The Siboney de Cuba cattle: a review of studies conducted on the breed

Anel Ledesma-Rodríguez, Filippo Cendron¹, Dervel Felipe Díaz-Herrera, Yuset Fonseca-Rodríguez, Odalys Uffo Reinosa and Mauro Penasa¹

Centro Nacional de Sanidad Agropecuaria (CENSA), Laboratorio de Ensayo para el Control de la Calidad de los Alimentos (CENLAC), Apartado 10, CP 32 700, San José de las Lajas, Mayabeque, Cuba
anelledesma9@gmail.com
¹ Department of Agronomy, Food, Natural resources, Animals and Environment, University of Padova, Legnaro, Italy

Abstract

The Siboney de Cuba cattle breed (5/8 Holstein x 3/8 Cuban Zebu) is the result of more than 50 years of work in crossbreeding and genetic improvement aimed at obtaining milk cattle better adapted to tropical climatic conditions. Its genotype combines the productive qualities of Holstein cattle with the resistance and adaptability of Cuban zebu breeds. These characteristics have made Siboney de Cuba the main dairy cattle breed in the country. Its productive and reproductive traits have been characterized over the years; however, there are very few studies related to the quality and composition of milk for this breed, as well as research carried out within the framework of molecular genetics. The objectives of this study were to review the main research that carried out on the Siboney de Cuba breed and to identify the challenges and perspectives that will be faced by the genetic improvement of this breed in the future.

Keywords: genetic improvement, genomic selection, mastitis, milk quality

Introduction

At the beginning of the 1960s, the Cuban cattle population was composed mainly of zebu animals (96%), destined to meat production and the rest by crossbreeds and small groups of dairy breeds, such as Brown Swiss-Zebu and Holstein-Zebu (Pérez 1999). One of Cuba's main economic and social challenges consisted in the transformation this predominantly zebu population into breeds whose production levels could satisfy the population's growing demand for milk consumption (Acosta et al 2013). The strategy implemented was to increase the milk production of the existing cattle and to obtain, through crossbreeding, a new breed better adapted to tropical conditions (Uffo et al 2013).

With the introduction of the artificial insemination and the massive production of F1 Holstein-Zebu animals, two fundamental lines of development were outlined: the Holstein absorption program and the formation of new breeds. The first one aimed at developing a program to identify bulls able to produce progeny with good milk production coupled with the adaptability to tropical conditions. The second line was aimed at obtaining two new genotypes: the Siboney de Cuba (stabilized in the proportion 5/8 Holstein x 3/8 Cuban Zebu) and the Mambí de Cuba (stabilized in the proportion 3/4 Holstein x 1/4 Cuban Zebu) (Uffo et al 2013).

Photo 1. A heifer specimen of the Siboney de Cuba breed.

During the 1980s, the initial genetic policy was modified to establish the National Genetic Improvement Program (PNMG; Prada, 1983) that included the use of Siboney de Cuba on an important part of the national bovine population. Thus, intermediate levels of Bos taurus x Bos indicus crosses were maintained, especially in those places where conditions did not recommend the increase of Holstein genes.

Siboney de Cuba cattle has shown adequate adaptability and productivity under extreme climatic conditions (Hernández and Ponce 2008). In the early 1990s, the Cuban agricultural sector experienced a severe recession due to the loss of relations with the main traditional trading partners greatly that affected the import of essential inputs and raw materials for animal feed. In these conditions, the fact that the Siboney de Cuba had zebu genes contributed to the subsistence of the breed, due to its greater adaptability and resistance (Ribas et al 2004). Several authors have analyzed the productive and reproductive performance of this breed with the objective of identifying animals of high genetic value, and using them as sires in crossbreeding and genetic improvement programs (Acosta et al 2016; García-Díaz et al 2019; Portales et al 2012).

The objectives of this paper were to review the main research that has been carried out on Siboney de Cuba cattle and to identify the challenges and perspectives that will be faced by the genetic improvement of the breed in the future.

Productive traits

Genetic selection of Cuban dairy cattle is mainly based on milk production (Hernández and Ponce de León 2020). The main traits collected to evaluate the productive efficiency of the herd are milk's volume produced at 244 days, at 305 days and at the end of lactation, as well as the duration of lactation.

