Genetic evaluation of an Genetic evaluation of an index of birth weight and index of birth weight and

yearling weightyearling weight

Michael MacNeilMichael MacNeil

USDA Agricultural Research ServiceUSDA Agricultural Research Service

Miles City, MontanaMiles City, Montana

I = yearling weight - 3.2(birth weight)I = yearling weight - 3.2(birth weight)

Proposed by Dickerson et al. (1974) Proposed by Dickerson et al. (1974)

ObjectivesObjectives

Estimate genetic parameters for Estimate genetic parameters for birth, weaning, yearling, and mature birth, weaning, yearling, and mature weights of CGC weights of CGC

Evaluate genetic responses resulting Evaluate genetic responses resulting from selection based on the indexfrom selection based on the index

Selection LinesSelection Lines

Established in 1989Established in 1989• Control line (n = 912)Control line (n = 912)• Index line (n = 950) Index line (n = 950)

Generation intervalsGeneration intervals• Control line 3.90 Control line 3.90 0.08 yr 0.08 yr• Index line 3.16 Index line 3.16 0.04 yr 0.04 yr

3 generations3 generations 212 kg selection differential212 kg selection differential

CGC populationCGC population

Stabilized composite of ½ Red Angus, ¼ Stabilized composite of ½ Red Angus, ¼ Charolais, and ¼ TarentaiseCharolais, and ¼ Tarentaise

PhenotypesPhenotypes

Birth weight (n = 5,083)Birth weight (n = 5,083) 200-d weight (n = 4,902)200-d weight (n = 4,902) 365-d weight & index (n = 4,626)365-d weight & index (n = 4,626) Cow weight (n = 1,433; 4,375 obs)Cow weight (n = 1,433; 4,375 obs)

Derivative-free multiple-trait REMLDerivative-free multiple-trait REML

Calf traitsCalf traits• fixed contemporary groupsfixed contemporary groups• random direct & maternal additive effects random direct & maternal additive effects • uncorrelated random maternal permanent uncorrelated random maternal permanent

environmental effectsenvironmental effects Cow weightCow weight

• fixed contemporary group effects,fixed contemporary group effects,• random direct additive effects, random direct additive effects, • uncorrelated random permanent environmental uncorrelated random permanent environmental

effects effects

Three Sets of AnalysesThree Sets of Analyses

a single-trait analysis of the indexa single-trait analysis of the index

four 2-trait analyses of the index with four 2-trait analyses of the index with birth weight, 200-d weight, 365-d birth weight, 200-d weight, 365-d weight, and cow weightweight, and cow weight

three 2-trait analyses of 365-d three 2-trait analyses of 365-d weight with birth weight, 200-d weight with birth weight, 200-d weight, and cow weight. weight, and cow weight.

Heritability EstimatesHeritability Estimates

TraitTrait Direct effectsDirect effects Maternal effectsMaternal effects

IndexIndex 0.32 0.32 0.04 0.04 0.05 0.05 0.02 0.02

Birth Wt.Birth Wt. 0.49 0.49 0.05 0.05 0.11 0.11 0.03 0.03

200-d Wt.200-d Wt. 0.30 0.30 0.04 0.04 0.19 0.19 0.04 0.04

365-d Wt.365-d Wt. 0.49 0.49 0.05 0.05 0.04 0.04 0.02 0.02

Cow Wt.Cow Wt. 0.70 0.70 0.04 0.04

Genetic Trends for the Index Genetic Trends for the Index

Genetic Trends for Birth WeightGenetic Trends for Birth Weight

Genetic Trends for 365-d WeightGenetic Trends for 365-d Weight

Genetic Trends for 200-d WeightGenetic Trends for 200-d Weight

Genetic Trends for Cow WeightGenetic Trends for Cow Weight

Relationship of Index to Weight TraitsRelationship of Index to Weight Traits& Response Versus to Selection for 365-d wt& Response Versus to Selection for 365-d wt

Genetic Correlation

With With

IndexIndexWith With

365-d wt365-d wtRelative Relative

responseresponse

Birth wtBirth wt 0.11 0.11 0.710.71 13%13%

200-d wt200-d wt 0.700.70 0.850.85 67%67%

365-d wt365-d wt 0.900.90 -- 73%73%

Cow wtCow wt 0.770.77 0.90 0.90 68%68%

ImplicationsImplications Despite a genetic antagonism that Despite a genetic antagonism that

compromises selection response for compromises selection response for reduced birth weight and increased reduced birth weight and increased postnatal growth, favorable genetic postnatal growth, favorable genetic responses can be achieved. responses can be achieved.

Selection for the index favorably affected Selection for the index favorably affected the shape of the growth curve, restricting the shape of the growth curve, restricting response in birth weight and mature weight response in birth weight and mature weight of cows. of cows.

Selection intensity in experiment was Selection intensity in experiment was reduced relative to that which would be reduced relative to that which would be available across a breed using national available across a breed using national cattle evaluation and AI. cattle evaluation and AI.