Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 1997
Publication Date: N/A
Interpretive Summary: A twinning technology has the potential to improve efficiency of beef pro- duction under intensive production systems. Ovulation rate in puberal heifers is an effective indirect selection criterion to increase twinning rate because of the high genetic correlation between ovulation rate and twinning rate (.89). Repeated observations of ovulation rate for a mean of six estrous cycles results in a trait of intermediate heritability (.33). Thus, breeding values of sires can be predicted with relatively high precision when ovulation rate is determined for six estrous cycles on each of eights daughters.
Technical Abstract: A multiple trait (ovulation rate and twinning rate) repeated records animal model was used to predict breeding value for twinning. The heritability (h2) of ovulation rate rated increased from .07 to .35 for a single estrous cycle to the mean of eight estrous cycles. The h2 for a single observation of ovulation rate and twinning rate were .09 and .07, respectively. The genetic correlation (rg) between them was .89. The fraction of variance due to permanent environmental effects on both ovulation and twinning rate was .04. The h2 of weight traits ranged from .41 to .48 when weight traits were analyzed pair-wise with ovulation and twinning rate. The rg between weight traits with ovulation rate ranged from .16 to .30 and with twinning rate ranged from .30 to .51. Based on year of calving (i.e., 1984 through spring 1996), observed phenotypic mean twinning rate increased from 1.04 to 1.33 calves per parturition while adjusted predicted breeding value (PBV) increased from 1.04 to 1.26 calves per parturition. Based on year of birth (i.e., 1981 through 1993), observed phenotypic mean twinning rate increased from 1.07 to 1.29 calves per parturition while adjusted mean PBV increased from 1.07 to 1.32 calves per parturition. Phenotypic mean ovula- tion rates for fall of 1984 through fall 1994 birth groups increased from 1.11 to 1.26 ova per estrous cycle while adjusted mean PBV increased from 1.11 to 1.29 ova per estrous cycle. Because of the high rg (i.e., .89) be- tween ovulation rate and twinning rate, and because of h2 of .33 for ovula- tion rate for the mean of six estrous cycles resulting in high precision of PBV of sires based on ovulation rate of eight daughter progeny, repeated records of ovulation rate in puberal heifers is an effective indirect selection criterion for twinning rate.