Introduction

Genetic evaluation predicts the genetic merit or breeding value (BV) of an animal considering its genealogical and phenotypic information (milk production and its components, somatic cell count, conformation, among others)¹. The first genetic evaluation of Holstein cattle in Mexico was performed in 1974 by the University of Guelph (Ontario, Canada) at the request of the Asociación Holstein de México (AHM), including only conformation traits. During the following decades, other traits were included, such as milk (MP), fat (FP), and protein production (PP) in kilograms, and the scoring system for identifying highly productive and functional animals in Mexico was modified^1,2,3. Nowadays, the AHM and the Centro Nacional de Investigación Disciplinaria en Fisiología y Mejoramiento Animal (CENID-FyMA), belonging to the Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), are in charge of performing genetic evaluations every four months for milk production and quality, 27 conformation traits, longevity, somatic cells, and selection indices of the Holstein cattle registered before the AHM. The methodology used to predict these BV was the Best Linear Unbiased Prediction (BLUP), which consists of a mixed model that includes simultaneous equations of fixed and random effects to estimate the variance components based on individual performance and representation of all the genetic relationships between individuals⁴. The results obtained from these evaluations identify the best specimens, providing various options to the farmers for the selection process.

As the exchange of genetic material around the world increases, there is a possibility that the same animal has offspring in different countries, and thus, have more than one genetic evaluation. In Mexico, a high percentage of genetic material is imported as frozen semen; thus, when the imported sires have information in Mexico to predict their BV, they already have a genetic evaluation in their country of origin with more information than in Mexico. To incorporate the information generated globally, Schaeffer⁵ proposed a genetic evaluation methodology that integrates the information from Multiple Across Country Evaluation (MACE). To achieve this, regression equations are constructed to predict the BV of the imported sires based on the importing country, adjusting according to the origin of the information^6,7. There are numerous advantages of using the MACE system, among which are: 1) the performance of sires adjusted by the production information of their daughters from various evaluations of the participating countries and 2) the identification of existing specimens in other countries that may be good breeders under the conditions of the importing country^5,7.

This study aimed to evaluate the impact of Holstein sires foreign information on the genetic evaluation of their MP, FP, and PP traits and to predict the genetic improvement rates expected from these evaluations. By incorporating this information, it is expected to improve the precision of the BV, and therefore, the genetic improvement rates of the evaluated traits.

Material and methods

Results and discussion

The BV obtained in the test differ on average 120 kg for MP (from -200 ± 315 kg in MEX-GE to -80.1 ± 411.5 kg for I-GE), 4.6 for FP (from -2.4 ± 8.2 kg in MEX-GE to 2.2 ± 12.5 for I-GE), and 5.8 for PP (-3.6 ± 7.9 kg in MEX-GE to 2.2 ± 12.3 kg for I-GE). On average, the R are higher in the I-GE than in the MEX-GE; they are even two times higher (from 73 to 30 for MP and from 74 to 29 for FP and PP) when considering the information from productive daughters in several of the participating countries.

In both evaluations (MEX-GE and I-GE), was observed a positive trend in the average genetic improvement per birth year; the BV of the I-GE were higher than those of the MEX-GE throughout the study period (Figure 1). It was also observed a decrease in the average R in the last years of study, which coincides with the low number of born sires in recent years (Figure 2). This decrease in R could be explained by the lower number of daughters of young sires evaluated^18,19. A previous study suggests that the decrease in the average of BV could be because initially, the evaluation only includes few offspring; once the best specimens are selected, these are frequently used to increase the average of the genetic trends within the population and the number of daughters per sire²⁰, which can increase the similarities of the calculated BV between the two evaluations. This is corroborated by observing the differences between the groups created based on the number of daughters they provide to the study (Table 1), where, by increasing this number, the average of BV an R in the MEX-GE and the I-GE approximate to each other, and thus, the (P between both evaluations gradually increase. The β and their standard errors, calculated by regression analysis, show a decrease of approximately half for MP and two-thirds for FP and PP of the MEX-GE with the I-GE (from 23 ± 0.6 kg to 42 ± 0.7 kg for MP, from 0.3 ± 0.02 kg to 0.92 ± 0.03 kg for FP, and from 0.48 ± 0.02 kg to 1.1 ± 0.02 kg for PP), but the behavior of both evaluations is similar throughout the years, this may be due to the adjustment in the genetic bases. Another study concludes that the information generated in the international evaluation is a more precise indicator than the results obtained in the daughters evaluated in a single country²¹, which was confirmed in this study, where was observed increased R for the I-GE in the three traits.

