A total of 104,135 test-day records from 13,314 first lactations of daily Gyr x Holstein cows were used. Test-day yields of milk, fat and protein were analyzed using a three-trait random regression model. Heritabilities for daily milk, fat and protein yield ranged from 0.12 to 0.24, 0.13 to 0.21 and 0.12 to 0.26, respectively. For daily yields, the additive genetic correlations ranged from 0.38 to 0.99 (milk), 0.25 to 0.99 (fat) and 022 to 0.99 (protein) and were higher among adjacent test days, decreasing gradually with increasing distance between days of lactation. The additive genetic correlations between the traits at different stages of lactation were high (always > 0.70). The heritabilities for cumulative yield and persistency were 0.21 and 0.14 (milk), 024 and 0.16 (fat) and 0.20 and 0.18 (protein), respectively. The additive genetic correlations for cumulative yield were 0.96 (milk-fat), 0.93 (milk-protein) and 0.90 (fat-protein), and those for persistency were 0.73 (milk-fat), 0.85 (milk-protein) and 0.87 (fat-protein). The correlations between cumulative yield and persistency were negative, but low, for the three traits studied. The random regression model proposed in this study can be applied to the genetic evaluation of dairy Gyr (Bos indiais) cattle using test-day yields rather than the traditional estimates of cumulative yield. (C) 2013 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)