Factors contributing to differences in stress resilience and growth performance between <i>Bos taurus</i> and <i>Bos indicus</i> cattle

Abstract

• Understanding genetic differences between Bos taurus and Bos indicus cattle that have allowed each subspecies to become better adapted to their environments can enable targeted breeding strategies to enhance genetic potential, while improving animal growth and production sustainability. • Bos indicus cattle have superior thermoregulatory and heat tolerance capacities compared to Bos taurus cattle due to physiological and metabolic adaptations. • Bos indicus cattle have reduced maintenance energy needs, decreased voluntary intakes, and are better able to handle nutritional and hydrational stress, but research reports are conflicting when considering feed efficiency and animal growth. • Bos indicus cattle have a stronger antipredatory response and exhibit heightened stress-related physiological responses that make them more reactive to restraint, weaning, transport, and other human handling practices, which have substantial effects on animal welfare and growth. As the world population is projected to increase to 9.15 billion by 2050, demand for agricultural products is expected to increase 60% (Alexandratos and Bruinsma, 2012). Current cattle production practices will not meet increasing demand. The U.S. primarily produces Bos taurus cattle and ranks first in beef exports worldwide, accounting for 20% of the world supply (Colditz and Hine, 2016; Scheffler, 2022; USDA, 2024). Brazil primarily produces Bos indicus cattle and is the number two beef producer, supplying 18% of the world’s beef. (USDA, 2025). Exports from Brazil are expected to reach 23% by 2028, providing nearly 2.9 million metric tons of beef annually (Erik O’Donoghue, 2019; USDA, 2019, 2025). This increase in beef production by Brazil is anticipated due to increasing animal numbers, and selecting cattle that have improved performance in tropical climates, such as Bos indicus cattle (Thrift and Thrift, 2003; Scheffler, 2022; USDA, 2024). Worldwide, the cattle industry utilizes both Bos taurus and Bos indicus cattle to meet consumer demands; global beef production by country is shown in Figure 1. These two subspecies of cattle are distinctly different physiologically and genetically, impacting the beef that is produced. Bos taurus cattle, commonly found in temperate regions, tend to have superior carcass characteristics and meat quality and rapid growth rates, but are less adept at managing environmental stressors such as heat and nutritional stress (Colditz and Hine, 2016; Scheffler, 2022). Bos indicus cattle, which are native to tropical and subtropical climates, demonstrate superior resilience to greater temperatures and nutritional burden. (Thrift and Thrift, 2003; Eberhardt et al., 2009; Scheffler, 2022). Examples of typical Bos taurus and Bos indicus cattle are depicted in Figure 2 and global distributions can be seen in Figure 3. Although these different subspecies have adapted to distinct environments, it is also worth noting that each subspecies has also demonstrated adaption to unideal environments (O’Neill et al., 2010; Lima et al., 2020). Metabolically, Bos indicus cattle have a lower basal metabolic rate, increased hemoglobin levels and increased longevity compared to Bos taurus cattle (Howes et al., 1963; Chenoweth, 1994; Hansen, 2004). However, Bos taurus cattle have superior carcass traits and meat quality attributes (Crouse et al., 1989; Beatty et al., 2006; Scharf et al., 2010). Global beef production by country in metric tons. Data adapted from USDA Foreign Agricultural Service (USDA, 2025). Global distribution of bovine species. Figured adapted from Zhang et al. (2020). Depictions of typical Bos taurus and Bos indicus cattle. Panel A shows a Bos taurus Angus cow, and Panel B shows a Bos indicus Brahman bull. Photo A (Colyer, 2025), photo B (BRCRanch, 2025). Various traits of these two subspecies have been shaped by a combination of their genetic identity and response to environmental factors. By examining the genetic and subsequent molecular differences between these two subspecies, we can better understand what makes each unique. As climate change continues to impact environmental conditions, the development of resilient cattle has become increasingly critical. Knowledge regarding the unique strengths of each subspecies of cattle can inform producers and aid in the development of more efficient breeding programs that integrate the strengths of each subspecies to produce livestock capable of thriving across diverse environments. Although there are numerous studies that have compared Bos taurus, Bos indicus, and crossbred cattle, this review will primarily focus on differences between the two subspecies. The physiological and phenotypic differences observed between Bos taurus and Bos indicus cattle can be explained by molecular differences. The divergence of these subspecies is estimated to have occured between 117,000 and 275,000 years ago based on mitochondrial DNA (mtDNA) (Bradley et al., 1996), and