Author: Rodrigo Alfonso Molano Torres

Publisher:

Published: 2020

Total Pages: 238

ISBN-13:

Dairy cattle replacement programs should provide management and nutrition that best supports the evolving needs of the developing heifer during all phases of rearing. The work described in this dissertation had two main objectives, i) to evaluate the supplementation of nutrients that could be limiting for dairy calves transitioning from the preruminant to the ruminant state, and ii) to quantify energy and protein requirements of the growing dairy animal. The first objective was addressed with two feeding trials evaluating what are considered limiting nutrients during the weaning phase. The first study tested the inclusion of different forms of methionine (Met), one rumen-protected and two different analogs (HMBTa and HMBi), in the calf starter. Calves fed the starter with HMBi consumed more feed postweaning and where heavier at the end of the study, but overall calves seemed not to be limited by Met. The second feeding trial assessed the effect of the combined supplementation of B-vitamins and choline on measures of performance and vitamin adequacy, and results suggested that dairy calves could obtain sufficient B-vitamins and choline from the diet and rumen synthesis to support growth rates over 1 kg/d. For the second objective, a database was constructed by merging eight comparative slaughter studies conducted on growing dairy cattle. Using this data set as input, a first analysis explored different aspects concerning nutritional energetics and generated new maintenance requirements coefficients, estimates of efficiency of ME utilization and predictive equations for energy retention for preruminant and ruminant dairy cattle. A variable efficiency of ME utilization for growth calculated as a function of feeding level offered the best prediction ability of energy retention. Finally, a subsequent analysis generated a system of equations to predict net requirements, true supply and efficiencies of use of N and AA for young preruminant dairy calves. Requirements were defined based on the supply of N and AA per Mcal from total ME and carbohydrate ME. A combined variable efficiency allowed the best prediction of N and AA balance on a net basis. Together both models improved the understanding on nutrient partitioning and enhanced the accuracy to predict nutrient requirements and utilization in growing dairy cattle.