RESUMO
Corn grain with a high phosphorus (P) content (mainly in the form of phytate-P) may need to be processed to improve the digestibility of nutrients for young calves. Processing corn grains can improve the accessibility of phytate-P to the rumen enzymes and increase the bioavailability of P, which benefits the growth and development of calves. The objective of this study was to investigate the effects of feeding starter diets with steam-flaked corn (SFC) compared with ground corn (GC) with 2 P contents of 0.4% and 0.7% DM basis on intake, growth performance, nutrient digestibility, blood metabolites and urinary purine derivatives in dairy calves. A total of 48 female Holstein dairy calves (3 d old; average initial weight 39.7 ± 3.9 kg) were randomly assigned to a 2 × 2 factorial arrangement of treatments (12 calves/treatment) in a randomized complete block design. The treatment groups were: 1) a starter diet of GC with 0.4% P (GC-0.4P); 2) a starter diet of GC with 0.7% P (GC-0.7P); 3) a starter diet of SFC with 0.4% P (SFC-0.4P); 4) a starter diet of SFC with 0.7% P (SFC-0.7P). Calves received 6 L/d of transition milk on d 2-3 and 5 L/d of whole milk on d 4-30, which was increased to 7 L/d on d 31-45, then decreased to 5 L/d on d 46-60 and reduced to a single feeding of 2 L on d 61-62. All calves had free access to starter feed and water. All calves were weaned on d 63 and remained in the study until d 83. Rumen fluid samples were collected on d 38 (pre-weaning) and d 76 (post-weaning). Blood samples were collected on d 40 and 80 and urine samples were collected on 4 consecutive days from d 79 to 82 to analyze urinary excretion of PD. The phytate-P content ranged from 0.23 to 0.17 for GC and SFC, respectively. In particular, the interaction between corn processing method and P content showed that the SFC-0.7P diets had a greater intake of starter feed during the pre- and post-weaning periods compared with the other experimental groups. In addition, calves fed the SFC-0.7P diet had greater average daily gain, body weight, withers height at weaning, better organic matter digestibility, higher blood ß-hydroxybutyrate levels and higher microbial protein synthesis compared with all other groups. Feeding the SFC diet also resulted in improved feed efficiency, improved P digestibility and a tendency toward a lower rumen pH, albeit with a tendency toward an increase in blood glucose concentration during the pre-weaning period. In addition, the inclusion of 0.7% P to the starter diet resulted in increased fiber digestibility and a slight improvement in growth performance, which was particularly evident in hip height. Overall, the inclusion of SFC in the calf starter diet, especially in combination with a 0.7% DM basis P supplement, improved growth performance and nutrient utilization in dairy calves compared with GC.
