based on the restricted likelihood function, Akaike's information criterion, and consistent Akaike's information criterion, the B-splines model with six intervals described the growth trajectory of evaluated animals more smoothly and consistently. In the study of allometric growth, the evaluated traits exhibited negative heterogeneity (b<1) relative to the animals' weight (p<0.01), indicating the precocity of Guzerat cattle for weight gain on pasture.Conclusion: Complementary studies of growth trajectory and allometry can help identify when an animal's weight changes and thus assist in decision-making regarding management practices, nutritional requirements, and genetic selection strategies to optimize growth and animal performance.

The objectives were to conduct a genetic evaluation of residual feed intake (RFI) and residual feed intake adjusted for fat (RFIFat) and to analyse the effect of selection for these traits on growth, carcass and reproductive traits. Data from 945 Nellore bulls in seven feed efficiency tests in a feedlot were analysed. Genetic evaluation was performed using an animal model in which the feed efficiency test and age of the animal at the beginning of the test were considered as a systematic effect. Direct additive genetic and residual effects were considered as random effects. Correlations and genetic gains were estimated by two‐trait analysis between feed efficiency measures (RFI and RFIFat) and other traits. Feed conversion showed low heritability (0.06), but dry matter intake (DMI), average daily gain, RFI, RFIFat, metabolic body weight and scrotal circumference measured at 450 days of age (SC450) showed moderate to high heritability (0.49, 0.28, 0.33, 0.36, 0.38 and 0.80, respectively). Similarly, ribeye area, backfat thickness, rump cap fat thickness, marbling score and subcutaneous fat thickness also had high heritability values (0.46, 0.37, 0.57, 0.51 and 0.47, respectively). Genetic correlations between RFI and SC450 were null, and between RFIFat and SC450 were strongly positive. Genetic and phenotypic correlations of RFI and RFIFat with carcass traits were not different from zero, as correlated responses for carcass traits were also not different from zero. The Nellore selection for feed efficiency by RFI or RFIFat allows the recognition of feed efficient animals, with DMI reduction and without significant changes in growth and carcass traits. However, because of the observed results between RFIFat and SC450, selection of animals should be analysed with caution and a preselection for reproductive traits is necessary to avoid reproductive impairments in the herd.

The objective of this study was to apply data transformation via isotonic regression in growth curves studies of Guzerá cattle whose data presented disturbances characterized by decreased body weight in certain age groups. Weight-age data were collected on newly weaned Guzerá males according to the methodology of weight gain tests (WGT) defined by the Brazilian Association of Zebu Breeders (ABCZ). The Logistic, Von Bertalanffy and Gompertz models were fitted to weight-age data using the generalized least squares method for non-linear regression models through the Gauss-Newton algorithm. The proposed transformation based on isotonic regression theory proved to be efficient; and the Logistic model was the best to describe the growth of animals, with a high percentage of convergence (100%) and goodness of fit assessed by the mean squared error (MSE) and the coefficient of determination (R²).

The objective of this study was to evaluate residual feed intake (RFI), residual intake and body weight gain (RIG) and their relationship with other traits of efficiency, performance, and economic analysis of sheep. Lambs (n = 102) were evaluated during 56 days and a herd consisting of 500 ewes was simulated with the mean of dry matter intake (DMI) and final body weight of the lambs, the same as that of the experimental lambs. The lambs were fed hay-based diet of Tifton 85 (Cynodon spp.), corn, and soybean in the voluminous:concentrate ratio of 35:65. Residual feed intake and RIG were correlated with DMI, feed conversion ratio, and feed efficiency. Residual intake and body weight gain were positively correlated with average daily gain, relative growth rate, and Kleiber's rate. The most efficient production systems (lower RFI and higher RIG) had lower costs and higher profit margins. The net present value (NPV) and internal rate of return (IRR) were higher in systems with more efficient lambs. In systems with less efficient lambs, NPV and IRR were negative and lower, respectively. Efficient animals for RFI and RIG showed satisfactory performance and better economic results.

Our objective was to estimate genetic parameters, and genetic and phenotypic trends for bodyweight (BW; measured at birth, 120, 205 (weaning age), 365, 450 and 550 days of age), scrotal circumference, and visual appraisal scores of body conformation in Guzerat cattle. Data regarding body structure, finishing precocity, muscling, sheath and navel, breed characteristics, limbs (soundness of feet and legs), and sexuality, which were visually appraised, were obtained from the Brazilian Association of Zebu Breeders, recorded between 1970 and 2013 in five Brazilian states. Variance components and heritability were estimated by using linear animal (for continuous variables) and threshold (for categorical variables) models using Bayesian inference. Genetic and phenotypic trends were obtained by regressing the average annual genetic value relative to animal’s birth year. The direct heritability values for BW were high, ranging from 0.38 to 0.45, whereas the maternal effect was responsible for 17–23% of the phenotypic variation. For scrotal circumference, the direct heritability values were median with values ranging from 0.08 and 0.15, whereas for visual appraisal scores, the values were median to high (0.07–0.18). Higher response to selection for BW traits is expected for those with moderate to high heritabilities. The estimated genetic trends indicated favourable changes for BW with average annual changes of 396, 2948, 3388, 5808, 8184, and 8096 g for BW at the respective ages. The genetic values were decreasing over the years for scrotal circumference, body structure, finishing precocity, muscling, and sheath and navel. Therefore, a longer evaluation period should be utilised to assess these traits as little time has elapsed from the beginning of the selection until the time of the present study.

The study of the genetic evaluation of residual feed intake adjusted for fat (RFIFat) is important for the appropriate use of feed efficiency in selection programs. The objective was to analyze the influence of selection for RFIF at on carcass and performance traits by estimating various genetic parameters. Data were analyzed from five tests of feed efficiency, which were conducted with 677 Nellore males. Genetic evaluation was performed by Bayesian inference using an animal model via single- and two-trait analyses. Variables analyzed were dry matter intake, average daily gain, RFIFat, rib eye area, back fat thickness, rump fat thickness, marbling score, and subcutaneous fat thickness. The posterior mean distributions estimated at each analysis were used to estimate heritability of the traits and to perform various correlations. The studied traits showed high heritability estimates, and they should respond well to selection. The RFIFat presented a phenotypic correlation with carcass traits (which was next to zero), and there was also a negative genetic correlation. Additive genetic variability for RFIFat showed that selection for this trait can promote genetic gains in future generations, resulting in animals that are efficient in terms of nutrient use, and according to the genetic and phenotypic correlations, with no significant negative changes to carcass traits.