Crossbreeding can improve the profit for most dairy producers, if economically similar breeds are used. However, it is important to stress that crossbreeding cannot replace pure breeding. Pure breeding is a prerequisite for crossbreeding. The heterosis obtained from crossbreeding is an added bonus on top of the genetic gain created by pure breeding. The size of the bonus depends on the number and types of breeds involved in the breeding program. Most studies report at least a 10 percent increase in total economic gain per cow among F1 crosses between “unrelated” breeds.
During the last century, dairy cattle breeding improved markedly. From initially being based on phenotypic selection with very few measurements, dairy cattle breeding now involves high-tech breeding schemes based on extremely large data files. These data files, in combination with optimized breeding schemes based on systematic progeny testing, have increased genetic gain with ever-increasing speed.
The breeding goal, however, has changed from being primarily focused on milk production and conformation just a few years ago, to a much broader breeding goal that includes functional traits such as fertility, health and calving ease in most of the Western dairy countries. The reason for this change is mostly because of the deterioration of functional traits of cows, which results from the antagonistic genetic correlations between functional and production traits. At the same time, rate of inbreeding has increased within most breeds. Because of the increased need for robust cows in dairy herds with increasing herd sizes, crossbreeding seems very appealing to many.
The genetic level for numerous functional traits has been reduced within many dairy breeds. Therefore, animal welfare of cows and economics of dairying have been adversely impacted. Long term, the genetic change for the functional traits is not sustainable in regard to economic loss or to animal welfare because dairy producers are unable to adequately compensate via improved management for the decreased genetic level for the functional traits. Breeding goals and definition of breeding goals are, therefore, very important parts of sustainability for all species of livestock.
If the breeding goals for a breed are not defined based on future economic circumstances, then commercial dairy producers will avoid that breed, and the breed will diminish in importance. Therefore, if the aim of a breed is survival, then an economically sustainable breeding goal is essential.
In addition to an economic component, the definition of a sustainable breeding goal can include an animal welfare component. The reasons for considering animal welfare are not only based on moral grounds, but also on the assumption that consumers, in the future, will pay more attention to animal welfare issues related to dairy production. Selling products from breeds with sustainable breeding goals will eventually become easier. The extra weight that can be placed on top of purely economic values for some traits is called “non-market” economic weights.
Another important issue related to sustainable breeding is inbreeding. The breeding programs of dairy breeds have been successful in improving production. The cost has been high rates of inbreeding. With existing pedigree information in the Danish cattle database, the level of inbreeding in the Danish Holstein was 3.9 percent for calves born in 2003 with pedigree completeness in five generations greater than 90 percent. This level of inbreeding is slightly below corresponding estimates for U.S. Holsteins.
Inbreeding leads to inbreeding depression, to reduced genetic variation and to higher frequencies of recessive lethal diseases. For dairy cattle, inbreeding depression has been reported for production traits in several populations; however, inbreeding depression also occurs for the functional traits. For recessive lethal diseases such as BLAD and CVM of Holsteins, inbreeding increases the negative consequences of these diseases.
Reduced genetic variation from inbreeding will result in a future reduction in genetic gain even with the same breeding scheme. Results from simulation analyses show a reduction in genetic gain of 20 percent over a 25-year period due to reduced genetic variation from increased inbreeding. Therefore, managing the rate of inbreeding clearly is an important part of sustainable breeding.
For sustainable breeding goals, data recording for the traits of interest is required. Within the Nordic countries, data recording for the functional traits (such as veterinary treatments, reproduction, calving ease and calf size) has been done for the past 25 years. To be usable for calculation of PTA, easy access to the data is essential. Therefore, storage of data in a common database is very valuable.
Quality of data is even more important for calculation of PTA. Dairy producers must appreciate the importance of high-quality data. Making dairy producers and veterinarians, who are responsible for data recording aware of the importance of high-quality data has been a long process in Denmark. For many years, the percentage of Danish herds with valid data recorded for health by veterinarians was approximately 70 percent; however, within the past few years, this has increased to more than 90 percent of herds for all breeds.
A high percentage of health data must be recorded to achieve acceptable accuracy for PTA. Two methods exist to obtain adequate amounts of data for the functional traits – either deliberate data recording or contracting a large number of herds to do the data recording. The first method is the most efficient, but cooperative thinking among the dairy producers is required. The second method is more expensive because many dairy producers must be under contract to provide enough data – especially when functional traits are included in the breeding goal.
