Project Number: 1265-31000-096-13
Project Type: Specific Cooperative Agreement

Start Date: Aug 01, 2008
End Date: Dec 31, 2010

Objective:
This study will utilize genotypes from the Illumina Bovine SNP50 chip on the foundation sires used in the Virginia Tech ¿ Univ. of Kentucky ¿ NC State Univ. crossbreeding project. The purpose of this project is to evaluate the use of genome scans of Holstein and Jersey sires used in a designed crossbreeding study for prediction of production and fitness traits in purebred and crossbred progeny. A further objective is to compare health, fitness, and fertility traits on purebred Holsteins, Jerseys, and reciprocal crosses of those two breeds in the same experiment and to estimate heterosis for these and other traits in Holstein-Jersey crosses.

Approach:
Phenotypes will be collected from animals in three crossbreeding projects. Phenotypes available include disease incidence, reproductive and production data and feed intake data. This crossbreeding experiment utilizes a diallele scheme whereby both males and females of both breeds are mated in purebred and crossbred combinations. The design will enable us to examine the accuracy of genomic prediction of transmitting ability in purebred and crossbred progeny managed contemporaneously. The plan allows estimates of heterosis with precision not possible from field data. Phenotypes will be collected under management conditions that are nearly equal across breed groups. Data analysis to determine utility of genomic information for prediction of daughter performance will be based similar to those outlined by VanRaden (Interbull Bull. 37:33¿36. 2007). Breed group comparisons will be based on mixed models with genetic relationships considered. Heterosis will be measured for the various traits in two ways: as a percentage through the ratio of mean crossbred performance to purebred midpoint; and based on the linear regression of phenotype on percent of heterozygous gene combinations in the animal expressing the trait. In this approach, additive and maternal effects of Holstein genes will be contrasted to Jersey genes in the same model to eliminate those genetic effects from heterosis. Prediction of phenotypes by estimates of transmitting ability of sires (and dams) of cows has been widely used to evaluate utility of estimates of genetic merit. This study will use published estimates of genetic merit as well as research estimates of transmitting ability including genome data to predict performance of purebred and crossbred Holstein/Jersey cows. The utility of genome data for prediction of performance of crossbred animals is unknown. The structure of the diallele cross used in this experiment is ideally suited to address this question. These data will provide a unique test of the ability to predict the performance of crossbred animals and produce information for educational programs. A variety of unique phenotypes may become available during the time covered by this agreement. For instance, blood samples are drawn from animals in the Virginia Tech herd (approximately 40 cows of each breed group) once a week for the first 10 weeks of first or second lactation. These blood samples are being used to determine progesterone levels as well as other blood parameters related to health events such as sub-clinical ketosis. Progesterone profiles can be used as an additional measure of reproductive fitness, as interval to first detection of progesterone indicates the rapidity with which cows return to normal reproductive cycles. Detection of ketone bodies in the blood following calving may prove useful to identifying cows more able to recover from the rigors of calving and cow movement to consume adequate nutrients for high production. Breed group differences will help researchers make good recommendations to dairy producers regarding value of purebreds versus crossbreds.