Date of Award

Winter 2024

Project Type

Thesis

Program or Major

Agricultural Sciences

Degree Name

Master of Science

First Advisor

Peter PSE S. Erickson

Second Advisor

Andre AFB F. Brito

Third Advisor

Sarah SA Allen

Abstract

The purpose of this experiment was to investigate the dose response of nicotinic acid (NA) on body growth, blood glucose and β-hydroxybutyrate (BHBA) concentrations, and urinary purine derivatives (PD) excretion in preweaned dairy calves. A total of 40 (22 male and 18 female) Holstein dairy calves averaging initial body weight 42.5 ± 5.60 kg (mean ± SD) were blocked by birth and randomly assigned to 1 of 4 levels of NA: (1) 0 g/d (CON), (2) 2 g/d (2NA), (3) 4 g/d (4NA), and (4) 6 g/d (6NA). Following parturition, calves were separated immediately from their dams before suckling and received 4 L of colostrum (>50 g IgG/L) within 24 h of birth. Calves entered the study one day after birth and remained in the study until 8 weeks (56 d) of age. All the calves had ad libitum access to water and starter (22.48  0.83% CP) from the beginning of the study. Three liters of milk replacer (MR; 24% protein, 17% fat) was fed twice daily in the morning and afternoon. A step-down weaning process was followed starting at 6 weeks of age. Body weight (BW), skeletal measurements (i.e., withers height, body length, hip height, heart girth), and blood samples were taken initially on d 2 of age and continued weekly until weaning on d 56. Blood samples were analyzed for the concentration of glucose, BHBA, and 24 h serum IgG. Urine samples were collected from each calf after 2 h and 4 h of 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 in the post-weaning phase. Feed efficiency (ADG/DMI) tended 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 post-weaning phase. Water intake also followed a quadratic response during the milk and weaning phases but showed no effects post-weaning. Nicotinic acid intake (g/d) displayed linear and cubic responses across all phases, with significant treatment × week interactions. Weekly and final withers height, as well as withers height gain, demonstrated quadratic responses to increasing NA, with the highest values observed 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. β-hydroxybutyrate concentrations showed no treatment effects except for a cubic tendency. Weekly glucose levels exhibited a negative linear tendency across treatments, while urinary creatinine and uric acid concentrations were unaffected. However, allantoin and PD excretion increased linearly and showed a cubic tendency, with the highest values at 2NA, suggesting enhanced microbial growth and microbial protein synthesis. These findings demonstrate that 2NA supplementation improves feed efficiency, skeletal growth, microbial protein production and ruminal development, while greater doses of NA may have diminishing or adverse effects, emphasizing the potential benefits of moderate 2NA supplementation for optimal growth and rumen development during the preweaning phase.Keywords: Growth, nicotinic acid, preweaned dairy calves, purine derivatives

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