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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Dairy Science

First Advisor

David Casper


Three animal feeding studies were conducted with the aim of identifying applicable feeding strategies that will improve nitrogen (N) usage on farm by removing excess protein supplying non-essential amino acids (NEAA), and optimize milking performance of lactating dairy cows through utilization of rumen-protect amino acid (RPAA) products and selection of high-quality rumen-undegradable protein (RUP) sources. Study 1 utilized 16 Holstein dairy cows in a Latin Square design with 28 d periods. Objectives were to evaluate efficacy of low-crude protein (CP) treatment diets formulated with blood meal (LPBM) or rumen-protected lysine (LYS) (LPRPL) as supplemental LYS sources. High-LYS, low-CP diets were compared with a high-LYS, high-CP formulated with soy proteins (HPHL), and a low-LYS, low-CP diet (LPLL). Inclusion of blood meal may have led to decreased dry matter intake (DMI) by LPBM; however, reasons for decreased DMI measured from LPRPL remain unclear. Lower DMI from LPBM did not limit milk production. Supplemental LYS only benefited milk protein content when dietary CP was high; however, low-CP diets, LPBM and LPRPL, had improved feed efficiency compared with HPHL, resulting from similar energycorrected milk (ECM) yields and lower DMI. Results suggest that low CP diets balanced for metabolizable protein (MP) LYS can sustain similar production compared with higher CP diets. Improved performance from LPLL suggests the least amount of MP LYS was sufficient for cows at this stage and amount of production. Study 2 sought to identify production differences among cows fed a common CP-deficient basal diet supplemented with: no additional rumen-protected amino acids (AA) (CON), encapsulated methionine (MET) to supply 10 additional grams of MP MET (EM), sprayfreeze MET to supply 10 additional grams of MP MET (SFM), or spray-freeze MET and rumen-protected histidine (HIS) (SFMH) to supply 10 additional grams of MP MET and HIS. The study design was a randomized complete-block design utilizing 44 dairy cows. Cows adapted to the basal diet for 10 d before undergoing a 28 d rumen-protected AA supplementation and data collection period. Amino acid supplementation resulted in similar milk production among treatments; however, milk fat percent and yield were both significantly greater (P < 0.05) for CON compared with EM and SFM. Increasing MP MET supply from 1.9 to 2.3% of total MP through dosage of rumen-protected MET, whether in encapsulated or spray-freeze form, to a low-CP diet had no beneficial effects on lactation performance. Additionally, added rumen-protected HIS increased MP HIS to 2.9% of total MP, compared with 2.5%, but did not increase lactation performance above EM and SFM. Increased DMI above predicted values led to greater CP intakes than expected and positive MP balances for each treatment. This, coupled with current stage of lactation and performance, may contribute to the lack of response to additional MP MET or HIS. Study 3 evaluated metabolic health and production parameters from thirty-one dairy cows fed postpartum diets formulated to be similar in MP, but had differences in MP fractions (i.e. bacterial vs. rumen-undegradable protein). Diets were formulated for 19.1 kg/d DMI, with the control diet (CON) supplying 2,336 g/d MP (1,081 g/d bacterial, 1,165 g/d RUP, 90 g/d endogenous), and the test diet (HiRUP) delivered 2,286 g/d MP (978 g/d bacterial, 1,217 g/d RUP, 90 g/d endogenous). The HiRUP diet included commonly used rumen-undegradable protein (RUP) feed sources in attempts to alter the amounts of bacterial vs. RUP MP fractions. Dry matter intake was similar between treatments, although, a tendency for a treatment by wk effect was apparent as a result of decreasing DMI after wk four postpartum for cows fed HiRUP. Milk production was similar between CON and HiRUP (38.6 vs. 39.1 kg/d, respectively); however, rumen ammonia-N, plasma urea-N and milk urea-N all tended (P < 0.10) to be lower for HiRUP compared with CON. Additionally, milk protein percent tended to be higher for cows fed CON compared with HiRUP (3.00 vs. 2.87%, respectively). Trends from HiRUP, such as depressed milk protein percent and premature declines in milk production suggest cows may need greater amounts of rumen-degradable protein (RDP) early in lactation to support maximal production. Results from these three studies reveal that selection of protein ingredients and additions of production-limiting AA has potential to greatly influence N metabolism and utilization for milking performance. Potential benefits of implementing production-limiting AA or refining ingredient selection to balance for dietary AA concentrations are related to reduced dietary N amounts and diet cost, lessened manure N outputs, but sustained milk production parameters. Nutritionists and producers should be aware of such feeding strategies as N emission and nutrient land application regulations become more stringent.

Library of Congress Subject Headings

Dairy cattle -- Feeding and feeds Amino acids in animal nutrition Proteins in animal nutrition Nitrogen


Includes bibliographical references (pages 119-130)



Number of Pages



South Dakota State University



Rights Statement

In Copyright