RESUMEN
To evaluate the optimum age of straw addition to starter diet on growth of calves, 40 Holstein calves (36.7 ± 4.96 kg) were assigned at 3 days of age to 1 of 4 treatments in a completely randomized design. Dietary treatments (% of dry matter) were as follows: control starter without any wheat straw (WS) inclusion until weaning (WS0); 90% calf starter concentrate (CSC) + 10% chopped WS offered from day 3 of age to weaning (WS3); 90% CSC + 10% chopped WS offered from day 21 of age to weaning (WS21); and 90% CSC + 10% chopped WS offered from day 40 of age to weaning (WS40). After weaning at 60 days of age, all calves received the same diet until finished at day 72 of age. Solid feed intake was affected by treatments whereby either pre- or post-weaning starter intake was greater for calves fed WS (P < 0.01), and WS3 fed calves had lower starter intake compared to WS21 and WS40 (P < 0.01). Weaning weight was the greatest for WS21 treatment compared to other groups (P < 0.01), although all forage fed calves were heavier than WS0 (P < 0.01). Accordingly, average daily gain also showed a similar pattern (P < 0.01). Without any difference at post-weaning, pre-weaning glucose was lowest in WS0 calves (P < 0.01). There were no effects of treatment on number of days that calves experienced a negative health criterion. In conclusion, we concluded that WS inclusion at d 21 of age is recommendable based on weaning and final BW.