Research Accomplishment Reports 2007

Metabolic Relationships in Supply of Nutrients for Lactating Cows

K.R. McLeod
Department of Animal and Food Sciences

 

Project Description

Project objectives were to quantify properties of feeds that determine the availability of nutrients critical to milk production.

1a) To quantify effects of feed carbohydrates, proteins, and lipids on rumen microbes and subsequent effects on nutrient supply to the animal.;

1b) To improve and standardize methods for evaluating the nutritional quality of feeds. To quantify metabolic interactions among nutrients that alter synthesis of milk.

2a) To quantify relationships in partitioning of nutrients between body tissues and milk synthesis.

2b) To quantify metabolic responses in cows of differing milk production potential. To use these quantitative relationships to challenge and refine computer-based nutrition systems for dairy cattle.

Specific experiments were conducted to: 1) determine the impact of site dietary carbohydrate digestion on tissue adiposity in growing cattle and 2) to quantify the relationship between metabolizable energy intake and net portal flux of energy substrates and amino acids in forage-fed cattle.

In experiment 1, we demonstrated that adiposity, particularly in the alimentary depots, of growing ruminants is differentially regulated by complexity and site of carbohydrate digestion. In vitro substrate utilization results, in combination with gene expression data, support the novel hypothesis that glucose supply regulates lipogenesis via expression of nuclear regulatory proteins.

In experiment 2, data provided quantitative measures of the PDV effects on energy and amino acid availability for productive tissues, and results suggest that the greater net utilization of some amino acids when ME intake is increased could relate to their catabolism for energy production. Observed data were used to challenge the Cornell Net Carbohydrate and Protein System (CNCPS) model and showed that the model overpredicted AA net absorption, and mean bias represented the largest proportion (87-96%) of the deviation between predicted and observed values. Nevertheless, this comparison suggests that CNCPS may be re-parameterized and used to predict amino acid net absorption when factors describing amino acid utilization by the portal-drained viscera are applied to model predictions.

Impact

Integrative approaches, encompassing multiple levels (i.e. cell, tissue, whole-animal), used in these experiments has yielded unique contributions to predictive model improvement and development. Research in the area of carbohydrate digestion in cattle, where changes in whole-body fat deposition associated with small intestinal carbohydrate supply, have been delineated and ascribed to glucose specific effects on lipogenesis and re-esterification.

Additionally, our research that quantitatively describes the relationship between metabolizable enery intake and amino acid metabolism by the portal-drain viscera has provided unique variables that can be used to re-parameterize the Cornell Net Carbohydrate and Protein System; thus extending model prediction, based on feedstuffs, from absorbed amino acids to amino acids available for productive function. Considering that as much as 25-30% of individual amino acids are metabolized by the the portal-drain viscera, models accounting for this fraction can greatly improve productive efficiency of milk and tissue synthesis.

Publications

El-Kadi, S. W., K. R. McLeod, N. A. Elam, S. E. Kitts, C. C. Taylor, D. L. Harmon, and E. S. Vanzant. 2007. Quantitative assessment of nutrient metabolism by the portal-drained viscera in beef steers consuming graded amounts of forage. J. Anim. Sci. (Submitted; February, 2007).

McLeod, K. R., R. L. Baldwin, VI, M. B. Solomon, R. G. Baumann. 2007. Influence of ruminal and postruminal carbohydrate infusion on visceral organ mass and adipose tissue accretion in growing beef steers. J. Anim. Sci. 85:2256-2270.

Baldwin, R. L., K. R. McLeod, J. P. McNamara, T. H. Elsasser, R. G. Baumann. 2007. Influence of abomasal carbohydrates on subcutaneous, omental, and mesenteric adipose lipogenic and lipolytic rates in growing beef steers. J. Anim. Sci. 85:2271-2282.