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Gorjanc G, Hely FS, Amer PR 2012 Partitioning International Genetic Trends by Origin in Holstein bulls. ICAR, Cork, Ireland.
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Partitioning International Genetic Trends by Origin in Holstein bulls
G. Gorjanc1, F.S. Hely
2 & P.R. Amer
2
1
University of Ljubljana, Biotechnical Faculty, Animal Science Department, Groblje 3, 1230,
Domzale, Slovenia 2
AbacusBio Limited, PO Box 5585, Dunedin, New Zealand
Abstract
Dairy cattle breeding is globalized to a large extent, in particular in the Holstein breed.
Assessing the impact of different sources of genetic gain in such a setting is important to
strategically allocate limited resources. Such an assessment can be achieved by partitioning
breeding values by the origin of Mendelian sampling terms. In order to capture the whole
global Holstein breeding population, InterBull pedigree and associated breeding values were
used. Analysis was focused on the total merit indexes (TMI) from four countries: Great
Britain (GBR), Ireland (IRL), New Zealand (NZL), and USA. Partitioning was performed on
the global and local population scale. Global trends in the TMI of each respective country
reflect the changes in merit of all bulls from all countries included in Interbull analyses. In
contrast, local trends are achieved by weighting the global partitions of each bull by the
number of daughters in the local country, and are therefore not dominated by countries which
progeny test large numbers of animals. Analysis of global trends showed the dominating role
of selection performed in USA on all four TMI. The contribution of USA origin had a large
positive effect on the global GBR TMI trend, a modest positive effect on the global NZL TMI
trend, and a large negative effect on the global IRL TMI trend, but with improvement in
recent years. Analysis of local GBR TMI trend showed a large positive contribution of USA
followed by Canada and approximately equal positive contributions from GBR and The
Netherlands. The local IRL TMI trend showed a dominating negative effect of the USA and
fluctuating positive contributions from The Netherlands, NZL, and GBR. The local NZL TMI
trend showed dominating positive effect of NZL and minor positive contribution from USA
followed by The Netherlands. Overall, results showed the dominating positive and negative
effect of USA on the global TMI trends, while local TMI trends can deviate considerably
from global trends due to country specific breeding practices.
Keywords: Holstein, genetic trends, partitioning, origin
Introduction
The history of the Holstein(-Friesian) breed was written by breeders from different countries
(Felius, 2007). Today this breed is a prime example of globalized breeding (e.g. Brotherstone
& Goddard, 2005). Reproductive techniques enable the easy dissemination of germplasm
from one country to another. Many countries are improving local populations of black and
white cattle with the importation of the top global Holstein germplasm.
Assessing the impact of different countries in such a setting is important to strategically
allocate limited breeding resources. Since experimental assessment is logistically and
financially impossible, Gorjanc et al. (2011) proposed to use the method of partitioning
breeding values by the origin of Mendelian sampling terms (García-Cortés et al., 2008) to
quantify the marginal contributions of different countries to the global genetic trend. Their
application in the global Brown-Swiss breeding population showed that selection in a single
country has had a major positive contribution to genetic trend for production traits, but an
almost exclusive contribution to negative genetics trend for fertility.
The aim of this work was to apply the method of Gorjanc et al. (2011) to assess the
contribution of different countries to global (world-wide) genetic trends in Holstein bulls and
to project these contributions to local genetic trends for a contrasting subset of countries.
Materials and Methods
Data on the global Holstein breeding population were obtained from the Interbull database.
For each bull evaluated at Interbull a sire-dam pedigree and associated breeding values from
the multiple across country evaluation (MACE) system (Jakobsen & Dürr, 2012) were
collected. All available pedigrees and breeding values for animals born between years 1960
and 2003 were used. Analysis was focused on four countries: Great Britain (GBR), Ireland
(IRL), New Zealand (NZL), and USA. For each country considered, MACE results (April
2012 routine run) for all evaluated traits on country specific scale were obtained. From these
data, current country specific total merit indices (TMI) were computed: the profitable lifetime
index (PLI) for GBR, the economic breeding index (EBI) for IRL, the breeding worth index
(BW) for NZL, and the net merit index (NM) for USA. In order to enlarge the number of bulls
in the analysis missing breeding values that are components of TMI were set to the average of
bulls from the same country in the same birth year. Only the TMI values were used in the
partitioning analysis. In addition to global (Interbull) data, total numbers of daughters per bull
up until present were obtained from each country. This information was used to project the
global partitioning analysis to local level as described in more detail below.
