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ACCESSION NO: 0408094 SUBFILE: CRIS 

PROJ NO: 1265-31000-096-02S AGENCY: ARS 1265 

PROJ TYPE: USDA COOPERATIVE AGREEMENT PROJ STATUS: TERMINATED 

START: 15 JUN 2004 TERM: 14 JUN 2009

INVESTIGATOR: NORMAN H D; DECHOW C

PERFORMING INSTITUTION:

PENNSYLVANIA STATE UNIVERSITY

208 MUELLER LABORATORY

UNIVERSITY PARK, PENNSYLVANIA 16802

GENETIC AND ENVIRONMENTAL PARAMETERS FOR YIELD TRAITS ACROSS VARYING HERD

SIZES, PRODUCTION LEVELS AND LACTATION NUMBER

OBJECTIVES: 1) Determine the effectiveness of using within-herd heritability estimates in genetic

analyses; 2) Estimate change in genetic parameters for yield and SCC across various herd sizes and

herd production levels; and 3) Investigate the use of random regression models to estimate maturity

rate and change in production across lactations.

APPROACH: The cooperator will obtain milk, fat and protein yield, somatic cell scores, herd average

and herd size records from AIPL-USDA. Within-herd heritabilities will be estimated for several

randomly selected herds using REML and compared to estimates using less computationally intensive

methods, including daughter dam regression and paternal half-sib intra-class correlations. Breeding

values will be generated assuming specific within herd heritabilities and compared to breeding values

generated assuming a constant heritability across all herds and from random regression models with

heritability varying across herd sizes and average yield. Estimated breeding values for specific herd

sizes and production levels will be calculated to determine if significant re-ranking of bulls occurs

across various herd parameters. Breeding values for maturity rate (or change in production across

lactations) will be generated by estimating a level for each sire and a linear change across lactations.

PROGRESS: 2004/06 TO 2009/06

Progress Report Objectives (from AD-416) 1) Determine the effectiveness of using within-herd

heritability estimates in genetic analyses; 2) Estimate change in genetic parameters for yield and SCC

across various herd sizes and herd production levels; and 3) Investigate the use of random regression

models to estimate maturity rate and change in production across lactations. Approach (from AD-416)

The cooperator will obtain milk, fat and protein yield, somatic cell scores, herd average and herd size

records from AIPL-USDA. Within-herd heritabilities will be estimated for several randomly selected

herds using REML and compared to estimates using less computationally intensive methods,

including daughter dam regression and paternal half-sib intra- class correlations. Breeding values will

be generated assuming specific within herd heritabilities and compared to breeding values generated

assuming a constant heritability across all herds and from random regression models with heritability

varying across herd sizes and average yield. Estimated breeding values for specific herd sizes and

production levels will be calculated to determine if significant re-ranking of bulls occurs across various

herd parameters. Breeding values for maturity rate (or change in production across lactations) will be

generated by estimating a level for each sire and a linear change across lactations. Significant

Activities that Support Special Target Populations The project is related to in-house objectives 2

(characterize phenotypic measures of dairy practices and provide the industry with information for

determining impact of herd management decisions on profitability) and 3 (improve accuracy of
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prediction of economically important traits currently evaluated). Based on previous work that

demonstrated that heritability varies greatly among herds for milk, fat, and protein yields and somatic

cell score (one measure of mastitis resistance), efforts were begun to determine if variation among

herds for heritability of other measures of mastitis resistance based on producer-recorded health

records was sufficient to allow enhancement of genetic evaluations. Herds with high and low

heritability for mastitis resistance were identified using previously developed methods for estimating

herd heritability with daughter-sire predicted transmitting ability regression. With a threshold model,

heritability for mastitis resistance was 1.6% for low-heritability herds compared with 11.9% for highheritability herds, which indicated that the efficiency of developing selection tools for mastitis

resistance would be enhanced by preselecting herds for progeny testing and genotyping. A scientific

short communication is being prepared for submission to the Journal of Dairy Science. Monitoring

activities for the project included an informational meeting on research collaboration and project

development (University Park, PA) as well as discussion at the 2009 meeting of the Federation of

Animal Science Societies (Montreal, Canada), e-mail, and phone calls. This serves as a final report;

accomplishments included determination of the effectiveness of using within-herd heritability estimates

in genetic analyses and estimation of change in genetic parameters for yield and somatic cell count

across various herd sizes and herd production levels.

PUBLICATIONS (not previously reported): 2004/06 TO 2009/06

No publications reported this period.