between 610,000 and 850,000 years ago using microsatellite data (MacHugh et al., 1997). A simplified cattle phylogenetic tree is shown in Figure 4. Since this divergence, the genomes of Bos taurus and Bos indicus cattle have undergone mutations and selection pressure, ultimately enabling cattle to become better adapted to their environments. Continual change within the nature of the world and environmental conditions requires continual adaptation, both across generations and within an animal’s lifetime. Humans have contributed significantly to these adaptations, as humans domesticated and artificially selected for traits deemed desirable within their operations. This selection, both natural and artificial, contributes to observed genotypic and phenotypic differences present between today’s Bos taurus and Bos indicus cattle. Simplified cattle phylogenic tree created by Cooke et al. (2020), based on data from Loftus et al. (1994). Molecular analyses comparing Bos taurus and Bos indicus genomes via examining differences in single-nucleotide polymorphisms (SNPs), quantitative trait loci (QTL), copy number variations (CNV), alleles, indels, and microsatellites have been conducted (MacHugh et al., 1997; Bolormaa et al., 2013; Pérez O’Brien et al., 2014; Hu et al., 2020). These studies utilized a variety of techniques including but not limited to genome-wide association studies (GWAS), genomic prediction and selection (GS), marker-assisted selection (MAS), genomic marker imputation, QTL mapping, parentage testing, and genomic marker-based disease testing. Notably, several studies have utilized GWAS to analyze specific genomic regions that regulate skeletal muscle growth and development (Utsunomiya et al., 2013; Terakado et al., 2018; Mohammadabadi et al., 2021; Bejarano et al., 2023). Collectively, results of these studies identify SNPs and QTLs that affect growth traits, which could allow for inter-breed genetic comparisons and subsequently improve future breeding strategies. Other studies identified variations in regulatory regions that influence gene expression and cellular stress responses (Sajjanar et al., 2024). Epigenetic modifications and DNA methylation patterns in relation to environmental stress conditions have also been studied (Sajjanar et al., 2024). Although numerous genetic and molecular differences have been identified between these two subspecies, a broader understanding of how these differences contribute to variation in growth and other phenotypes is needed. The first Bos taurus genome was published to NCBI in 2009, as part of the Bovine Genome Project and has been extensively studied due to the breed’s prevalence within American agriculture. Contrastingly, the first and only Bos indicus genome was published to NCBI in 2014, and subsequent analysis remains comparatively limited. Current literature regarding Bos indicus genetics largely focuses on the breed's enhanced ability to handle environmental and physiological stressors such as heat, hydration, and parasites. Since their divergence, Bos taurus and Bos indicus cattle have each adapted to different environments that contribute to physiological and phenotypic variation known to alter thermoregulatory and heat tolerance capacities of each subspecies. Thermoregulation significantly impacts both health and growth rates of beef cattle, as heat stress and extreme weather conditions reduce feed intakes and activity levels, diverting energy from growth-related processes (Bunning and Wall, 2022; Thornton et al., 2022; Habeeb et al., 2023). Thermal stress, particularly in hot and humid regions, is a substantial challenge in the beef production industry. It is estimated that over 65% of the world’s cattle reside in tropical and subtropical climates. (Sarlo Davila et al., 2019). In the United States, thermal stress within the beef production industry resulted in $369 million in economic losses due to reduced animal performance and lower pregnancy rates (St-Pierre et al., 2003). These economic losses are projected to increase as climate change continues to alter global environmental conditions (Hahn, 1999; Renaudeau et al., 2012). One potential solution to mitigate these economic losses is the incorporation of Bos indicus genetics into beef herds as they are better adapted to heat stress and demonstrate superior thermoregulatory capabilities compared to Bos taurus cattle (Hansen, 2004). The superior ability of Bos indicus cattle to regulate their body temperature has been attributed to a combination of increased capacity for heat loss and reduced heat production (Scheffler, 2022). Bos indicus cattle possess smooth, slick hair coats that are often lighter in color, which helps reflect sunlight and prevent heat absorption (Thrift and Thrift, 2003). Differences in skin morphologies between Bos taurus and Bos indicus cattle have also been observed (Jian et al., 2014), such that the two subspecies differ in sweat gland shape and sweating rates. Histological depictions of sweat gland morphologies of Bos taurus and Bos indicus cattle are depicted in Figure 5. Numerous studies