June 16, 2014

The challenges of meeting nutrient requirements for rangeland livestock


Written by: Jacquelyn Prestegaard

Approximately 60 percent of U.S. beef cattle are raised within the Pacific West, the Southern Plains and the Northern Plains (statistic taken from the Journal of Animal Science). This land is typically dry, barren and devoid of quality forage.

When this land is used for extensive grazing systems, it is a challenge for beef producers to ensure cattle are meeting their nutrient requirements.

Nutrient Requirements of Beef Cattle, commonly referred to as the Beef NRC, serves as a nutrient requirement guide for cattle researchers and producers. It provides guidelines and equations to help predict the most effective diet for their livestock at the most reasonable cost. It is flexible for cattle at different weights, stages of production and weather conditions. Dr. Michael Galyean, the Dean of the College of Agricultural Science at Texas Tech University, said that use of the Beef NRC is very important to researchers.

“The guidelines in the Beef NRC are critical for formulating diets,” said Galyean, chairperson of the NRC committee. “We need to make sure cattle are avoiding any outstanding nutrient deficiencies.”

These equations prove to be accurate in confinement situations where nutrient intake is easily measured. However, nutrient intake is difficult to estimate in the vast expanses of rangeland. As a result, the current NRC model is not always practical for extensive grazing systems.

This concern was the subject of the Beef Species Symposium last year at the 2013 ASAS – ADSA Joint Annual Meeting. Beef nutrition experts suggested the NRC model be updated to account for the wide variation of environmental conditions, dietary characteristics and metabolic demands of beef cattle.

“Some of the biggest gaps in the NRC relate to extensive grazing systems.” Galyean said. “However, finding a way to modify the current NRC model for grazing cattle will be very challenging.”

lone-cattle-109061294762047stjHe also said the current NRC works well for producers in terms of being straightforward, but it is not realistic for a producer to know the body weight and feed intake of each individual animal. Still, he said the NRC should feature an array of models.

“Scientists would benefit from the addition of variables like milk production and calf weight,” he said. “Factors like these can help us better understand the biology of grazing cattle.”

Many sheep and goats are also raised on rangelands where they experience extreme weather and land conditions. Dr. Travis Whitney, Associate Professor of Livestock Nutrition at Texas A & M San Angelo, said estimating nutrient intake is also difficult for small ruminant researchers.

“There isn’t as much literature on sheep and goat nutrition as there is with beef cattle,” he said. “So estimating nutrient intake on rangelands is even more difficult for people researching small ruminants.”

Dr. Bret Taylor, Animal Scientist at the USDA, said the Small Ruminant NRC is rarely used to predict nutrient intake for sheep grazing rangeland.

“Most of our use of the NRC is when sheep are on feedlots,” Taylor said. “We monitor nutrient intake most closely during stages like pre-breeding, near lambing, and early lactation.”

He also said the equations in the current edition of the Small Ruminant NRC provide an excellent baseline for nutrient requirements, but that it would be very difficult to predict those over a variety of rangeland environments.

The eighth revised edition of the Beef NRC will highlight research meant to better evaluate nutrient intake of rangeland cattle. For more information about NRC updates, view the Statement of Task issued by the revision committee.

Related articles published in the Journal of Animal Science:

“An assessment of the 1996 Beef NRC: Metabolizable protein supply and demand and effectiveness of model performance prediction of beef females within extensive grazing systems”

“Potential limitations of NRC in predicting energetic requirements of beef females within western U.S. grazing systems”

“Difficulties associated with predicting forage intake by grazing beef cows”

“Beef Species Symposium: Nutrient Requirements of the Beef Female in Extensive Grazing Systems – Considerations for Revising the Beef NRC”