Net macromineral requirements for gain of Saanen goats

The objective of this study was to evaluate the effect of sex on the net Ca (NCa_G), P (NP_G), Mg (NMg_G), Na (NNa_G), and K (NK_G) requirements for gain of Saanen goats from 5 to 45 kg BW. For this purpose, a database with 226 individual records (76 intact males, 71 females, and 79 castrated males), was gathered from six comparative slaughter experiments. Total Ca, P, Mg, Na, and K in the body were fitted to a logarithmized allometric equation using the mixed model procedure. Sex was considered as fixed effect, and study and residual error were considered random effects. The net requirements for gain (NCa_G, NP_G, NMg_G, NNa_G, and NK_G) were estimated by the first partial derivative of the logarithmized allometric equation with respect to empty BW (EBW). The standard deviations of estimated NCa_G, NP_G, NMg_G, NNa_G, and NK_G were calculated using the Monte-Carlo simulation. Sex did not affect the Ca, P, Na, and K body composition (P>0.10), and consequently did not affect the NCa_G, NP_G, NNa_G, and NK_G, from 5 to 45 kg BW. The body composition (g/kg EBW) ranged from 9.66 to 9.60 for Ca, 7.77 to 7.74 for P, 1.62 to 1.09 for Na, and 1.94 to 1.42 for K, when BW increased from 5 to 45 kg. The estimated NCa_G (9.59 ? 0.387 g/kg EWG) and NP_G (7.75 ? 0.384 g/kg EWG) remained constant from 5 to 45 kg BW. On the other hand, the estimated NNa_G decreased from 1.33 ? 0.157 to 0.90 ? 0.132 g/kg EWG and NK_G decreased from 1.66 ? 0.132 to 1.21 ? 0.142 g/kg EWG. Sex affected the Mg body composition (P=0.054), and consequently the NMg_G was affected by sex as goats grew from 5 to 45 kg BW. The Mg body composition (g/kg EBW) ranged from 0.48 to 0.45 for females, 0.46 to 0.53 for intact males, and 0.44 to 0.47 for castrated males, when BW increased from 5 to 45 kg. The estimated NMg_G for castrated males (0.482 ? 0.0699 g/kg EWG) and females (0.439 ? 0.0258 g/kg EWG), did not change as BW increased from 5 to 45 kg. On the other hand, for intact males, the estimated NMg_G increased from 0.499 ? 0.0762 to 0.575 ? 0.0939 g/kg EWG, as BW increased from 5 to 45 kg. In conclusion, sex does not affect NCa_G, NP_G, NNa_G, and NK_G of Saanen goats from 5 to 45 kg BW, however intact males showed greater NMg_G than castrated males and females (FAPESP project number - 2014/14734-9).