have demonstrated that when compared to Bos taurus cattle, Bos indicus cattle have more well-developed sweat and sebaceous glands (Thrift and Thrift, 2003) that also have an increased density (Turner and Schleger, 1960; McDowell, 1972) and volume (Pan, 1963), and are closer to the skin’s surface (Nay and Hayman, 1956). These attributes contribute to Bos indicus cattle having increased sweating rates, allowing the animal to lose heat and moisture via evaporation (Dowling, 1955; Allen, 1962; Schleger and Turner, 1965). These physiological adaptations synergistically enhance the ability of Bos indicus cattle to minimize heat absorption and maximize heat dissipation. Histological picture of sweat gland morphology of Bos indicus (Panel A), Bos taurus (Panel D), and Bos taurus and Bos indicus crossbred cattle (Panels B and C) taken by Jian et al. (2014). In terms of heat production, Bos indicus cattle have lower metabolic rates than Bos taurus cattle (Frisch and Vercoe, 1977). Metabolic rates are determined by the amount of heat produced by different organs and tissues, and is dependent on organ size and cellular metabolic activity (Scheffler, 2022). One study found that Bos indicus cattle have smaller metabolically active organs, particularly the heart and liver, relative to body weight than Bos taurus cattle (Hawryluk et al., 2021). On a molecular level, energy is required for nearly all cellular metabolic functions (Scheffler, 2022). Decreasing cellular metabolic rates ultimately impacts basal metabolic rate, and it has been suggested Bos indicus cattle have lower basal metabolic rates and energy requirements than Bos taurus cattle (Frisch and Vercoe, 1977; Elzo et al., 2012; Gomes et al., 2017). As such, the lower metabolic rates of Bos indicus cattle may be the result of smaller metabolically active organs, reduced metabolic processes at the cellular level, or a combination (Scheffler, 2022). The physiological adaptations Bos indicus cattle have made, including changes in skin morphology and decreased metabolic rates, result in increased capacity for heat loss and reduced heat production that improves management of thermal stress. Metabolic adaptations exhibited by Bos indicus cattle allow for better handling of nutritional and hydrational stress compared to Bos taurus cattle. Specifically, lower metabolic rates of Bos indicus cattle contribute to reduced maintenance energy (Frisch and Vercoe, 1977, 1978, 1984; Gomes et al., 2017). It has also been consistently demonstrated that voluntary feed intake is lower in Bos indicus cattle than Bos taurus cattle (Rogerson et al., 1968; Frisch and Vercoe, 1977, 1978, 1984). However, there are no collective conclusions within existing literature regarding the relationship between reduced feed consumption and feed efficiency (Hansen, 2004; Elzo et al., 2009; Coleman et al., 2012). Furthermore, although reduced feed intake is beneficial for minimizing the costs of feed, the reduced intake also limits the amount of energy available for the animal, which has variable effects on animal growth depending on the stage of production. Several studies have shown that Bos indicus calves exhibit improved growth performance prior to and at weaning than Bos taurus calves (Koger et al., 1975; Riley et al., 2007). To elaborate, Koger et al. (1975) conducted a study at the University of Florida Agricultural Research Center in semi-tropical conditions and found that Brahman-sired calves had greater weaning weights than Shorthorn-sired calves. This finding was reiterated by a second Florida study by Riley et al. (2007), who found that Brahman calves had greater weaning weights, average daily gain until weaning, and body condition scores at weaning than Angus calves. However, the average daily gain of Bos indicus cattle in the feedlot has been shown to be decreased compared to Bos taurus cattle (Cooke, 2014; Scheffler, 2022). This shift in growth efficiency from preweaning to the feedlot remains unexplained and elucidates the need for further research to better understand the underlying mechanisms driving these differences. It has been well established within the literature that Bos indicus cattle extract nutrients from low quality feedstuffs more efficiently than Bos taurus cattle (Koger et al., 1975; Frisch and Vercoe, 1977; Turner, 1980; Greene et al., 1989; Elzo et al., 2012). Warm-season perennial C4 grasses are the dominant forages in tropical and subtropical regions, and feeding these forages significantly influences the productivity of beef cattle systems (Cooke et al., 2020). These C4 grasses have reduced nutritive value compared to C3 forages typically found in more temperate climates (Cooke et al., 2020). As such, the ability of Bos indicus cattle to better utilize low-quality forages can be attributed to their evolving in regions where C4 grasses predominate. Figure 6 shows the percentage of grassland that is covered by C4 grasses across the globe. Percent of grassland that is covered by C4 grasses across the globe. Taken from Luo et al. (2024). Furthermore, Bos indicus cattle can sustain their