Effects of corn grain processing method in starter ration and weaning strategy on performance, nutrient digestion, rumen fermentation, and blood metabolites of Holstein calves

Abstract

This research explored how corn processing methods and weaning protocols interact and impact calf performance, digestibility, ruminal fermentation, and blood metabolites. Forty-eight 3-day-old Holstein calves (24 females and 24 males; body weight = 38.2 ± 1.56 kg) were allocated to one of the four treatment groups using a 2 × 2 factorial design. The physical form of corn grain [steam-flaked corn (SFC) or ground corn (GC)] and weaning protocol [abrupt weaning (AW) or gradual weaning (GW)] were the experimental factors and resulted in the following treatments: 1) a starter diet containing SFC + AW protocol (SFC/AW), 2) a starter diet containing SFC + GW protocol (SFC/GW), 3) a starter diet containing GC + AW protocol (GC/AW), and 4) a starter diet containing GC + GW protocol (GC/GW). The starter feeds had similar feed ingredients (50.4% corn grain, 35.1% soybean meal, plus 5% chopped wheat straw) and were different only in the physical form of corn grain (SFC vs. GC). In the AW protocol, calves were given 4 L of milk/d from days 3 to 15, then increased to 7 L/d from days 16 to 67. Weaning occurred abruptly from days 68 to 69 by decreasing milk to 3.5 L/day. In the GW protocol, calves received 4 L of milk/day from days 3 to 15, followed by 7 L/day from days 16 to 59. Weaning occurred gradually from days 60 to 69, with this reduction schedule: 6 L/d from days 60–61, 5 L/d from days 62–63, 4 L/d from days 64–65, 3 L/d from days 66–67, 2 L/d on day 68, and 1 L/d on day 69. Total starter intake (d 1 to 90) remained unaffected by the corn grain processing method, but weaning strategy and corn processing method interacted for starter feed intake, as the greatest intake was observed in calves assigned in SFC/GW treatment. Feeding a starter diet containing SFC rather than GC increased DM and NDF digestion. Calves that were fed an SFC-based starter diet grew faster than calves fed a GC-based starter diet. The average daily gain (from d 1 and 90) was greater in calves assigned to GW vs. AW protocol. Calves fed an SFC-based starter feed and assigned to AW protocol converted nutrients toward growth more efficiently throughout the experiment (d 1 to 90). Feeding a GC- vs. SFC-based starter feed resulted in greater rumen ammonia-N concentration. Ruminal pH on day 80 was greater in calves weaned gradually compared to those weaned abruptly. Calves fed GC- vs. SFC-based starter diet had higher blood urea-N and β-hydroxybutyrate concentrations on day 60. Overall, an SFC- vs. GC-based starter feed (containing 5% chopped wheat straw) promoted faster calf growth and improved nutrient utilization. Feeding an SFC-based starter diet in combination with GW protocol resulted in the greatest starter feed intake.