Drivers of grazing livestock efficiency: how physiology, metabolism, experience and adaptability influence productivity

Authors: MULLINIKS, JUSTIN - University Of Tennessee; COPE, EMILY - University Of Tennessee; MCFARLANE, ZACHARY - University Of Tennessee; HOBBS, JEREMY - University Of Tennessee; Waterman, Richard

Submitted to: Journal of Animal Science Supplement
Publication Type: Review Article
Publication Acceptance Date: 6/10/2016
Publication Date: 11/9/2016
Citation: Mulliniks, J.T., Cope, E.R., Mcfarlane, Z.D., Hobbs, J.D., Waterman, R.C. 2016. Drivers of grazing livestock efficiency: how physiology, metabolism, experience and adaptability influence productivity. Journal of Animal Science Supplement. 94(Suppl6):111-119. doi:10.2527/jas2015-0711.
DOI: https://doi.org/10.2527/jas2015-0711

Interpretive Summary: Since 1911 (Armsby and Fries, 1911), research has tried to identify “efficient” animals. In 1984, Michigan State University and Colorado State University sponsored the “Beef Cow Efficiency Forum” addressing cow efficiency. However, the implementation of standard criteria to identify energy efficient beef cows has still not been recognized for the beef cowherd. The challenge of pinpointing efficiency traits in livestock production is that livestock in the U.S. graze in a wide variety of environmental and management conditions. These differences provide a challenging situation to have a universal cow efficiency equation. For example, efficiency in one environment does not necessarily equate to efficiency in a different environment. However, certain drivers of efficiency can exist across environmental types such as matching cow type to production environment and increasing metabolic flexibility to environmental stress could be a primary focus for increasing efficiency of grazing beef cows. Knowledge gaps concerning beef cow efficiency fundamentally inhibit advances in selecting for “efficiency” in grazing livestock. The need for a better understanding of the mechanisms driving cow efficiency is critical. Therefore, the objective of this review is to explore drivers and mechanisms of energy efficiency that may identify beef cows that are more efficient converters of rangeland and feed resources into energy. Assuming that a beef cowherd requiring the smallest quantity of dietary calories to perform all functions required to wean a high percentage calf crop, that allow for prolonged lifetime production, will provide for the best opportunity for sustainability. Therefore, the definition of an energy efficient 70 beef cow utilized for this review may be best represented as: A reproductively competent, long-lived cow that consistently uses fewer forage resources (fewer calories needed) to produce a highly desirable energetically efficient calf.

Technical Abstract: Beef cow efficiency, a century’s old debate, on what the criteria, certain phenotypic traits, and definition of an “efficient” cow really should be. However, we do know that energy utilization by the cow herd is proportionally large compared to the rest of the sector. This requirement accounts up to 70 to 75% of dietary energy for maintenance with the residual used for pregnancy, lactation, activity and adaptation to the environment. Therefore, leveraging genetic variation in cow energy efficiency by selecting cows that require less energy for maintenance potentially reduces total energy utilization for beef cattle production, which will ultimately improve production efficiency and profitability. For livestock producers, a critical component is optimizing both economic efficiency and biological efficiency. The continued viability of production systems utilizing rangelands requires more rapid adoption of innovative management practices and selection tools that lend to increased profitability through optimization of nutrient utilization and increased reproductive performance. However, the implementation of a gold standard to identify energy efficient beef cows has not yet been fully realized for the beef industry. Rangeland beef cow herds are required to be biologically and reproductively efficient in an array of ever changing environmental conditions. The most efficient cows are those that easily adapt to these environmental changes and have the knowledge of when to conserve or reset their maintenance requirements to match current environmental conditions. In order to achieve this beef cows have to be knowledgeable of the environment they are being raised in (i.e. learned from their dam and other older herd mates), have a fitness level that establishes of a higher level of utilization of dietary nutrients (i.e. metabolic efficiency), and sound proactive producer (i.e. management) foresight that identifies the need for additional resources (i.e. strategic supplementation) when rangeland forage quality and/or quality is limited. The purpose of this proceedings paper is to identify and describe factors that influence range cow efficiency and ultimately contributes to the sustainability (both from a productivity and economic of range cows in extensive enterprises.