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Genetic Selection and Crossbreeding to Enhance Reproduction and Survival of Dairy Cattle
A. J. McAllister
Department of Animal and Food Sciences
Over the past century, dairy cows have been largely bred and selected for milk production traits (milk yield, fat and protein content) and conformation which has resulted in tremendous genetic improvement in milk yield. However, emphases on selection and management for higher yields have negatively affected reproductive and survival traits of different breeds in general and the Holstein breed in particular.
The current project will focus on selection/crossbreeding as genetic avenues to improve dairy cattle performance but with emphasis on field data on reproduction, morbidity, mortality, somatic cell score, and body condition score to develop new selection/management tools and criteria to enhance reproduction and survival in dairy herds. Dairy producers are turning to crossbreeding as a solution to health and fertility problems with purebreds and in response to increased market emphasis on milk components. The economic justification for crossbreeding has not been well established under modern management systems or with several breeds of cows that have experienced dramatic genetic change since crossbreeding trials of 30-40 years ago.
Crossbreeding trials, currently underway will provide the data to test the lifetime economic value of crossbred dairy cows against purebreds, primarily Holstein,under both research herd and commercial conditions and will allow determination of the optimum combination of additive genetic merit and non-additive genetic merit in improving lifetime economic performance. Of particular interest will be performance and economics of crossbred animals in regard to fitness and health traits. Resulting indexes will enable producers and industry personnel to make intelligent use of numerous genetic evaluations on an expanding array of traits and large numbers of bulls and cows available for selection.
A major objective of continued regional research collaboration of the proposed project is to give more detailed definition of lifetime economic performance of dairy cattle and ways to use the indexes to bring about change in the traits encompassed by it. The adoption of crossbreeding at an increasing rate apparently seeks to improve these health and fitness traits. At present, selection indices provided to US dairy farms are based on relative net income over opportunity costs (RNIOC), which reflect net lifetime income per animal. Indices based on economic efficiency, which reflects net return per dollar invested, may be more appropriate for genetic improvement programs that involve a combination of purebred selection and crossbreeding.
The tools developed within this project will allow objective, profit-based comparisons of alternative purebred selection (with attention to avoidance of inbreeding) and crossbreeding programs or combinations thereof. As a result of the proposed project, farmers, extension agents, and breeding advisors will be able to make informed decisions regarding the expected short and long-term performance, risk and net profit of their genetic programs from the protocols recommended.
2010 Project Description
This project is part of a three state collaborative effort of the University of Kentucky, Virginia Tech University and North Carolina State University. Genetic groups for the project in the University of Kentucky herd are purebred Holstein (HH, n=33), purebred Jersey (JJ, n=22), and reciprocal Holstein sire X Jersey dam (HJ, n=19) and Jersey sire X Holstein dam (JH, n=19) reciprocal crossbreds which were produced to examine the merit of crossbreeding on reproduction and survival. Collection of heifer growth, reproduction, health and survival data of these females born alive have continued.
First calving of project females is complete, concluding the collection of birth information, calving difficulty, and calf and heifer growth, reproduction and health data of these groups. Collection of lactation, reproduction and health data is continuing for the four genetic groups. To date the females of the original genetic groups have produced 27 Holstein replacement heifers, 14 Jersey replacement heifers and 44 three-way cross heifers sired by either Brown Swiss or Scandinavian Red sires which were bred to the reciprocal crossbreds. Collection of birth information, calving difficulty, and calf and heifer growth, lactation, reproduction and health data of the offspring of the original genetic groups is continuing.
Survival rates of females at the University herd from a live birth to calve for a first time for the genetic groups were: HH (24/33=73.0), HJ (17/19= 89.5%), JH (18/19=94.7%) and JJ (20/22=91.0 %). Further, from the contemporary genetic groups born at Kentucky from 2004-2007 heifer replacements produced thus far have been HH=25, HJ=19, JH=21 and JJ=12. The four original genetic groups have calved one or more times and initiated the following number of lactations per female born alive in each of these groups as follows: HH (n=33) , 1.58; HJ (n=19), 2.32; JH (n=19), 2.37; JJ (n=22), 2.27. The distribution of lactations initiated is similar for all genetic groups except the HH group.
The Kentucky data indicate reduced longevity of the HH group relative to the two reciprocal crossbred groups and the purebred Jerseys. Similarly, the HH group produced proportionately fewer female progeny per original female born alive in this genetic group compared to the HJ, JH and JJ genetic groups and provided evidence of possible lower female net replacement rate. Lifetime milk production to date per female calving at least once and per female born alive show an advantage for the HJ and JH groups compared to the HH and JJ groups.
Results from the Kentucky station indicate a lower survival and net reproductive rate of the purebred Holsteins compared to the reciprocal F1 Holstein x Jersey and Jersey x Holstein crossbreds and the purebred Jerseys. These kinds of calculations will be the ones necessary to evaluate the value of crossbreeding for lifetime performance of dairy cattle. Preliminary results have been shared at dairy farmer meetings.