Ribas et al (2004) published the analysis of the productive characteristics of Siboney de Cuba in two locations in western Cuba, during the period 1980-1999. The authors reported that cumulative milk production at 244 days averaged 1067 kg for cattle farms located in Pinar del Río and 2045 kg for cattle farms located in Havana; furthermore, the total volume of milk produced was 1119 and 2094 kg and lactation lasted 277 and 305 days, respectively. They concluded that there was a very important effect of the year of study due to the influence of the period of scarcity of inputs (1990s). These results were similar to those obtained by Suárez et al (2009) who demonstrated the existence of a genotype-environment interaction in Siboney de Cuba cattle using the maternal father-grandfather model and the BLUP methodology. Suárez et al (2009) divided the study years into two periods: Normal (1980-1990), during which the animals were maintained under normal conditions and adequate supplementation of concentrated feed, and Low (1991-2000), when there was a significant depression in the conditions of management, breeding and feeding of animals. The authors estimated the influence of both periods on the genotype. They concluded that animals with higher milk production at 244 days (2421 kg) in the Normal period tended to decrease their production in the Low period (1619 kg).

During the 1990s, the drastic reduction in imports and the lack of raw materials necessary to produce food with adequate energy intake caused the death of thousands of animals due to malnutrition, disease and poor handling. This situation explained the decrease in the cows' production levels, evidence of the interaction of the environment on the genotype, an aspect to be taken into account for the selection of the best stallions. According to Suárez et al (2009), it is not only necessary to select animals that perform well under certain conditions, but also that their production remains stable in all circumstances.

Évora et al (2008) analyzed the relationship between the time of incorporation and calving and productive efficiency of primiparous Siboney de Cuba cows. The authors worked with 9590 records of primiparous females that calved between 1979-2006 and reported milk yield values of approximately 2 241 kg, while lactation duration ranged over 286 days. Portales et al (2009) obtained similar results. They used 15275 records of cows born during 1976-2003 and located in two livestock companies in the Cuba western. The authors reported values for milk production in the range of 2036 to 2713 kg during the first lactation, while the average duration of lactation ranged over 290 days.

In another investigation on the influence of non-genetic Daltro et al (2020) in the Siboney de Cuba, Fernández and Suárez (2011) reported values of 2540 kg of milk at the end of lactation, with lactation periods of around 309 days. Those authors included in the analysis lactation records from 1979 to 2000 and values were lower than those obtained later by Hernández and Ponce de León (2020) in a study on cows that calved between 1984 and 2016. Indeed, Hernández and Ponce de León (2020) reported an average accumulated milk production of 3 895 kg and an average lactation duration of 272 days. These differences may be due to the sample size used and the influence of the calving year in which the cows expressed their productions, as well as to the selection and genetic improvement process to which the animals have been subjected.

Arce et al (2017) evaluated the productive traits of dual-purpose Zebu x Holstein cattle in the state of Tabasco, Mexico, during the years 1994-2011 . For the genotype 5/8 Holstein x 3/8 Mexican Zebu, the authors obtained a milk yield of approximately 1263 kg with a lactation duration of 260 days, very similar to what was published for the Siboney de Cuba. Canaza-Cayo et al (2018) in Brazil, determined the genetic factors influencing milk production of Girolando cows. They analyzed milk yield at 305 days during the first three parities. For the 5/8 Holstein x 3/8 Gyr crosses, they obtained an average milk yield of 3 933 kg during the first calving. As the number of births increased, so did the production of milk. For the same breed, Daltro et al (2020) reported milk yield at 305 days that ranged from 4388 kg to 4 772 kg. These performances were greater than those observed for the Cuban breed.

The Siboney de Cuba breed combines the resistance of Zebu cattle with the productive performance of Holstein cattle; however, its productive potential does not reach its maximum expression if the feeding and management are not adequate. Authors such as Amimo et al (2007) have argued that low production levels are not only caused by the climatic effect, but also by the effects of poor forage quality, low concentrate consumption, high incidence of parasites and diseases, and poor economics and infrastructure.

