Performance and carcass traits of Nellore cattle fattening on pasture receiving different zinc contents in the mineral supplementation

Objetivou-se estudar o efeito de diferentes teores de Zinco na suplementação mineral de novilhos Nelore em pastagem de Brachiaria brizantha cultivar (cv) MG-4, sobre o desempenho produtivo e características de carcaça. Foram utilizados 28 animais, castrados, com peso vivo médio inicial de 355 kg. Os animais foram divididos ao acaso em quatro grupos e alojados em piquetes de 6,25 hectares cada, equipados com comedouro coberto e bebedouros, sendo pastejados alternadamente a cada pesagem (28 dias). O delineamento experimental foi inteiramente casualizado, com quatro dosagens de zinco (Zn) no suplemento mineral e sete repetições. As doses de zinco avaliadas foram: Zn-0, sem adição de Zinco; Zn-2, com 2.000 mg de Zn kg-1; Zn-4, com 4.000 mg de Zn kg-1; e Zn-6, com 6.000 mg de Zn kg-1; sob forma inorgânica (Sulfato de Zinco) no suplemento mineral. Os suplementos minerais foram pesados e fornecidos ad libitum, em cochos cobertos, com controle das sobras para determinação do consumo. O período experimental foi de 370 dias. De cada animal abatido pesaram-se órgãos, vísceras, carcaça e componentes não carcaça. Avaliaram-se a área de olho de lombo (AOL) e espessura da gordura subcutânea (EGSC), bem como a cor, pH e oxidação lipídica. A crescente inclusão do zinco na dieta dos bovinos, não influenciou (P > 0,05) o peso vivo final (PVF) e o ganho de peso médio diário (GPMD). Observou-se diferença (P 0.05) final body weight (FBW) and average daily weight gain (ADWG). Difference (P < 0.05) was observed in the Zn intake (ZnI) (? = -2.09386 + 146.9616x; R2 = 0.99) and hot carcass weight (?= 299.92662 + 3.33362x; R2= 0.24), as well as, in meat lipid oxidation (? = 0.15170 + 0.02539x; R2= 0.31). There was an increasing linear effect for meat color, evaluated by values of L* (luminosity) (? = 32.23309 + 0.41445x, R2 = 0.14), a* (red-green intensity) (? = 0.88592 + 18.16225x, R2 = 0.25) and b* (yellow-blue intensity) (? = 9.35295 + 0.45030x, R2 = 0.20), but remained within normal values for meat. It can be concluded that beef cattle grazing Brachiaria brizantha MG-4, and supplemented with different zinc contents in mineral supplements, supplied ad libitum, do not show changes in weight gain, carcass yield, physical carcass composition, as well as, in non-carcass components, but the Zn content has a positive linear influence on hot carcass weight, without causing changes in absolute and relative weights of organs and viscera

Prediction models of the nutritional quality of fresh and dry Brachiaria brizantha cv. Piatã grass by near infrared spectroscopy

ABSTRACTThis study aimed to generate prediction models to estimate the chemical composition of fresh and dry Brachiaria brizantha cv. Piatã grass using near infrared spectroscopy (NIRS). Chemical analyses of 249 samples were performed to determine oven-dried sample (ODS), dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose (CEL) and total digestible nutrients (TDN). The samples were scanned in an NIRS spectrometer and different percentages were used to compose and develop the models (100% fresh; 100% dry; 25% fresh:75% dry; 50% fresh:50% dry and 75% fresh:25% dry). The purpose of these mixed models is to know if it is possible to obtain reliable predictions from fresh samples in a database that contains dry samples. The calibration models were developed using modified partial least squares (MPLS) and evaluated by statistical parameters, including coefficient of determination (R²) and residual predictive deviation (RPD). The model with 100% dry samples obtained the best results in R² and RPD validations, for CP (0.94; 3.98), NDF (0.92; 3,49) and TDN (0.90; 3.12). The 100% fresh samples produced the best R² results in ODS (0.83), CP (0.85), ADF (0.84) and ADL (0.83). A screening model was validated to predict the characteristics and components of the fresh samples. The model using 100% dry grass was suitable for predicting all the variables, except ODS, DM and CEL