Equations to predict calf starter intake (SI) were developed and evaluated using individual animal data from studies carried out at the University of Illinois (UI: 1973 observations from 448 calves, initial BW = 42 ± 4.4 kg) and University of São Paulo (USP: 3050 observations from 527 calves, initial BW = 37 ± 5.4 kg). Each data set was randomly divided into 2 subsets (60% for development, 40% for evaluation). The mixed model for weekly repeated measures included the random effect of study. The autoregressive covariance structure (AR1) was adopted in the model. Body weight (BW, kg), daily metabolizable energy intake from the liquid diet (MEiLD, Mcal/d), average daily gain (ADG, g/d) and time relative to first offer of starter (FPstarter, wk) were used as independent variables. The mean square error of prediction (MSEP), mean bias, concordance correlation coefficient (CCC), and analysis of linear regression were used to select models. The UI calves were fed greater amounts of milk replacer than Brazilian calves (761 vs 574 g/d). Models showed a better accuracy after 3 wk of voluntary SI. The model for UI data explained about 65% of the variation in observed SI with a mean bias of –86 g/d, while the model for USP data accounted for 59% with a mean bias of –47 g/d (Table 1). Both models, however, accurately predicted the SI (Cb >0.90). The lower precision of model for USP data is likely because of differences in genetics, management, and environmental variables. These empirical models can provide guidelines for SI of young calves, but additional models might be needed to further improve the predictability of SI. Table 1.

Variable	Temperate conditions			Tropical conditions
Observed(n= 789)	US model1	Observed(n= 1220)	Brazilian model2
Starter DMI (g/d)	544	630		371	418
Mean bias (Y – X, g/d)	—	−86
MSEP (g × g)	—	132,823
CCC	—	0.75
Cb	—	0.93
r	—	0.81
r2	—	0.65

¹Starter DMI (g/d) = [(23.6928 × BW) + (−198.77 × MEiLD) + (0.06441 × ADG) + (61.9202 × FPstarter) − 430.40]. ²Starter DMI (g/d) = [(14.0273 × BW) + (743.11 × MEiLD) + (−149.24 × MEiLD²) + (0.2696 × ADG) + (−0.00007 × ADG²) + (−32.5774 × FPstarter) + (14.1437 × FPstarter ²) − 1640.72].