Incremental nicotinic acid supplementation to preweaning dairy calves: Effects on growth, blood metabolites, purine derivatives, and indirect rumen development.

This experiment investigated nicotinic acid (NA) supplementation on growth, plasma glucose (GLU) and ketone concentrations, and urinary purine derivative (PD) excretion as indicators of ruminal development. Forty (22 male, 18 female) Holstein dairy calves, with initial body weight of 42.5 ± 5.60 kg (mean ± SD), were blocked by birth and randomly assigned to 1 of 4 levels of NA added to calf starter: 0 g/d (CON), 2 g/d (2NA), 4 g/d (4NA), and 6 g/d (6NA). Following parturition, calves received 4 L of colostrum (>50 g IgG/L) within 24 h of birth and entered the study 1 d after birth until d 56. Calves had ad libitum access to water and starter (22.48 ± 0.83% CP). Calves were fed 3 L of milk replacer (MR; 24% protein, 17% fat) twice daily from d 2 to 42 (milk phase). Weaning started on d 43 to 49, with calves fed 3 L of MR every morning (weaning phase). Postweaning (d 50-56) calves were not fed MR. Body weight, withers and hip heights, length, and heart girth were measured on d 2 and weekly until d 56. Blood samples were taken at 24 h for IgG analysis and on d 2 of age and weekly until d 56 for GLU and ketone analyses. Urine samples were collected at 2 h and 4 h after feeding on d 56. Orthogonal polynomial contrasts were used to test the linear, quadratic, and cubic effects of incremental NA supply. Supplementing NA resulted in a linear reduction in starter intake and DMI during the milk phase and a tendency for a linear decrease after weaning. A tendency for improved feed efficiency (FE; ADG/DMI) was observed to increase linearly in the milk phase but remained unaffected thereafter. No treatment effects were observed for milk replacer intake or ADG during the milk and weaning phases; however, ADG exhibited a quadratic response in the postweaning phase. Water intake followed a quadratic response during the milk and weaning phases but was similar after weaning. Nicotinic acid intake displayed linear and cubic responses across all phases, with a treatment × week interaction. Weekly and final withers height and withers height gain demonstrated quadratic responses to increasing NA, with the greatest values in calves receiving 2NA. Similar patterns were seen in weekly hip height, final hip height, and final heart girth. Other skeletal measurements, including weekly length and weekly heart girth, were not affected by NA supplementation. Ketone concentrations showed no treatment effects except for a cubic tendency in final concentrations. Weekly GLU levels exhibited a negative linear tendency across treatments. Urinary creatinine and uric acid concentrations were unaffected. Allantoin and PD excretion increased linearly and showed a cubic tendency, with the greatest values at 2NA, indicating enhanced microbial protein synthesis. These findings suggest that 2NA supplementation improves FE, skeletal growth, and markers of rumen development (blood ketone and GLU concentrations). Greater doses of NA had no adverse effects, and calves receiving 2NA showed greater growth performance and indicators of rumen development, suggesting the potential benefits of moderate NA supplementation preweaning.