Reproductive traits

Cattle breeding needs a rapid incorporation of females into a new reproductive cycle after calving to achieve the fundamental goal of having a calf every year, or at least every 13 months. This is achieved by decreasing the days open and thus the calving interval. The optimum calving interval is 365 days, while the time between calving and pregnancy should not exceed 100 days. The duration depends on factors such as management, breed, age, duration of postpartum anestrus and early detection of estrus, among others INTAGRI (2018). Days open and calving interval influence the number of calvings during the cow's productive life, which ultimately results in a decrease in milk yield and, therefore, in economic losses for the livestock sector.

Several Cuban authors have demonstrated the marked deterioration of the calving interval and days open in Siboney de Cuba breed (Table 1).

Too long days open may be due to late detection of estrus and repeated ineffective artificial insemination services. In Siboney de Cuba, the number of services per conception ranges from 1.83 to 2.44 (Alonso et al 2014; García-Díaz et al 2019; Ribas et al 2004; Torres et al 2016), values that are higher than those referred to as optimal by INTAGRI (2018). The repetition of services can be due mainly, to sanitary problems, diseases that affect the reproductive cycle, delay in the incorporation time and poor development of the animal due to inadequate feeding. In Cuban cattle breeding the incorporation age of heifers ranges between 20 and 50 months (Hernández and Ponce de León 2020; Portales et al 2012), depending on variations in body weight; however, worldwide it is between 18 and 24 months of age in dependence of the breed (Pereira-Ribeiro et al 2017; Sadek et al 2021).

With respect to feeding, nutritional deficits during gestation and lactation can cause the loss of body condition in females; this leads to late onset of estrus, insemination failures and spontaneous abortions because the cow does not have the necessary body reserves to carry out another gestation.

It should be noted that the age at first calving in Siboney de Cuba cattle ranges between 35-45 months of age (Alonso et al 2014; Évora et al 2008; Hernández and Ponce 2020; Portales et al 2009) so that in many occasions, these animals do not have more than two calvings during their entire productive life. A high age at first calving implies economic losses for the dairy industry, because replacement is not guaranteed and, therefore, its productive and reproductive capacity cannot be fully exploited (Leano et al 2017). All the aforementioned authors agreed that, in addition to the year of calving, the unit and the calving season can influence the productive and reproductive behavior of the Siboney de Cuba, with their interactions being the most significant. The technical preparation of the workers in the dairy companies, the state of the milking equipment, the hygiene of the unit, as well as the problems of feeding and parasitic infestation or health in general, are some aspects that can vary the cattle reproductive performance between dairies of the same territory (García-Díaz et al 2018).

With respect to the calving season, its influence is due to the existence of two well-marked periods in Cuba, the rainy season (May-October) and the low rainy season (November-April). With the arrival of the rains, the availability of fodder increases, but so does the presence of diseases. The high temperatures and humidity of the tropical climate are a stress source for cattle. In response to the hostile environment, animals tend to decrease dry matter intake and increase water intake, along with other physiological and behavioral modifications. These changes in requirements, as well as the strategies adopted by cattle to cope with the stress period, cause a reduction in their productive performance (Ariasa et al 2008).

Heritability of productive and reproductive traits

Reproductive traits are characterized by low heritability as opposed to growth traits, which have medium to high heritability. The low heritability is indicative of poor additive genetic variability, with the environmental component being the most important, which in many cases makes genetic improvement difficult (Falconer and Mackay 1996).

Portales et al (2012) estimated the heritability for productive and reproductive traits in the Siboney de Cuba breed. For this purpose, they studied 15275 records of females born between 1976 and 2003. The authors reported heritability of 0.15 for milk production in the first lactation while reproductive traits (age at first calving) had low heritability (0.05). These results were very similar to those obtained by González-Peña et al (2009) who estimated heritability of milk production up to the ninth lactation (0.14) using a multi-trait animal model. On the other hand, Ribas et al (2004) and Hernández and Ponce de León (2020) estimated heritability of 0.17-0.18 and 0.16 for cumulative milk yield at 244 and 305 days, respectively, whereas for calving interval and days open the heritability ranged from 0.02 to 0.08. Those results were lower than the observed in the Girolando breed, where heritability of 0.27, 0.28 and 0.20 were estimated for milk production at 305 days during the first three lactations (Canaza-Cayo et al 2018). On the other hand, the Cuban results were very similar to those observed for Holstein cattle populations in Brazil, where heritability values of 0.18, 0.02 and 0.04 were reported for milk yield at 305 days, calving interval and days open, respectively (Domínguez-Castaño et al 2021).

