The Small Ruminant Nutrition System: Considering the ruminal fiber stratification for goats

Abstract Text: The objective of this research was to assess the ability of a mechanistic model named Small Ruminant Nutrition System (SRNS) to predict the metabolizable energy intake (MEI) and milk yield (MY) by using a heterogeneous ruminal fiber pool scenario (GnG1; Regadas Filho et al., 2014) in comparison to a traditional homogeneous scenario (G1), The GnG1 scenario considers that the first ruminal fiber pool (raft) follows an age-dependent fractional rate for particle transference from a raft to an escapable pool (λ_r) and that the second ruminal fiber pool (escapable) follows an age-independent fractional rate of particle escape from the escapable pool (k_e); for G1, a scenario with only a single fractional rate passage (k_p) is adopted. All parameters were estimated individually by using equations published in the literature; however, for the G1 scenario, two rate passage equations were used, with one from sheep data (G1-S; Cannas et al., 2004) and another from goat data (G1-G; Tedeschi et al., 2012). The MEI, MY and DMI estimated by using these scenarios were compared with the results of an independent dataset (n = 327) that contained information regarding the DMI, MEI, MY, BW and milk and dietary compositions. The evaluation of the scenarios was performed using a coefficient of determination (r²) between the observed and predicted values; mean bias (MB); bias correction factor (C_b) and concordance correlation coefficient (CCC). The MEI estimated by the GnG1 scenario yielded a precision and accuracy (r² = 0.82; MB = 0.21 Mcal.day^-1; C_b = 0.98) similar to that of the G1-S (r² = 0.85; MB = 0.10 Mcal.day^-1; C_b = 0.99) and G1-G (r² = 0.84; MB = 0.18 Mcal.day^-1; C_b = 0.98) scenarios. The results were also similar for the MY; however, a significant MB (P<0.01) was found as follows: GnG1 (r² = 0.74; MB = 0.70 kg.day^-1; C_b = 0.79), G1-S (r² = 0.71; MB = 0.58 kg.day^-1; C_b = 0.85) and G1-G (r² = 0.71; MB = 0.65 kg.day^-1; C_b= 0.82). The GnG1 scenario can be assumed to maintain the theoretical basis of mechanistic models. 

Keywords: fiber stratification, goat, heterogeneous fiber pool