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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Genetics and Animal Breeding » Research » Publications at this Location » Publication #97143


item OKUT, H.
item Van Vleck, Lloyd
item BROMLEY, C.
item Snowder, Gary

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Interpretive Summary Previously animal breeders have been forced to assume that the same genes influence performance at different ages. Statistical techniques and com- puting power now allow for testing that assumption. Prolificacy measure- ments of ewes of Columbia, Polypay, Rambouillet, and Targhee breeds were divided into measurements taken when ewes were young (Y, 1 yr), middle aged (M, 2-3 yr) and older aged (0, > 3 yr). Correlations between express- ions of genotype at different ages were estimated. If the correlation is greater than .80, the usual conclusion is that expression is similar enough that the assumption of same genes affecting performance is adequate. The traits of lambs alive at birth and all lambs born were essentially the same. For litter size at birth, correlations between expression in young and middle aged ewes averaged .75 and in young and older aged ewes averaged d.65 indicating that distinction between young and older ages may or may no be important. For litter size at weaning, correlations between genetic expressions at different ages were generally large which suggest little advantage to treating expressions at different ages as separate traits. For litter weight weaned, genetic correlations were variable for young with middle ages (.09 to .96); and generally large, for young with older ages and for middle with older ages. For litter weight weaned, there may be some advantage to considering measurements at one year of age as a differ- ent trait from measurements at later ages. Heritabilities and phenotypic variation were not the same for all age classes which suggests a need to consider whether measurements at different ages should be analyzed as the same or different traits.

Technical Abstract: Genetic parameters for prolificacy traits for Columbia (C), Polypay (P), Rambouillet (R), and Targhee (T) breeds of sheep were estimated with single and multiple-trait analyses by REML using animal models. Traits were number of live births (LAB), litter size at birth (LSB), litter obser- vations ranged from 5,140 to 8,973. Data were divided into ages of ewe: young ages (Y, age of 1 yr), middle ages (M, ages of 2 and 3 yr), and olde ages (0, ages greater than 3 yr). After single-trait analyses, new data sets were created for three-trait analyses for each characteristic with traits defined by age class of ewe. Heritability estimates from single- trait analyses were low; from .01 to .17 for LAB and LSB and from .00 to .10 for LSW. Estimates of heritability for LWW were low to moderate (.00 to .25) and were substantially less for older ewes. Estimates of herit- ability from three-trait analyses were similar to estimates from single- trait analyses. Heritabilities for LAB and LSB were similar and ranged from .01 to .16. Estimates for LSW from three-trait analyses ranged from .03 to .12. For LWW, heritabilities ranged from .00 .25. Direct genetic correlations for LAB, LSB and LSW among age defined traits were similar in direction but different in magnitude. Estimates of genetic correlations indicate that more progress could be made in selection programs for prolificacy traits in some sheep breeds by considering age of ewe as a part of the trait rather than by simply adjusting for ages of ewe. The esti- mates varied considerably across breeds.