It is known that achieving genetic progress for reproductive traits through selection is difficult, because most of the variance is due to the influence of the environment, so its improvement must be done by optimizing health conditions, food and zootechnics management. However, some improvements through genetic selection are feasible.

Chemical composition of milk

Milk and its derivatives are considered among the most consumed animal products worldwide due to their chemical composition rich in proteins, minerals, vitamins and oligosaccharides. The global trend in dairy farming is projected to achieve higher yields in milk quality, mainly proteins and non-fat solids, linked to specific mandatory compliance standards related to production conditions and accepted at national and international level (Alonso et al 2018).

Several Cuban authors evaluated the physical-chemical indicators of milk from Siboney de Cuba cows and concluded that these are within the limits established by the Cuban Standard NC 448:2006 "Raw Milk-Quality Specifications" (Table 2), except for fat and lactose values obtained by Peraza et al (2015). These differences may be due to the characteristics of the type of feed used in the study and the stage of lactation that the animal was in. Alais (2003) considers that milk fat is one of the parameters that varies the most.

Under the climatic conditions of Morocco, Boujenane (2021) determined the milk composition of Holstein cows in the years 2012 to 2016. Fat and protein (3.54% and 3.02%, respectively) were slightly lower than those reported by Ponce and Hernández (2002) and Martinez-Alvarez et al (2017), for Siboney de Cuba cattle, while lactose and non-fat solids were higher. For Italian Holstein breed, fat and protein (4.02% and 3.31%, respectively) were similar to those published for Siboney de Cuba, whereas for Italian Jersey cattle, the levels of fat, protein and lactose were much higher (5.18%, 4.08% and 4.77%, respectively) (Franzoi et al 2021; Roveglia et al 2019).

The differences observed are due to factors such as breed, sample size, stage of lactation, herd management and/or the feeding system adopted in each country. In Cuba, the basic nutritional supports for dairy units are the silvopastoral systems (Ponce and Hernández, 2002), which increase their availability and quality during the rainy months. It has been proven that a decrease in the quality and quantity of the feed supplied to the cattle can affect the milk chemical composition by not meeting the nutritional requirements of cows in production (Alonso 2015).

In a study on the characterization of the lactation curve and dairy components of the Siboney de Cuba, Hernández and Ponce (2008) determined the average 305 day fat, protein and lactose percentages of 301 cows. Fat content ranged from 4.00% to 4.55%, with higher levels towards the end of lactation, whereas protein decreased in the first part (from 3.50% to 3.00%) and increased towards the end of lactation (3.50%). Lactose levels were in the range from 4.48% to 4.90%. Results were very similar to those published by Ponce and Hernández (2002). On the other hand, the lactation curve showed a slightly flattened behavior, an aspect that was also described by Fernández et al (2001, 2004, 2005) and Palacios-Espinosa et al (2016) (Figure 1).

Figure 1. Lactation curve of Siboney de Cuba. Slightly flattening behavior can be observed, especially around peak lactation. Taken from Fernández et al (2004)

The absence of a lactation peak seems to be characteristic of the Siboney de Cuba, but it has been described also in Simmental cattle populations, and in Italian river buffaloes (Macciotta et al 2006; Macciotta et al 2005). It has been shown that certain sources of variation such as environmental factors, body condition of animals at calving and management practices can affect production during a 305 day lactation and hence the shape of the curve (Rekik and Gara 2004). However, Macciota et al (2005) suggest that the occurrence of curves without lactation peak may be due to mathematical problems and the absence of records in the first days of lactation.

Few studies have been conducted in Cuba regarding the milk chemical composition. The low number of research related to the subject is mainly due to the fact that there is no constant recording of quality traits in the dairies and to the limited availability of equipment to perform these analyses. It is necessary to implement policies that establish monthly records of milk chemical characteristics, since satisfactory performance of quality and hygiene indicators are of vital importance to guarantee the population's health, extend the raw milk life and obtain better artisanal derived products (Alonso et al 2018).

