Title page for ETD etd-11272006-144805


Type of Document Dissertation
Author Vanimisetti, Hima Bindu
URN etd-11272006-144805
Title Genetic evaluation of ewe productivity and its component traits in Katahdin and Polypay sheep
Degree PhD
Department Animal and Poultry Sciences
Advisory Committee
Advisor Name Title
Notter, David R. Committee Chair
Greiner, Scott P. Committee Member
Lewis, Ronald M. Committee Member
Pearson, Ronald E. Committee Member
Keywords
  • Ewe Productivity
  • Fertility
  • Accelerated lambing
  • Sheep
  • Heritability
  • Reproduction
Date of Defense 2006-11-17
Availability unrestricted
Abstract
The objectives of this dissertation were to evaluate genetic influences on ewe

productivity, its growth and reproductive components, and measures indicative of accelerated

lambing performance. Genetic parameters were estimated for total weight of litter weaned per

ewe lambing (TW) and its components, number of lambs born (NB), number of lambs weaned

(NW) and average weight of lambs weaned (AW), measured as traits of the ewe, and lamb

survival (LS) and weaning weight (WW), measured as traits of the lamb, in Katahdin sheep.

Heritabilities of TW, NB, NW, and AW, were 0.12, 0.12, 0.09, and 0.13, respectively.

Heritability of WW was 0.15 to 0.20. Genetic effects on LS were negligible. Genetic correlation

of TW with NB, NW, and AW averaged 0.30, 0.90, and 0.74, respectively, those of NB with NW

and AW averaged 0.72 and 0.01, respectively, and that between NW and AW averaged 0.50.

Direct genetic effects on WW were independent of NB and NW, but correlation between

maternal genetic effects on WW and animal genetic effects on NW averaged 0.35.

Ewe fertility, NB, LS, and WW were modeled using stochastic simulation and used to

derive NW, AW, and TW to test alternative predictors of genetic merit for TW. A random 8% of

WW observations were set to missing values and AW and TW were recalculated to evaluate the

effects of data reporting inconsistencies on efficacy of different prediction strategies. Four

alternative predictors of estimated breeding values (EBV) for TW involved direct univariate

prediction (TW1), an index of EBV for NW and AW (TW2), indirect prediction using data for

NW and AW and genetic correlations among NW, AW and TW (TW3), and indirect prediction

iii

augmenting TW3 with data and genetic correlations involving NB (TW4). To validate efficacy

of predictors, daughter data sets were generated from the original ewes and their realized TW

were regressed on alternative predictors. Regression coefficients from TW1, TW3, and TW4

were close to the expected value of 0.50 whereas those from TW2 were less than 0.50. Model Rsquare

statistics were similar among predictors when there were no missing WW data but

regressions involving TW1 had lowest model R-square when some WW data was missing.

Ewe lamb fertility (ELF), ages at first, second, and third lambings (AGE1 to AGE3), first

and second lambing intervals (INT1 and INT2), and number of lambings by 38 mo of age

(LAMB3) were evaluated for an accelerated lambing Polypay flock. Relationships among these

traits and NB and WW were estimated. Heritability of ELF, AGE1, AGE2, AGE3, INT1, INT2,

and LAMB3 were 0.14, 0.39, 0.28, 0.36, 0.00, 0.09, and 0.27, respectively. Heritability of AGE2

and AGE3 were negligible after accounting for variation in AGE1. Genetic correlations of ELF

with AGE1 and AGE2 were -0.89, -0.91, respectively, and that with LAMB3 was 0.89. Genetic correlations of LAMB3 with AGE1 and AGE2 were -0.49 and -1.00, respectively. Genetic

correlations of ELF and LAMB3 with direct genetic effects on WW were close to -0.70, but

correlations with maternal genetic effects on WW were 0.88 and 0.58, respectively. Prolificacy

was independent of ELF and LAMB3.

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