Data recording for the functional traits is, in itself, not enough. The breeding scheme needs to be optimized in accordance with the breeding goal, which under most circumstances means larger daughter groups than exist today. Another requirement for sustainable breeding schemes is appropriate control of the increase in rate of inbreeding. The rate of inbreeding is greater than 1 percent per generation in many populations, which has increased the need to monitor the actual rate of inbreeding. Also, tools are needed to control future rates of inbreeding, such as optimal genetic contribution selection within populations.
With dynamic tools for maximizing genetic gain while constraining the future rate of inbreeding, the rate of inbreeding can be kept under control by assuring the parents of future breeding animals are not too closely related. Such methods have been tested in large dairy cattle populations.
When genetic gain is the major focus for selection of sires of sons and bull dams, the result should be substantial genetic gain in the next generation; however, an increase in the genetic relationship between the selected young bulls will also likely result. Closer relationships result in more inbreeding in future generations. If a small decrease in genetic gain can be accepted among the selected bulls, then the degree of relationship will be reduced in the next generation. In the short-term, a little genetic gain is lost when genetic relationship in the next generation is considered. As more weight is placed on relationship, more time is needed to obtain the genetic gain lost in the short-term.
Crossbreeding is another way to increase sustainability for dairy cattle breeding. Inbreeding problems are removed by use of crossbreeding strategies within herds. Heterosis has substantial impact in dairy cattle. The scientific literature has many reports on the meaningful influence of heterosis in dairy cattle. For dairy producers who focus on functional traits, crossbreeding is of special interest because heterosis effects tend to be greater for functional traits, which have low heritability compared to production traits.
In addition to heterosis, the degree to which breeds complement one another needs to be considered to evaluate crossbreeding systems. By choosing breeds for crossbreeding with higher genetic levels for traits of importance than the original breed, rapid improvement might result for these traits. For example, when Nordic Red breeds are used for crossbreeding with Holstein cows, the Nordic Red breeds contribute a higher genetic level for the functional traits.
The reason for inclusion of sustainable breeding, including breeding goals and inbreeding, in a paper on crossbreeding is because “healthy” breeding programs within the pure lines are a prerequisite for crossbreeding. If crossbreeding is used in a population at the expense of genetic gain in the pure breeds then, in the long run, crossbreeding will harm the overall economics of milk production. Used properly, heterosis is a bonus on top of the gain from traditional dairy cattle breeding programs.
One of the most important things in regard to efficient breeding schemes is size of the test capacity for young bulls. With large numbers of crossbred cows in the population, the test capacity might be reduced if crossbred offspring cannot be used to calculate PTA of A.I. bulls. Methods which include crossbred cows in the calculation of PTA must be in place if systematic crossbreeding becomes routine.
Systematic crossbreeding could also reduce genetic gain in the pure breeds if the number of purebred cows is reduced, which would lower the selection intensity for bull dams. As long as the proportion of crossbred cows is less than 50 percent, this should not be a problem. Calculations from New Zealand have shown the reduction in genetic gain will be 10 percent for Jerseys and Holsteins in a systematic three-breed crossbreeding program compared to the present gain, if 90 percent of the New Zealand dairy producers turn to crossbreeding. For Ayrshire, the third breed in New Zealand, an extra genetic gain of 10 percent results because of more progeny-tested bulls than in the present situation.
If new technologies such as genomic selection become important contributors to dairy cattle breeding schemes, the importance of progeny testing and bull dam selection within the whole population will decrease. In that case, the negative side-effects of crossbreeding would be eliminated.
The Næsgård experiment
Because of knowledge from other species and other experiments with dairy cattle, a large crossbreeding experiment was conducted in Denmark from 1972 to 1985. To my knowledge, this crossbreeding experiment was the largest carried out under research conditions, and three pure breeds were maintained, as well as crosses between the breeds. The breeds were Holstein, original Danish Red and Ayrshire, and the experiment included more than 3,000 lactations of cows.
Unfortunately, the results are published only in Danish. The main conclusions from the experiment were:
“F1 heterosis for total economic merit (expressed per live born female calf from birth to first calving or culling) was 9.9 percent when estimated by the dominance model. The obtained heterosis by three-breed rotational crossing estimated by the recombination model was 19.4 percent. The total merit for cows was expressed per heifer in a three-year period from first calving. F1 heterosis was 21.2 percent (dominance model), and the obtained heterosis by three breed rotational crossing was 30.4 percent (recombination model).”