In addition, to carry out a good genetic improvement program, it is necessary to have complete information on the productive, reproductive, sanitary and nutritional events of the animals in the livestock units. Therefore, keeping updated records of these indicators is essential to develop the correct genetic and genomic evaluation of dairy breeds.

Prevalence of mastitis in Siboney de Cuba cattle

Bovine mastitis is the main health problem that affects the Siboney de Cuba breed, whose prevalence has been studied by several authors, either for its clinical or subclinical manifestation. High prevalence values have been found for subclinical mastitis with percentages ranging from 45.1% to 66% (Alonso et al 2018; Díaz-Herrera et al 2019; Torres et al 2016 and Ponce and Hernández 2002). These values are higher than reported ones for Holstein and Jersey Cuban herds (37.6% and 33.5%, respectively) (Díaz-Herrera et al 2019).

The prevalence in Siboney de Cuba is higher than that reported for the Holstein Friesian breed in the province of Cañar-Biblián, Ecuador where, for 360 females studied, only 33 were positive for subclinical mastitis, representing 9.1% incidence (Cuenca-Condoy et al 2021). Uddin-Bhuiyan et al (2020), in an investigation on the prevalence of subclinical mastitis in dairy cattle in Bangladesh published values of 29.4% for lactating crossbred cows (Zebu-Holstein Friesian or Sahiwal or Sindhi), i.e., much lower than those reported for the Siboney de Cuba cattle.

The elevated prevalence of subclinical mastitis is an indicator of sanitary violations during milking and/or in the zootechnical management of cows in production, and Siboney de Cuba is not an exception. Mastitis is a complex and multifactorial disease that depends on animal, environmental and pathogenic variables, but it is generally associated with inadequate hygiene of equipment and animals and incorrect milking routines. Late detection of subclinical mastitis cases and lack of prophylactic treatment affect milk production, cause a decrease in physicochemical and sanitary parameters and make it unfit for human consumption (Fesseha et al 2021).

For the case of clinical mastitis, prevalence of 0.96%, 0.90% and 1.80% have been observed in herds with mechanized milking (Diaz-Herrera et al 2019; Ruiz et al 2012, 2014). These results are lower than those published by Yera-Pompa and Ramirez (2016) for Holstein-Zebu crossbred cow populations in Spain, where they found clinical mastitis prevalence values of 4.56 %. Under Egyptian conditions and for Holstein Friesian cattle, incidence values of 30.5% have been reported for cows with high milk yield, while for low milk yield cows the incidence was 6.90% (Abd-el-Hamed et al 2020).

Torres et al (2016) studied the use of copper sulfate in hypocupremic cows with mastitis, and analyzed the relationship between the prevalence of mastitis and reproductive disorders with copper deficiency. In addition, they estimated the effect of copper supplementation on the disease severity. For this purpose, the authors used 335 cows, 231 of the Jersey breed and 104 Siboney de Cuba, from six to nine years old. The study period covered the rainy months from May to October 2015. The presence of clinical and subclinical mastitis was determined, as well as copper deficiency in blood. Supplementation of this mineral was carried out by parental route to 240 Siboney de Cuba cows. The authors reported that 36% of the animals had copper deficiency in blood serum, while the percentage of cows with subclinical mastitis was 55.7% for the Siboney de Cuba breed and 74.0% for Jersey, being these animals the ones that presented a higher incidence of reproductive disorders. In addition, they concluded that copper supplementation, four weeks before calving, had a positive effect on reproductive behavior indicators and contributed to reduce the number of clinical mastitis cases; however, it was not possible to reduce the presence of subclinical mastitis.

Similar results were obtained by Figueredo and collaborators (2017) in a later investigation where they determined the effect of copper supplementation in Siboney de Cuba cows on immunoglobulin levels, the risk of mastitis incidence and fertility. For this purpose, they selected 70 cows with copper deficiencies in blood between the first and second lactation, to which they subcutaneously administered a formulation of copper sulfate ethylene dinitrol tetraacetate at eight months of gestation and 30 days after calving. The authors found that copper and immunoglobulin values in the blood serum were significantly increased in cows treated with the copper formulation, with respect to the control group. In addition, they reported that, in animals supplemented with copper, the risk of subclinical mastitis incidence was reduced by 25%, a result that differs from obtained by Torres et al (2016).

