ABSTRACT The mixed-model methodology is an alternative to select genotypes for traits highly influenced by the environment. In addition, this method allows FOR estimating the repeatability coefficient and predicting the number of assessments needed for a selection process to increase reliability. This study aimed to determine the minimum number of evaluations necessary for a reliable selection process and to estimate the variance components used for predicting genetic gains between and within half-sib families of elephant grass ( Cenchrus purpureus (Schumach.) Morrone ) using the mixed-model methodology. Half-sib families were generated using genotypes from the Active Germplasm Bank of Elephant Grass. The experiment was performed in a randomized block design with nine half-sib families, three replicates, and eight plants per plot. We evaluated 216 genotypes (individual plants) of elephant grass. The deviance analysis was carried out, genetic parameters were estimated, gains between and within families were predicted, and repeatability coefficients were obtained using Selegen software. There was genetic variability for selection within the families evaluated. The reliability values found above 60 % for plant height and number of tillers and above 80 % for dry matter yield suggest that only two evaluations are required to select superior genotypes with outstanding reliability. Sixteen genotypes were identified and selected for their productive potential, which can be used as parents in elephant grass breeding programs for bioenergy production.

ABSTRACT Elephant grass stands out among lignocellulosic biomass plants utilized for second-generation biofuel production due to several advantageous characteristics compared to other raw materials. Its short production cycle and ability to thrive in adverse soil and climate conditions contribute to its appeal. Additionally, breeders seek genotypes with high productivity potential and adaptability to various favorable cultivation environments. This study aimed to estimate genetic parameters, predict genetic values using mixed models (REML/BLUP), and evaluate stability and adaptability for energy biomass production in elephant grass genotypes. The experiment was conducted in Campos dos Goytacazes, RJ, Brazil, utilizing a two-replicate experimental block design that included 40 elephant grass genotypes. Four harvest assessments were performed between 2016 and 2019. Genetic parameter estimation and selection of superior genotypes based on genetic value using the REML/BLUP procedure were performed using Selegen software. Stability and adaptability analyses were obtained through the harmonic mean of genotypic values (HMGV), enabling the identification of stable and highly productive genotypes. Genotypes 17, 18, 32, 16, 36, 6, 15, 31, and 34 exhibited outstanding performance in terms of HMGV, indicating enhanced stability, adaptability, and simultaneous productivity, thus ensuring robustness in cultivation. These selected genotypes hold potential for future breeding programs aimed at improving elephant grass yield for biomass production.

The experiment was carried out with sheep during the finishing phase in a partial confinement system to evaluate the following physiological parameters: rectal temperature (RT), respiratory rate (RR), heart rate (HR), productive performance and carcass characteristics. Fourteen uncastrated sheep with an average initial age of 90 days belonging to two genetic groups were used. There were seven Santa Inês animals, whose average initial live weight (ILW) was 23.65 kg, and seven F1 Dorper × St. Inês animals, with an ILW of 20.02 kg. The treatments were the two genetic groups and two times for the collection of the physiological parameters, at 09.00 h and 15.00 h. Evaluation took place once a week, in a shared stall, always following a 20-min grazing activity. The animals had daily access to a Megathyrsus maximus(Jacquin) pasture, cultivar Masai, from 08.00 h to 17.00 h and their feed was placed in a trough, at a forage:concentrate ratio of 51:49 in the total dry matter. The concentrate consisted of 900 g/kg of ground corn and 100 g/kg of soybean meal, and the roughage supplied was alfalfa hay. There was no interaction between treatments for the studied variables. The physiological parameters were affected only by the time of day. The variables RR and RT were higher at 15.00 h, while the highest HR values were observed at 09.00 h. Neither of the two genetic groups differed for performance and carcass characteristics. Hair sheep belonging to close genetic groups show no differences in performance, carcass characteristics and physiological responses when subjected to heat stress.