The total number of bulls with the available TMI on a global scale was equal to
145,611. However, only a subset of these bulls had daughters in the countries under
consideration for this analysis. The total number of bulls ranged from 1,537 with daughters in
IRL to 21,261 with daughters in the USA (Table 1). The use of foreign bulls from different
countries (origins) was quite dispersed for GBR, IRL, and USA, but highly limited for NZL
(Table 1). The latter can be explained by the pastoral nature of dairy production in NZL, and
the long history of NZL based breeding program targeting the NZL production environment.
Nonetheless, some foreign bulls were used as bull sires in all countries (data not shown).
Table 1. Number of bulls with daughters and TMI data in countries of interest by selected
origins.
Focal country
Origin GBR IRL NZL USA
CAN 1,088 87 / 1,638
DEU 166 70 / 67
DNK 79 6 / 14
FRA 318 157 / 113
GBR 2,652 270 / 83
IRL / 180 / 1
ITA 135 31 / 183
NLD 726 457 / 306
NZL 98 46 4,672 37
USA 1,252 224 1 18,700
Total1 6,529 1,537 4,849 21,261
1 Includes also bulls of other origins
Partitioning of breeding values by origin is performed by allocating an animal’s Mendelian
sampling term to the country of origin and accumulating these terms along the whole pedigree
(for details see García-Cortés et al., 2008 and Gorjanc et al., 2011). At the end of this process
the breeding value of each individual animal is partitioned in origin specific partitions
.
Country specific TMI were partitioned according to the Interbull global sire-dam
Holstein pedigree and country of origin of an animal. Before partitioning, breeding values
were adjusted such that the mean breeding values in year 1960 was zero and scaled by the
standard deviation of breeding values. Total breeding value partitions for TMI for each
country of interest were averaged by bull’s birth year to quantify the contributions of all
countries to the global (world-wide) breeding population of the Holstein breed. These trends,
on each of the 4 different TMI scales, show changes in the global breeding population due to
selection performed in different countries (origins). The same method was applied also for the
analysis of proportion of genes by origin, where breeding values for all animals are equal to
one (Gorjanc et al., 2011).
In order to consider the global impacts on the genetic trend in the local TMI for each
of the four countries, bull breeding values and partitions were weighted by the number of
daughters in a country and again averaged by birth year. This effectively removed bulls with
no daughters in the local country and provided total and origin specific genetic trend for TMI
for each local population. In all plots only origins with the largest contributions were
presented to avoid clutter. While analysis included all the available data since 1960, results
are presented only for the period after 1980.
Results and Discussion
Gene proportion analysis of global Holstein breeding population based on the Interbull sire-
dam pedigree of bulls showed the increasing proportion of genes of USA origin from 1965
onwards (Figure 1). The increase was from about 30% to almost 90% and is levelling off in
more recent years. In these more recent years, the remaining non trivial proportions of genes
in the global Holstein breeding population originate from Canada (between 5 and 7%), New
Zealand (~1.5%), The Netherlands (~1%). These results match with the history of upgrading
populations of black and white cattle with the USA Holstein breed in many countries (e.g.,
Felius, 2007).
Overall the global trend for the USA TMI (NM) was positive (Figure 2); +1.75 TMI
standard deviations in the period between 1980 and 2003. Partitioning analysis showed that
USA dominated the global trend until 1990 when its influence began to gradually reduce to
about 60% of the total global genetic trend in the last years. Other origins that had measurable
contribution to the global trend for the USA TMI were Canada, The Netherlands, Germany,
and France. The importance of these origins has been increasing since 1990. The projection of
global trend to a local trend for USA TMI showed an expected increase of North American
(USA and Canada) contribution and decreased contribution of other countries.