In India, Gakhar et al (2010) determined the effect of copper on milk quality and mastitis prevention in dairy cattle. They chose 14 apparently healthy pregnant females and gave one dose of copper glycinate before dry-off and one dose after calving. The authors reported that, for cows subjected to the treatment, the occurrence of postpartum mastitis was lower (50%) with respect to the control group (70%), since copper increases the phagocytic activity of neutrophils. For pregnant Holstein cows under U.S. conditions, Scaletti and Harmon (2012) analyzed the effect of dietary copper on the response to coliform mastitis and demonstrated a significant association between copper deficiencies and mastitis prevalence caused by E. coli pathogens. On the other hand, Yang and Li (2015) addressed the roles of antioxidant vitamins and trace minerals in mastitis in dairy cattle and posited that copper deficiency decreases the action capacity of neutrophils and increases susceptibility to bacterial infection. Adequate supplementation contributes to decrease the severity of clinical symptoms of coliform mastitis. These studies corroborate the results obtained by the Cuban authors.

Information related to the occurrence of mastitis in Siboney de Cuba dairy cattle is not used as a selection criterion in Cuban genetic improvement programs because dairy units do not keep updated records of mastitis presence either per animal or per herd. It should also be taken into account that mastitis resistance is a complex trait that depends on a genetic component (very low), but also on physiological, anatomical and environmental factors and therefore its heritability is low (approximately 10%; Aranguren-Méndez 2011). A powerful tool to reduce the incidence of mastitis is marker-assisted selection because it allows greater differentiation between phenotypes and increases genetic gain compared to conventional selection. Genome-wide association studies allow the identification of genetic markers associated with candidate genes and quantitative trait loci that affect individual mastitis resistance traits (Kurz et al 2018; Wu et al 2015). However, due to the high cost of genotyping and the lack of reagents and equipment, these studies cannot be currently performed in Cuba.

Molecular studies in the Siboney de Cuba

Breeding and genetic improvement programs in Cuba are based on evaluations that consider phenotypic, yield and reproductive records, pedigree and progeny testing. In addition, with the use of BLUP methodology (Henderson 1975), it is possible to estimate the breeding values (EBV) that are subsequently used to select the animals with the greatest genetic merit within the different breeds that make up Cuban cattle breeding (Hernández and Ponce de León 2020). Although they are reliable methodologies that have been used for decades, progeny testing programs are time consuming and costly.

The first studies with the marker assisted selection approach on Cuban breeds were carried out at the beginning of the current century. Uffo et al (2006) determined the genetic structure of the Criollo de Cuba, Cuban Zebu and Siboney de Cuba breeds through the loci of six milk proteins by means of DNA analysis by polymerase chain reaction combined with restriction fragment length polymorphism (PCR-RFLP). For this purpose, they used 50 animals per breed in their study. The authors reported that all milk protein loci were polymorphic and diallelic, except for the CASA2 locus which showed monomorphic behavior. The gene frequencies of the alleles allowed establishing a molecular racial pattern specific to each breed studied, which evidenced the high genetic variability of these genotypes, an important aspect to be taken into account for the design of genetic selection programs.

In a subsequent study, Acosta et al (2012a) described through two new methodologies the genetic polymorphisms in growth hormone receptors (GH) and prolactin (PRL) in Siboney de Cuba cattle. Their results allowed identifying the polymorphisms F276Y of the GHR locus and S18N of the PRLR locus, creating restriction sites in the GHR locus and PCR-RFLP in the PRLR locus. In another way, Acosta et al (2012b) studied polymorphisms in the stearoyl-coenzyme A desaturase (SCDA) and acyl-CoA: diacylglycerol acyltransferase 1 (DGAT1) genes due to the role of both enzymes in lipid metabolism. For this purpose, they used the amplification methodology creating the restriction site and identified three genotypes in both loci, being the SCD^A and DGAT1^A alleles the most frequent in the Siboney de Cuba. These polymorphisms have been significantly associated with milk production, fat content and the composition of the lipid fraction of milk (Mao et al 2012).This suggests that Siboney de Cuba cattle has genetic potential to increase milk production if genetic selection is directed towards these genes and environmental and nutritional conditions are adequate.