Figure 1 Trend of the breeding values (BV) per birth year of sires included in the Mexican (MEX) and international (MACE) evaluations for milk (MP), fat (FP), and protein (PP) production in kilograms 

Figure 2 Trend of reliabilities (R) per birth year of sires included in the Mexican (MEX) and international (MACE) evaluations for milk (MP), fat (FP), and protein (PP) production in kilograms 

During the first reordering analysis of sires, based on their BV (MEX-GE and I-GE), it was observed a reordering in sires, confirmed by the low calculated (S (0.63 for MP, 0.48 for FP, and 0.55 for PP). This correlation decreases its value by increasing the ips, being the 10% group superior for the three traits than the other groups, which results in only 35% of sires in common. Table two shows the results of the other groups.

In the analysis of ∆Is, when using the highest ips (which includes the highest percentile), was observed a more significant increase for the three evaluations (MEX-GE, I-GE, and MACE-GE) in the three traits, which suggests the use of these sires for the following generations (Table 3). However, it would be necessary to consider various factors within the population (rates of consanguinity, preferential treatment, adaptation to production systems, etc.) to optimize the use of these specimens. Additionally, was observed a higher ∆Is when using the MACE-GE results due to the greater availability of animals since it represents an opportunity to increase the ∆Is, increase the genetic variability, and provide a higher amount of selection material to the producers. However, to recommend its use, it is necessary to consider factors such as environment genotype, germplasm availability, and selection for other population interest traits.

The IGC provides a different way to evaluate the similarity between the MEX-GE and the I-GE countries. The average between the MEX-GE and the 29 participating countries was 0.79 ( 0.04 for MP, 0.80 ( 0.04 for FP, and 0.81 ( 0.04 for PP. The IGC with the countries with which Mexico has a more significant germplasm exchange and that were calculated based on more than 200 sires, such as the United States of America, Canada, the Netherlands, Germany-Austria, Great Britain, Italy, and France, reached medium levels (0.80 approximately). While the highest correlations were observed with Israel, Slovenia, Estonia, Latvia, and Lithuania (reaching IGC of 0.85, 0.86, and 0.87 for MP, FP, and PP, respectively), which could be explained by the low number of sires in common (<50 sires) and their high preference, confirmed by the significant number of daughters (>20 daughters). The lowest IGC were observed in countries with production systems different to those in Mexico, such as: New Zealand, Australia, and Ireland with values of 0.69 for MP and 0.7 for FP and PP). The observed differences between the IGC in the different countries could be because of the sire adaptation to a specific country and not to the differences in the models or preferential treatment of sires²¹. Therefore, if this statement is correct, the estimation of the BV of the sires used at a national level will be closer to those obtained in countries with similar production conditions than those in Mexico. The latter could explain the results obtained with countries that contribute significantly to the number of daughters in Mexico, such as the United States of America, Canada, and the Netherlands, but that do not have the highest IGC with Mexico. These countries differ from Mexico in their production conditions, the definition of genetic bases, estimated heritability indices (h²) for each country, and the complexity of the models used to estimate the BV and the effects applied in each model. Therefore, it is advisable to analyze the groups integrated by countries with similar evaluation conditions, thus expanding the expectations of the international market and exchanging information efficiently.

An area of opportunity for the countries that are members of Interbull is the use and exchange of genomic information, which can bring important benefits to the systems of genetic evaluation; for example, perform a more effective and faster prediction of genetic interactions²², reduced commercialization time of the genetic material, referring to characteristics of reproductive and consanguinity importance²³, which reflects in the increased precision of the BV and their R²⁴.

Conclusions and implications

Foreign information has a positive effect on the MEX-GE, as it improves the R of the BV of the sires used in Mexico, mainly those with a limited number of daughters in Mexico; therefore, it is recommended to continue participating in the Interbull program. In this study, during the arrangement of sires and the verification of the genetic superiority per year, it was observed significant differences in the BV between the evaluations, generating an opportunity to improve the Mexican Holstein population. The sires not used in Mexico and with a high genetic potential for the evaluated traits represent an opportunity to improve the population. Therefore, it is important to identify, evaluate, and incorporate these sires in the Mexican Holstein population. The results obtained after incorporating the MEX-GE to the I-GE show the differences between the participating countries (explained by their diverse production systems, environmental factors, etc.). Therefore, it is essential to consider the use of the international validated information in the selection process of Mexican dairy Holstein cattle and their components, as it will contribute to the increase of the genetic, productive, and reproductive progress of the population.