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1535
The net macromineral (Ca, P, Mg, Na, and K) requirements for growth in beef cattle estimated by meta-analysis
To predict mineral requirements in beef cattle, the factorial method has been the most utilized. A meta-analysis was utilized to estimate the net macromineral (Ca, P, Mg, Na, and K) requirements for growth in Nellore cattle. A database composed by 873 animals from 21 studies conducted in tropical conditions was developed, being 411 bulls, 255 steers, and 157 heifers. Also, animals were from the following genetic groups: Nellore (n=473), Zebu × Holstein (n=149), and beef crossbred cattle × Nellore (n=250). The net mineral requirement was calculated using the following allometric model: Mi = a × EBWb, which Mi is the amount of each mineral in the body, EBW is the empty body weight, and a and b are parameters of the model. When differences were observed for sex (bulls, steers, and heifers) and genetic group (Zebu, dairy crossbred, and beef crossbred cattle), distinct equations were generated separately. For crossbreeding, differences between dairy crossbred and beef crossbred were not verified (P>0.05) for any mineral, which allowed us to analyze genetic group such as Zebu and crossbred cattle. Moreover, the allometric plateau method was utilized to reach the empty body weight which animals achieve maturity for mineral retention and, after this point, there is only mineral requirements for maintenance. Thus, differences regarding to sex were observed for Ca and Na allowing us to generate different equations for bulls, steers and heifers. Also, from database utilized in this study, bulls stablish their need for Ca and Na when reach 432 and 424 kg of EBW, respectively; while for steers the EBW to reach maturity of these minerals were 421 and 481 kg, respectively. For heifers, the EBW was 432 and 405 kg for Ca and Na, respectively. In the case of P, Mg, and K, differences were verified for genetic group where zebu cattle establish the need of P, Mg, and K for growth when the EBW is 522, 427, and 460 kg, respectively. Moreover, considering crossbred cattle, the estimate of EBW for reach maturity of P, Mg, and K is 469, 433, and 492 kg, respectively. Therefore, we believe that the equations for the net macromineral requirement for growth can improve the understanding of dietary mineral requirements of beef cattle and contribute to correct supply of minerals in diet reducing losses and environment pollution.
Keywords:
beef cattle, mineral, requirement