Acosta et al (2016) estimated variance components, genetic parameters and the individual effect of six milk proteins, growth hormone and prolactin on milk production at 305 days of lactation in Siboney de Cuba cows. To determine the single nucleotide polymorphisms, they used the mini-sequencing technique. Their results showed that the eight loci under study had polymorphic behavior, with the β-lactoglobulin and prolactin loci having the most marked effect.

In the past decade, through cooperation with European and Latin American institutions, research aimed at the analysis of genetic diversity by microsatellites and other molecular markers of Cuban native breeds and their comparison with other Ibero-American bovine breeds was carried out, which contributed to the better characterization of Cuban genotypes (Martínez et al 2012; Ginja et al 2013). Both authors demonstrated the high genetic diversity of Holstein x Zebu crosses.

Using the microsatellite genotyping approach, Acosta et al (2013) carried out a study to determine the genetic diversity of five indigenous Cuban cattle breeds. The results showed that a significant amount of genetic variation was maintained in the local cattle populations and that all the breeds studied could be considered distinct genetic entities.

All the results obtained could have constituted the starting point and the basis for the design of genetic selection programs assisted by molecular markers, which would contribute to an increase in genetic gain, the improvement of productive traits of economic interest and the conservation of Cuban autochthonous breeds. However, selection programs are still based only on the results of progeny test and on some methods for estimating genetic value, without taking into account the advantages and efficacy of molecular tools.

Within the framework of molecular genetics and especially genomic selection, Cuban livestock still presents numerous challenges for the identification of elite animals through selection. The livestock industry has a well-established conventional genetic evaluation system and has numerous records of phenotypic and pedigree data. For the implementation of future genomic selection programs that allow high precision in the estimation of genomic breeding values, it will be necessary to start collecting other phenotypic data related to milk quality (fat, total solids, protein, lactose) and animal health (disease diagnosis and somatic cell count, among others). Some authors also suggest the need to incorporate other types of data such as birth weight and udder size, among others, that could be associated with genomic data and that will undoubtedly increase the accuracy of the estimates (Gutierrez-Reinoso et al 2021; Schöpke & Swalve 2016). From this derives the need for laboratory capabilities and qualified personnel to obtain data on milk quality and other traits directly or indirectly associated with animal health.

On the other hand, the high cost of genotyping and the lack of equipment to perform it constitute one of the main obstacles in the implementation of genomic selection programs. Initially, the SNP genotyping process and the computation of genomic breeding values have to be carried out outside Cuba. Governmental funding is needed, as well as the interrelation between ministries and scientific institutions that will make it possible to carry out genomic studies of the Siboney de Cuba in the future. As an alternative in the short term, international collaborations and projects can be established for the genomic characterization of a certain number of animals, which, although it will not allow carrying out genome-wide association studies due to the aforementioned limitations, it will contribute to estimate the genetic structure of the current populations of Siboney de Cuba.

Conclusions

Due to the current situation of Cuban cattle raising, it is necessary to work on the development of more complete and exhaustive phenotypic registries, which include other productive and reproductive parameters traits of economic importance, as well as indicators related to milk quality, somatic cell count in milk and resistance to mastitis. Animal feeding is also an aspect to be addressed in Cuba. As is well known, nutritional deficit can cause reproductive disorders in cattle, disorders that result in productive and reproductive deficiency, as well as economic losses. Supplying animals with the feed they need, with the required quality, is another of Cuba's main challenges.

On the other hand, most of the studies aimed at the genetic improvement of the Siboney de Cuba breed have been based on conventional procedures such as progeny tests and the estimation of genetic value to select the animals with greater genetic merit within the herd. Achieving genomic studies in Cuba is another challenge faced by the scientific sector, but their application will positively influence the genetic improvement of bovine breeds, will contribute to reduce the generation interval and inbreeding and will allow selecting the best specimens from early ages, even before they have reached sexual maturity. Genomic selection is, undoubtedly, one of the tools that the Cuban livestock industry needs to exploit to the maximum the phebrnotypic and genotypic qualities of its dairy breeds.

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