Overall, the global trend for the GBR TMI (PLI) was also positive (Figure 3); +1.86
TMI standard deviations in the period between 1980 and 2003. Partitioning analysis showed
very similar results as for the USA TMI. The majority of influence has come from the USA
with Canada and The Netherlands and to a lesser extent Germany contributing most of the
remainder. Projection to the local trend shows the reduced influence of the USA in
comparison to other origins. On average the local trend is higher for bulls used in GBR, than
the average trend for the global population. This implies that the breeding goal in GBR has
been different from the weighted average of the global population breeding goal (dominated
by selection in the USA), and that bulls imported into the GBR have been selected based on
GBR TMI. GBR partition is also rising in importance in the last years.
Figure 1. Proportion of genes by origin in global Holstein breeding population.
Figure 2. Partitioning of the global (left) and local (right) genetic trend by origin for the USA
TMI – NM (in standard deviation units).
Figure 3. Partitioning of global (left) and local (right) genetic trend by origin for GBR TMI -
PLI (in standard deviation units).
In contrast to global USA and GBR TMI trends, the global trend for IRL TMI (EBI) is
strongly negative (Figure 4). In recent years the average trend is -1.5 TMI standard
deviations. This implies that the direction of selection in the global population is not at all
suitable for production systems in IRL. Partitioning analysis showed that the major
contribution to this negative trend is due to genetic changes attributed to USA and to a smaller
extent to Canada. Negative global trend is driven by the changes of non-production traits in
IRL TMI (calving interval, longevity, and somatic cell scores - data not shown). A recent
improvement in these traits in the North American bulls appears to be negating this negative
trend. Projection to local trend showed an overall improvement after 1990 that can be
attributed to the choice of better than average bulls from North America for use in Ireland.
The positive influence on local IRL TMI trend is due to The Netherlands, New Zealand, and
Great Britain. Selection of bulls within Ireland is also starting to make a favourable
contribution to the local genetic trend in Ireland.
Figure 4. Partitioning of global (left) and local (right) genetic trend by origin for IRL TMI –
EBI (in standard deviation units).
Figure 5. Partitioning of global (left) and local (right) genetic trend by origin for NZL TMI –
BW (in standard deviation units).
Overall, the global trend for the NZL TMI (BW) is positive (Figure 5); +1.25 TMI
standard deviations in the period between 1980 and 2000. Partitioning analysis showed a
sizeable contribution of USA followed by The Netherlands, New Zealand, and Canada.
Projection to local population showed that the local trend is on average much higher than the
global trend. In addition the majority of genetic change since 1980 can be attributed to
selection activities performed in New Zealand. A modest contribution from USA and
Netherlands was evident at approximately 2002, although this contribution does not appear to
be an on-going upward contribution. The contribution from Canadian bulls is slightly
negative over the whole analysed period.
Conclusions
The partitioning analysis of the global Holstein breeding population has shown a major
influence of the USA when considered on a global scale, although this overall dominance of
the USA appears to have been declining. For GBR, having global bulls evaluated on the GBR
TMI index scale through a combination of domestic data recording and participation in
Interbull appears to have allowed faster improvement in the local index than could be
achieved by following the global trend in genetic merit. For countries like Ireland and New
Zealand whose pasture based systems require different trait emphasis compared to other
countries, the existence of domestic sire improvement infrastructure in New Zealand has been
of significant benefit, while in Ireland the historic absence of domestic infrastructure has been
a major lost opportunity.
Acknowledgement
Authors would like to acknowledge the contribution of Jette Jakobsen (Interbull) for
preparation of global Holstein data and for representatives of USA, GBR, IRL, and NZL for
permission to access data, undertake the analyses, and make the results publicly available.
List of References
Brotherstone, S. & M. Goddard, 2005. Artificial selection and maintenance of genetic
variance in the global dairy cow population. Phil. Trans. R. Soc. B 360(1459): 1479-1488.
García-Cortés, L.A., J.C. Martínez-Ávila & M. Toro, 2008. Partition of the genetic trend to
validate multiple selection decisions. Animal 2(6): 821-824.
Gorjanc, G., K. Potočnik, L.A. García-Cortés, J. Jakobsen & J. Dürr, 2011. Partitioning of
international genetic trends by origin in Brown Swiss bulls. Interbull Bulletin 2011(44).
Felius, M., 2007. Cattle breeds: an encyclopaedia. Misset, Doetinchem, The Netherlands,
800pp.