“The estimates for total merit were only slightly dependent on the prices used. A major part of the heterosis for total merit was due to good stayability and high survival rate of crossbreds. The high survival rate among crossbred cows could not be explained by favorable heterosis for yield, reproduction and resistance to diseases but was rather due to general superiority in constitution (robustness). It was concluded that crossbreeding of dairy cattle breeds can be expected to produce a considerable amount of economic heterosis and that crossbreeding is particularly beneficial in herds with sub-optimum environmental conditions.”
Based on the results from this experiment, one might have expected large numbers of dairy farmers to start systematic crossbreeding. That was not the case, and some have argued the results from this experiment came 15 years too early, because dairy producers today think more in terms of economics compared to 15 years ago. Approximately 10 to 15 herds that started crossbreeding at that time have continued using systematic crossbreeding.
A case study – long-term experience with systematic crossbreeding
Ann and Anders Grosen who participated in the survey took over their dairy farm in 1991. At that time, the former owner had started crossbreeding with Danish Red sires in the Jersey herd. They have continued crossbreeding and have done so for many years with a three-breed rotational system using Jersey, Danish Red and Holstein. In the meanwhile, they have become organic dairy producers with their 110 cows. Their income per cow is well above average for organic dairy producers, and the reasons are good production of cows combined with excellent health of their cattle. The production level is 1,418 pounds fat plus protein per cow per year, with average SCC of 296,000 and veterinarian costs per cow per year of $44, which is approximately one-half of normal veterinary costs. Furthermore, they have had only five stillborn calves during the past 12 months.
One nuisance is variation of cow size with Jersey included in the three-breed rotational system, which causes some problems in the milking parlor and for stall sizes. Ann and Anders have addressed this by using Jersey bulls with high PTA for body size and Holstein bulls with low PTA for body size.
The actual breeds selected for crossbreeding are critically important for the success of systematic crossbreeding. In Denmark, most dairy producers initiating systematic crossbreeding have Holstein herds of cows; however, a few Danish Red and Jersey herds have also started crossbreeding. A three-breed rotational system for crossbreeding is recommended.
For Holstein herds, the first breed of sire to use in a three-breed rotational system, obviously, is one of the Nordic Red breeds. The Nordic Red breeds are Swedish Red (SRB), Norwegian Red (NRF), Finish Ayrshire (FAY) and Danish Red (RDM). The approximate population sizes of the breeds are 160,000; 270,000; 210,000; and 45,000, respectively. The breeds are related to some extent because of substantial semen exchange. Somewhat different breeding strategies have been implemented for each of the four breeds, which has resulted in slightly different genetic levels for the various traits. These differences will be reduced in the future because of increased cooperation among the breeds.
In Denmark, Swedish Red sires are used most often for crossbreeding on Holstein females. Danish Red sires with little or no Holstein genes are, of course, also used on Holsteins. In the future, the percentage of Holstein genes in the Danish Red breed will be reduced. As a third breed, Jersey is an obvious choice for Danish dairy producers because Denmark progeny tests more than 60 Jersey young sires each year. However, dairy producers need to be aware of the variation of cow size and milk composition that results when Jersey is used in a three-breed rotation; therefore, the Montbéliarde breed is preferred by some Danish dairy producers over the Jersey breed.
In both the U.S. and Europe, dairy herds are increasing in size, and dairy producers spend less time with each cow. Therefore, robust cows will probably become more important in the future. Because of the increased focus on functional traits in dairy cattle breeding, systematic crossbreeding of dairy cattle is expected to increase substantially in the future. The introduction of sexed semen could accelerate this trend because sexed semen facilitates breeding schemes with F1 crossbred cows in production.
Crossbreeding can provide dairy producers increased economic output and improve the welfare of animals at the herd level. Therefore, crossbreeding can be an important part of sustainable breeding. However, it must be stressed that crossbreeding is not “the total solution” for herds with low management levels or with fertility problems. On the other hand, crossbreeding can be an important contributor to the solution, along with other management tools.
Furthermore, crossbreeding is not a substitute for sustainable breeding schemes in the pure breeds, which require broad breeding goals based on quality data recording for the functional traits and proper control of increases in inbreeding. The combination of sustainable breeding within the pure breeds and systematic crossbreeding at the herd level could provide optimal results for commercial milk production. The gain is expressed as more profit for dairy producers and as improved animal welfare for dairy cows. PD
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—Excerpts from 4th Biennial W.E. Petersen Symposium – “Crossbreeding of Dairy Cattle: The Science and the Impact” Proceedings