S1008: Genetic Selection and Crossbreeding to Enhance Reproduction and Survival of Dairy Cattle (S-284)
Statement of Issues and Justification
Genetic progress in production has been strong and sustained for many years, but undesirable correlated responses continue to occur in fertility, health, and fitness traits. Dairy producers question the need for additional progress in productive traits without simultaneous improvement in these other areas.The research outlined in this proposal will evaluate and develop methods to improve fertility, health, and fitness traits through selection and crossbreeding. The proposal includes a delivery method to implement findings - the lifetime economic merit indexes for sire selection published by USDA. If this research is not undertaken, farmers will continue to look for alternatives to improve fitness traits in dairy cattle that will involve unnecessary sacrifices in lifetime economic merit.
The research proposed is technically feasible. The proposal to implement national genetic evaluations for male and female fertility continues a portion of the current S284 project. Selection indexes to improve lifetime economic merit were also developed in the current S284 project, providing another opportunity to build on an existing framework. Crossbreeding proposals have been reviewed and accepted by coworkers at cooperating institutions prior to this proposal. We limit the number of experimental animals at each station to a sustainable number that allows other work to continue.
Pooled effort in the crossbreeding project is essential to evaluate sufficient experimental animals for reliable results. Further, no one station could conduct an equally valuable project because of confounding of breed group and herd effects. Multi-state proposals to advance genetic evaluation of health, fitness, and reproductive traits are necessary because of the magnitude of these problems in animal breeding. Finally, acceptance of revised national selection indexes by the industry is much more likely if endorsed by the leading research institutions in dairy cattle breeding.
We anticipate that national genetic evaluations for fertility traits will help equip the dairy industry to reverse a gradual decline in reproductive performance of high producing dairy animals. We hold the same expectation for health and fitness traits. Published results from carefully controlled crossbreeding trials will help producers make more informed decisions about the possible role of crossbreeding in their operations. Finally, continued development of national sire selection indexes for lifetime economic merit is essential for US dairy breeders to compete globally in the economic production of dairy products. Such efforts are also essential to insuring a plentiful supply of affordable dairy products for the US consumer.
The National Association of Animal Breeders, a trade organization of the US artificial insemination (AI) industry and one of several stakeholders for genetic research, identified the following research priorities in October 2001: High priority: "Fertility: Work toward development of a national genetic evaluation system for male and female fertility traits. Consider an adjustment for days open in the current lactation for milk, fat, and protein evaluations.
Crossbreeding: Work toward an improved system for coding crossbred animals, and consider methods to incorporate records of crossbred progeny into the national genetic evaluation system." Medium priority: "Calving ease: Refine the data editing and genetic evaluation systems for direct (sire of calf) calving ease, and develop a system for evaluation of maternal (sire of cow) calving ease.
The objectives of this proposal include these specific priorities. In addition, the objectives are structured to anticipate priorities of producers (our most important stakeholders) in the future.
Reproductive costs for dairy cattle are increasing (Lindhe and Philipsson, 1999; Lucy, 2001; Royal et al., 2000). Poor reproductive performance often leads to premature culling of dairy cows. Lucy, 2001, showed that calving interval increased from just fewer than 13.5 months in 1980 to more than 14.5 months in 2000 in 143 commercial herds. Number of inseminations per conception increased from 2.0 to more than 3.5 in the same time period. A UK study by Royal et al., 2000 showed that pregnancy rate to first insemination declined from 56% in the late 1970's to 40% in the late 1990's while percentage of cows with abnormal ovarian hormone patterns increased from 32 to 44%. A decline in fertility of 0.45% per year between 1975 and 1997 was reported in the United States (Butler and Smith, 1989; Beam and Butler, 1999). A study in progress (R. H. Miller, Personal communication, 2001), documents a substantial decline in first service conception rate from 53% to 45% from 1983 to 1999, with greatest declines in the most recent years.
Meanwhile, milk production per cow per lactation increased from 17,444 lbs to 25,013 lbs from 1978 to 1998 for the Holstein breed. Mean breeding values for milk of Holstein cows increased by 4,829 lbs during this period (http://aipl.arsusda.gov/main/data.html#gtrend). High producing cows are increasingly difficult to breed and are subject to higher health costs than cows of lower genetic merit for production (Cassell, 2001). Lucy (2001) implicated management systems with larger herd sizes and more cows per worker, administration of recombinant bST, and increased levels of inbreeding as contributing factors to declining reproductive performance.
