Sex effects on macromineral requirements for growth in Saanen goats: A meta-analysis
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The aim of this study was to investigate the effects of sex on the net requirements of growth for Ca (NCag), P (NPg), Na (NNag), K (NKg), and Mg (NMgg) in Saanen goats from 5 to 45 kg BW, with or without consideration of the degree of maturity. A database containing 209 individual records for Saanen goats (69 castrated males, 71 intact males, and 69 females) was generated from 6 comparative slaughter studies. Total amounts of Ca, P, Na, K, and Mg in the body were fitted to logarithmized allometric equations using empty BW (EBW) or degree of maturity (EBW/mature EBW) as regressors. The equations were fitted using a mixed model, where sex was considered a fixed effect and study was considered a random effect. Net requirements were estimated by the first derivative of the logarithmized allometric equations. Then, a Monte Carlo simulation was used to assess the uncertainty of calculated net requirement values. Without considering the degree of maturity, sex did not affect NCag, NPg, and NNag (P > 0.10). Conversely, considering the degree of maturity, NCag and NPg of intact males were 5% and 2%, respectively, greater than those of castrated males and females (P < 0.01), and NNag of males (castrated and intact) was 6% greater than that of females (P < 0.01). Regardless of approach used, NCag and NPg remained constant, whereas NNag decreased by 32% as BW ranged from 5 to 45 kg. Without considering the degree of maturity, NMgg of castrated and intact males were 8% and 18% greater than that of female goats (P = 0.054), respectively. Hereof NMgg of castrated and intact males increased by 8% and 15%, respectively, whereas that of females decreased by 8% as BW ranged from 5 to 45 kg. Considering the degree of maturity, NMgg of castrated and intact males were 7% and 17% greater than that of female goats (P = 0.054), respectively. In this regard, NMgg of castrated and intact males increased 8% and 16%, respectively, whereas that of females decreased by 7% from 5 to 45 kg BW. Both approaches showed that, regardless of sex (P > 0.10), NKg decreased by 26% (i.e., without considering the maturity degree) or 27% (i.e., considering the degree of maturity) from 5 to 45 kg BW. Therefore, the consideration of maturity stage highlights differences across sexes in the net macromineral requirements for growth in goats. Elucidation of sex effects on macromineral requirements for growth may be useful for improving the accuracy of recommendations for mineral requirements for dairy goats.
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