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Title: PARAMETER ESTIMATES FOR DIRECT, MATERNAL AND GRANDMATERNAL GENETIC EFFECTS FOR BIRTH WEIGHT AND WEANING WEIGHT IN HEREFORD CATTLE

Author
item DODENHOFF, J. - IOWA STATE UNIVERSITY
item Van Vleck, Lloyd
item KACHMAN, S. - UNIV. OF NEBR., LINCOLN
item KOCH, ROBERT - UNIV. OF NEBR., LINCOLN

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Some traits of beef cattle have long been known to be affected by maternal effects. For these traits, e.g., birth and weaning weights, a random maternal effect is recommended to be included in models for genetic evaluation. Early on rather complex models were found necessary to fully explain these traits. Willham suggested that the maternal effect of a dam may be affected by the maternal effect of the granddam. An example often given for a grandmaternal effect is the so-called 'fatty udder syndrome'. A granddam with superior maternal ability over-feeds her daughter, and thereby development of her daughter's udder tissue is inhibited so that maternal ability of the daughter is below average. One concern is that a negative influence of dams on their daughters' maternal ability may cause negative bias in estimating covariance between direct and maternal effects. Animal models used to analyze maternally influenced traits typically include direct and maternal effects and covariance between them but may be suboptimal. Results of this study of Herefords suggest that grandmaternal effects may be important for weaning weight. Estimates of variance due to grandmaternal effects are moderate. Correlations with direct and maternal genetic effects are large. Maternal heritability is considerably underestimated if grandmaternal effects are not in the model but exist. Research is necessary to show if reranking of genetic evaluations of animals occurs with models that include grandmaternal effects.

Technical Abstract: Birth and weaning weights adjusted for age of dam from four lines of Hereford cattle were analyzed. Three lines were selected for 1) weaning weight (WWL), 2) yearling weight (YWL) and 3) index of yearling weight and muscle score (IXL). The fourth line was unselected control (CTL). Observations ranged from 1699 to 2811. Number of animals in the pedigrees ranged from 2266 to 3192. Model 1 included random direct and maternal genetic, permanent environmental maternal, and residual environmental effects and fixed sex year effects. Model 2 additionally included random grandmaternal genetic and permanent environmental grandmaternal effects. Estimates were obtained by REML using an average information method. For birth weight, Models 1 and 2 gave almost identical estimates with estimates for grandmaternal heritability near zero. For weaning weight, estimates for direct heritability were similar from both models. Estimates for maternal heritability were .18, .20, .13, and .20 for Model 1 and .34, .31, .13, an .34 for Model 2. For IXL, estimates for variances due to grandmaternal genetic and permanent environmental effects were zero. Grandmaternal heritability estimates for WWL, YWL, and CTL were .05, .09, and .12. Estimates of correlations between direct and maternal genetic effects were -.13, -.44, -.11 and -.26. Estimates of correlations between direct and grandmaternal genetic effects were .21, .83, and .55, and between maternal and grandmaternal genetic effects were -.99, -.84, and -.76. These results suggest that grandmaternal effects exist for weaning weight and maternal heritability may be underestimated if grandmaternal effects are not included in the model.