Exam 1 Review
• What 5 factors affect the rate witch which populations can be changed by selection.
b. Selection differential
c. Generation interval
d. Genetic correlation
e. Number of traits for which 1 selects
• Heritability (expressed as h^2) is the proportion of the differences that we observe
between animals that can be transmitted to their progeny.
• Rank the following in terms of increasing heritability: growth, carcass, and fertility
a. Low heritability—fertility, growth, and carcass—High heritability
• What’s the heritability equation? Genetic variance / total variance
• What’s the genetic change equation? Heritability X Selection differential
• Genetic interval is the average age of the parents when the progeny is born.
• What’s the average generation interval in beef cattle? 5-6 years
• What’s the selection interval equation? Individual – group average
• What’s an EPD? ½ breeding value
• Change occurs at a rate of what? 1 / square root of traits being selected
• ____ is selection for one trait at a time.
• What does independent culling level establish? Min and max values that are acceptable
for each trait
• Selection index is a means of including several traits and different economic weighting
factors for each trait. Example: $W
• CAB is the largest branded beef product in the USA.
• Cattle must have at least 50% black hide to qualify for CAB.
• An animal’s color can affect the price it brings.
a. Black cattle are more valuable
• Epistasis is where genes at one locus affect the expression of genes at another loci.
• What is a dilution gene? Incomplete gene; example: roan, grulla
• What’s a contemporary group? A group of animals reared together that have the same
sex, herd, and year.
• Be able to explain calving ease direct: It predicts the differences in the % of unassisted
births of a bull when is bred to first calf heifers.
• What is large scrotal circumference related to? Lowered age at puberty in daughters
• What’s stayability? Longevity
• What measurement do we like to see pelvic area in yearling heifers? 144cm
• What’s dystocia? Difficulty calving
a. Primary cause of dystocia? Disproportionately large calf size or birth weight
compared to pelvic area • We breed heifers at 15-16 months of age. What % of their mature body weight should
they weight at breeding? 65%
• Calculate daily weight gain: (Target weight-actual weight) / days till breeding
• What’s an Animal Unit Month (AUM)? The amount of grass it takes to support one
cow/calf pair for 30 days
• Ranches out west need more or less land per cow? More
• What are the 3 categories of slaughter cows? Breaking, boning, and lean
• Georgia has approximately how many beef cattle? Average farm size? 1 million; less
than 50 head
• Frame sizes:
a. Large 1250+ lbs