Performance of Bos indicus beef cattle supplemented with mineral or with concentrates in tropical Urochloa decumbens pastures: A meta-regression approach

Abstract

Models are useful to predict responses of beef cattle to supplementation and its interactions with pasture quality. Therefore, this study was conducted to quantitatively understand variables that influence the performance of cattle under grazing, with or without supplementation, in the tropics by using a meta-analytical approach. The database was composed of individual data of 577 heifers and 194 young bulls from 18 experiments. Information collected included: sex (male or female), total dry matter intake, supplement dry matter intake, forage crude protein (CPforage), forage indigestible neutral detergent fiber (iNDFforage), forage neutral detergent fiber, neutral detergent insoluble protein, crude protein intake from supplement (CPIsupp), metabolizable energy intake from supplement (MEIsupp), initial body weight (BW), final BW and average daily gain (ADG). Additionally, the intakes of rumen degradable protein (RDP), rumen undegradable protein (RUP), and metabolizable protein (MP) from the supplement of each study were calculated. To model animal performance, values within each experiment were divided into two components: ADG-pasture (ADG of non-supplemented animals) and ADG-supplement (differential ADG in relation to non-supplemented animals). Data were evaluated using a meta-analysis approach to estimate fixed and random effects of experiment using linear and nonlinear mixed models. There was no correlation between ADG-pasture and initial BW or final BW. The CPforage was positively correlated, and iNDFforage was negatively correlated with ADG-pasture. Therefore, two equations were developed to predict ADG-pasture, as follows: ADG-pasturemales (kg/day) = 0.007434 × CPforage – 0.001044 × iNDFforage; ADG-pasturefemales (kg/day) = 0.01445 × CPforage – 0.0000642 × CPforage2 – 0.001598 × iNDFforage. There was no correlation between ADG-supplement and total dry matter intake, initial BW, or final BW. The ADG-supplement was positively correlated with CPIsupp and MEIsupp. An exponential model was chosen to fit ADG-supplement. Equations to predict ADG-supplement were composed of three exponential compartments based on ADG-pasture, CPIsupp (or RDP, RUP or MP intakes from supplement), and MEIsupp. The replacement of CPIsupp by RDP, RUP or MP intakes from supplement demonstrated that all protein components could be used to predict the performance of grazing animals. Still, the best fit was observed when RUP intake from supplement was used. The validation process through cross-validation analyses demonstrated that all equations had high accuracy and moderate precision. In conclusion, our results indicate that ADG-pasture can be estimated from CPforage, iNDFforage. The ADG-supplement can be estimated from ADG-pasture, MEIsupp, and protein components intake in grazing heifers and young bulls.