Cow Herd Efficiency Committee Discusses Adaptability
Definition of environment should be broadened to include economics.
BILLINGS, MONTANA (July 8, 2005) Building on a theme initiated during earlier sessions at the 2005 Beef Improvement Federation (BIF) annual meeting, the Cow Herd Efficiency Committee roundtable was dominated by discussion of cattle adaptability and the potential to enhance it through genetic selection. Cornell Universitys John Pollak noted that adaptability has been defined as the ability to survive within a defined physical environment. Pollak suggested, however, there must be consideration for the economic environment.
We talk a lot about how adaptable our cattle are, but I know of ranches that have had (a succession of) four different biological types in the same environment, Pollak said. Each was replaced by a program perceived to generate more profit. It shows that we have to broaden the definition of environment to include economics.
Pollak cited Nebraskas Rex Ranch as an example of an operation that stresses adaptability of its females to strengthen that trait in bulls it produces. Females in the seedstock herd are scrutinized for production traits such as calf weaning weight, but also for whether they calve unassisted, have acceptable body weight and disposition, and whether they ever require handling separately from the rest of the herd. Females receive an ear notch whenever they fail to meet any one of the established criteria. Sons of females with just one notch are never kept as bulls. Females with two notches are removed from the seedstock herd.
That process combines considerations for physical and economic adaptability, Pollak said.
Dorian Garrick, of Colorado State University, cited high-altitude disease (or brisket disease) as an example of genetic variation for adaptability. The condition affects some cattle living at or above 5,000 feet (ft.) of elevation. Complications result from restriction of blood flow to the lungs due to the reduction of blood oxygen levels. An affected animals heart pumps harder, trying to increase blood flow. Elevated blood pressure results in leakage of fluids into the chest cavity and brisket, and can cause damage to internal organs and heart failure.
Cattle born and raised at high elevations are less susceptible, suggesting adaptability to this environmental challenge. Animals bred at low altitude with no history of natural or artificial selection for performance at high altitude sometimes suffer losses up to 50%. Pulmonary arterial pressure (PAP) testing is used to generate PAP scores as an indicator trait to assist selection for resistance to high-altitude disease. PAP scores are heritable and repeatable when measured by a reliable technician.
Garrick said Tybar Angus Ranch, Carbondale, Colo., has PAP-tested virtually all of its sires since 1984. Based on progeny testing, PAP EPDs have been created for selection of Tybar sires and production of sale bulls that fit the high-altitude environment.
To consider what effect selection for adaptability to the high-altitude environment might have on other production traits, growth trait EPDs for birth weight, weaning weight direct, weaning weight maternal (milk), and yearling weight were computed using Tybar data alone. These were compared to corresponding EPDs from the American Angus Association.
Garrick said results show little difference between Tybars independent ranking of high-altitude-adapted sires and the national ranking with regard to birth weight and weaning weight maternal traits. There were greater differences in rankings for weaning weight direct and yearling weight; however, there was no evidence that the re-ranking was associated with their PAP EPDs, suggesting that other environmental factors must have been responsible for ranking changes.
More research is needed, Garrick said, to investigate genotype-environment interactions that might result from selection for adaptability to specific environments.
by Troy Smith, field editor, Angus Productions Inc.
© Copyright 2005 Angus Productions Inc.
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