Date of Award

Spring 2020

Project Type

Dissertation

Program or Major

Biological Sciences

Degree Name

Doctor of Philosophy

First Advisor

André F Brito

Second Advisor

Peter S Erickson

Third Advisor

Paul J Kononoff

Abstract

Lactating dairy cows are characterized by poor N efficiency and dietary N not captured in milk protein is excreted in urine and feces, which then contribute to environmental N pollution. Nitrogen losses also shrink profit margins for dairy producers due to costly protein sources. Additionally, the dairy industry is an important anthropogenic source of greenhouse gases such as CO2 and CH4, with CH4 representing a potent greenhouse gas and non-negligible energy losses in dairy cattle. Thus, my PhD program has focused on developing nutrition-based approaches to improve milk production efficiency (e.g., milk yield/dry matter intake) and reduce N excretion and greenhouse gas emissions from dairy cattle. Three experiments were conducted on lactating Holstein cows to investigate the effects of rumen protected AA and levels and sources of energy on milk production and nutrient utilization in dairy cows fed low protein diets. Dairy rations with high energy (≥ 1.60 Mcal of net energy of lactation/kg) and low protein (≤ 16% crude protein) concentrations have been shown to increase milk production and feed efficiency and decrease urinary N excretion and CH4 emissions. We also discovered that feeding low protein dairy diets (≤ 16% crude protein) with fibrous byproducts and RP-fat as replacements for ground corn further enhanced milk production efficiency and milk fat yield without contributing more CO2 and CH4 to the environment. Furthermore, supplementation with rumen-protected Met, Lys, and His had limited effects on milk production and nutrient utilization in dairy cows fed low protein diets. These findings mean that farmers may feed cows diets high in fat and low in protein to achieve gains in profit margin and production efficiency. Further research is still needed to compare high protein (≥ 17% crude protein) diets and high fat, low protein diets on production performance and balance of N and energy in lactating dairy cows.

Available for download on Saturday, June 19, 2021

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