Production recording and genetic evaluation systems for milk yield and composition have evolved well beyond those for reproductive performance in the US. One national evaluation system for male fertility encompasses about 25% of cows in the dairy records program (Clay and McDaniel, 2001, Weigel and Rekaya, 2000) but unlike Europe (Interbull, 1998), no female fertility evaluations are published in the US. The proposed research will lead to such a system.
Genetic evaluation programs for reproductive performance are available elsewhere (The Netherlands, France, Germany, and Italy (Interbull, 1998)). International demand for semen produced domestically (NAAB, 1999) is important to maintaining current progeny testing programs. Competitiveness of the US industry could be diminished if genetic evaluations for reproductive traits are not developed. More importantly, US dairy producers need to control reproductive costs to remain competitive in an increasingly global dairy market.
New genetic diagnostic techniques can identify individual loci with major effects in certain families. Research with QTL in dairy cattle has not emphasized calving-related traits such as perinatal mortality (PM) and birth weight. Some QTL for dystocia have been reported, but further investigation of their relationship with QTL for other calving-related traits is needed. The promise of this approach is that calving-related traits and fertility, due to their low heritability, are prime targets for refined techniques for selection of sires for the AI industry. This project will search for QTL associated with calving-related traits. Genetic evaluations for fertility and other reproductive traits developed in this project will enhance identification of QTL for these traits, also. Concurrently, techniques will be developed to enhance genetic evaluation of calving related traits by inclusion of maternal effects on calving difficulty.
Crossbreeding also provides an opportunity to increase the reproductive performance, health, and efficiency of cattle by incorporating favorable genes from numerous breeds, by removing inbreeding depression, and by capitalizing on gene interactions that cause heterosis. Pure Holsteins have exceeded all other breeds of dairy cattle for milk yield. Consequently, Holsteins have dominated among the dairy herds during the past quarter century in the US, comprising more than 90% of cows in dairy herds (Young, 1984). Recent shifts toward multiple component pricing have lessened the economic importance of the Holstein breed's advantage in milk yield.
Intensive selection for higher yield has increased relationships among animals within breed and increased the rate of casual inbreeding. Even diligent mate assignment will ultimately fail to prevent inbreeding depression, as only a limited number of potential mates have desirable enough genotypes to be used. Crossbreeding eliminates inbreeding depression and permits the expression of heterosis. Both inbreeding depression (usually negative consequences) and heterosis (typically positive effects) affect calf survival, fertility, and growth and have important consequences on health and survival of mature cows.
Genetic evaluations of US dairy cattle are calculated within each breed. Cows with sires and dams of different breeds are excluded from USDA-DHIA evaluations unless identified as part of a breed association's "grade-up" program, which leads to purebred status in future generations. This system avoids bias in genetic evaluations within breed but provides no genetic evaluations of crossbreds and no unbiased method of comparing animals across breeds. Crossbreds should be included in genetic evaluations because limited research suggests that they may be more profitable than the average of their purebred parents. NAAB identified an improved system of recording multi-breed ancestry of dairy cattle and commensurate genetic evaluations of crossbreds as priority research interests in the immediate future.
Many of the traits that affect profitability in crosses of modern dairy breeds have not been studied in designed experiments. Indeed, all crossbreeding research involving North American breeds and strains is very dated (McAllister, 2001) if it exists at all. Generation intervals in dairy cattle and resources required to conduct breeding trials limit the ability of individual stations to address this issue effectively.
Most dairy producers trust and use genetic evaluations, but some important traits that affect profit are not now used in selection indexes including reproductive, health and fitness traits of heifers and cows. Electronic data recording on farms provides more detailed accounting of individual cow incomes and expenses than was previously possible. Research to determine which traits to record and how to record them uniformly is needed before genetic theory can be put into action, either through selection or crossbreeding. A multi-state approach is needed to gain knowledge and reach consensus on proposed goals and indexes before seeking industry acceptance. For instance, consensus among participating scientists in the validity of Net Merit (a product of S284 research) during its development encouraged industry adoption and use by farmers.
The ultimate objective of this coordinated research is to develop the information required to establish and achieve more profitable breeding objectives for US dairy cattle. Regional research projects in dairy cattle breeding were vital to the genetic improvement documented earlier. Widely dispersed research herds allowed producers to witness the results and contribute many of the questions addressed. We anticipate similar results from a regional approach, particularly to crossbreeding. Knowledge acquired from this research will allow development of breeding objectives better suited for several segments of the industry, such as grazers or heifer growers.
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