Project Number: 5438-31000-075-00
Project Type: Appropriated

Start Date: Jul 31, 2002
End Date: Jul 30, 2007

Objective:
1) Quantify changes in energy expenditures and amino acid utilization of diverse biological types in response to changes in nutrient availability. 2) Quantify relationships between amino acid requirement and energy availability in cows and ewes. 3) Match energy and amino acid supply to animal needs to improve efficiency and reduce environmental impact of beef cattle. 4) Conduct research focused on improving the feed efficiency of cattle.

Approach:
Objective 1 - The hypothesis to be tested is energy expenditures and amino acid utilization differ among diverse biological types and in response to change in nutrient availability. Changes in energy expenditure and utilization will be determined in populations that represent diverse biological types. Nutrient balance changes, in association with changes in nutrient availability, will be evaluated by use of feeding trials in which mature cows of diverse genotypes will be provided alternative amounts of feed to provide for weight loss, weight maintenance, or weight gain. Changes in resting energy requirements of diverse biological types due to aging will be determined through the use of indirect-calorimetry. A combination of weight stasis studies and energy/nitrogen balance studies will be used to quantify biological type differences in maintenance requirements. The influence of previous nutrition on subsequent weight gain and production performance will be quantified through the use of feeding trials and balance studies. Objective 2 - The hypothesis to be tested is amino acid utilization differs with changes in energy availability. The relationship between amino acid requirement and energy availability will be quantified by using studies that determine the flux of amino acids across tissues, rates of amino acid incorporation into protein, and rates of protein turnover. Amino acid metabolism in a given tissue will be determined using a combination of surgically prepared animals and stable isotopes. The relationship between amino acid utilization and energy availability will be determined in the pregnant, lactating, growing animal, and mature animals fluctuating in weight. Objective 3 - The hypothesis to be tested is supply of energy and amino acids relative to animal needs is related to efficiency. A series of studies will be undertaken to match nutrients (energy, amino acids) available to the animal with nutrient needs of the animal. Nutrient availability will be varied by diet manipulation and intragastric infusion of required nutrients. Differences in energy and amino acid retention and excretion of energy and nitrogenous compounds will be quantified by use of balance studies in combination with indirect calorimetry. Net and unidirectional flux of energy substrates and amino acids across visceral and other body tissues will be utilized to describe mechanisms of changes in nutrient excretion. Objective 4 - Develop methods to measure efficiency in growing/finishing steers, replacement heifers and mature cows. Identify and measure molecular and quantitative variation affecting efficiency. Identify QTL associated with important components of production efficiency.