Some abstracts do not have video files because ASAS was denied recording rights.
1531
A meta-analysis to estimate the net macromineral (Ca, P, Mg, Na, and K) requirements for maintenance in beef cattle
To predict mineral requirements for 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 maintenance and retention coefficient in Nellore cattle. A database composed by 278 animals from 8 studies conducted in tropical conditions was developed, being 134 bulls, 73 steers, and 71 heifers. Also, animals were from the following genetic groups: Nellore (n=196), Zebu x Holstein (n=46), Angus x Nellore (n=18), and Simmental x Nellore (n=18). Variables such as mineral intake, mineral excretion as feces and urine were collected where retained mineral was calculated by difference between mineral intake and mineral excretion. Thus, the linear regression between retained mineral and mineral intake, as mg/kg BW, was performed to achieve the net mineral requirement for maintenance and retention coefficient where the intercept and slope were considered as the net requirement for maintenance (NRM) and retention coefficient (RC) of each mineral, respectively. Then, the NRM for Ca, Na, and K were 9.85, 4.47, and 16.28 mg/kg BW being these values below than those recommended by the Beef cattle NRC system of 15.4, 15.0, and 38 mg/kg BW. Considering a 300-kg animal, the NRM for Ca would be 2.95 and 4.62 g/d when estimated by this new proposal and the Beef cattle NRC system. This shows that the Ca supply to meet endogenous losses is overestimated which could reduce Ca excretion via feces to environment. Moreover, the NRM for P and Mg were 19.0 and 1.87 mg/kg BW that are close to the recommendations of Beef cattle NRC system of 16.0 and 3.0 mg/kg BW. However, the RC for Ca, P, and Mg were 59.1, 79.6, and 23.5%, respectively that are close to the recommendations of the Beef cattle NRC system of 50, 68, and 17% while the RC for Na and K were 34.2, and 48.8% that are below than those recommend by the Beef cattle NRC system of 91 and 100%. Therefore, we believe that these values for the net macromineral requirement for maintenance and retention coefficient can improve the understanding of dietary mineral requirements of beef cattle.
Keywords: meta-analysis, mineral requirements, Nellore