Effects of protein content and rumen-undegradable to rumen-degradable protein ratio in finely ground calf starters on growth performance, ruminal and blood parameters, and urinary purine derivatives

This study investigated the effects of feeding finely ground starter diets containing either 18 or 22% crude protein (CP) content [dry matter (DM) basis] and high low ratios rumen-undegradable to rumen-degradable (RUP:RDP) on growth performance, nutrient digestibility, ruminal fermentation, blood metabolites, urinary purine derivatives in dairy calves. A total 48 three-day-old female Holstein calves with 40.2 ± 2.5 kg initial body weight (BW) were randomly assigned a complete randomized block design 2 × factorial arrangement treatments (12 calves/treatment). Treatments as follows: (1) diet (mean particle size = 0.69 mm) 18% CP RUP:RDP ratio [low (LR) 26:74; 18CP-LR]; (2) [high (HR) 35:65; 18CP-HR]; (3) (22CP-LR); (4) (22CP-HR) DM bases. Blocking was based day treatment assignment, within each block. Calves received 4 L milk daily from d 3 10, 7 L/d 11 40, 41 49, 50 53, then all weaned but remained experiment until 83 age. The results showed that overall average gain (ADG), weaning BW, feed efficiency (FE) greater than CP. Increasing did not influence intake, dry intake (DMI), postweaning ADG, FE No effect observed for DMI, preweaning FE, grams per megacalorie metabolizable energy. RUP ADG fed HR those LR diets. digestibility neutral detergent fiber greater, OM tended be concentrations short-chain fatty acids (SCFA), acetate proportion, acetate-to-propionate 2-way interaction between time SCFA, ratio, indicating concentration had more parameters. Preweaning derivatives, microbial synthesis, nitrogen 22CP 18CP affected by different ratios. glucose insulin when compared Therefore, we conclude can have beneficial probably through increased synthesized concentration; however, marginal performance during period.