body condition in suboptimal nutritional conditions better than Bos taurus cattle (Gomes et al., 2017). Bos indicus cattle can also maintain feed intake and fat reserves in response to heat stress better than Bos taurus cattle (Beatty et al., 2004). It has also been demonstrated both in vivo (Fontes et al., 2019) and in vitro (Rocha et al., 1998) that Bos indicus-influenced suckled beef cows had greater resilience to nutrient restriction and to establish pregnancy compared to Bos taurus cows exposed to the same conditions. The relationship between water and feed intake and differences between Bos taurus and Bos indicus cattle have also been explored. When compared to Bos taurus cattle, Bos indicus cattle consume significantly less water per unit of dry matter intake, particularly under heat stress conditions (Winchester and Morris, 1956). In tropical environments, one study indicated that Bos indicus cattle require up to 25% less water than Bos taurus breeds (Romanzini et al., 2024). Additionally, another study found Zebu steers had a smaller water-to-hay intake ratio compared to Hereford steers (Phillips, 1960). When water availability was restricted to half, the same study found that while both breeds experienced a reduction in hay intake, the decrease was less pronounced in Zebu steers than Hereford steers (Phillips, 1960). Together, such studies suggest that Bos indicus cattle have a greater capacity to maintain nutrient intake and productivity under conditions where water and nutrient availability are limited. Cattle temperament is characterized as fear-related behavioral responses that an animal exhibits when exposed to human handling practices (Fordyce et al., 1988). As temperament becomes more excitable, the animal's reactions to various human contact and handling procedures become more aggressive and/or fearful (Cooke, 2014). Beef producers often consider temperament an important trait when selecting cattle (Elder et al., 1980) as it impacts animal welfare and personnel security (Grandin, 1994), and is also moderately heritable (Shrode and Hammack, 1971; Fordyce et al., 1988; Burrow and Corbet, 2000). A more excitable temperament negatively impacts production traits, including growth (Voisinet et al., 1997), immune response (Burdick et al., 2011b), carcass quality (Voisinet et al., 1997), and reproduction (Cooke et al., 2009, 2012). Specifically, several studies have demonstrated cattle with excitable temperaments have decreased average daily gain (Petherick et al., 2002), feed conversion efficiency (Petherick et al., 2002), body condition score (Petherick et al., 2002), dressing percentage (Petherick et al., 2002), and reduced feed intake (Fox et al., 2004; Nkrumah et al., 2007). It has been consistently demonstrated that Bos indicus cattle have more excitable temperaments than Bos taurus cattle, and that Bos indicus are more reactive to stressors such as restraint, weaning, transport, and other human handling practices (Hearnshaw and Morris, 1984; Fordyce et al., 1988; Zavy et al., 1992; Burrow and Dillon, 1997; Voisinet et al., 1997; Cooke, 2014; Mota-Rojas et al., 2024). This can be attributed to Bos indicus cattle having stronger anti-predatory responses than Bos taurus cattle (Sih et al., 2004, 2012; Cooke, 2014; Belgrad and Griffen, 2016). As such, Bos indicus cattle are more vigilant around humans (Welp et al., 2004), and it has been suggested they may be more adept at masking injury and disease (Cooke et al., 2020), which are issues related to both welfare and productivity. Furthermore, Bos indicus cattle exhibit heightened stress-related physiological responses compared to Bos taurus cattle (Stahringer et al., 1990; Fell et al., 1999; Curley Jr et al., 2006; Burdick et al., 2011a; Cooke, 2014; Mota-Rojas et al., 2024), are more susceptible to social stress (Cooke, 2014), and take longer to habituate to new environments (Cooke et al., 2020). Cattle with excitable temperaments have greater circulating cortisol concentrations during handling compared to cattle with more docile temperaments (Stahringer et al., 1990; Fell et al., 1999; Curley et al., 2006; Cooke, 2014). Specifically, Bos indicus calves have greater plasma cortisol values in response to a stress stimulation, such as an adrenocorticotropic hormone (ACTH) challenge, than Bos taurus calves (Zavy et al., 1992). Considering the substantial effects on animal welfare, growth, and productivity, cattle temperament should be considered when developing breeding strategies. Global climate change has had and will continue to have a negative impact on cattle production. With the world population expected to exceed 9.15 billion people by 2050 and the demand for beef products needing to increase by roughly 60% during that time, research focused on improving the balance between while the increasing consumer is an of Bos taurus and Bos indicus cattle exhibit distinct genetic and physiological traits that influence their ability to under various including nutritional stress, hydrational stress, and human handling stress. Understanding how these stressors impact growth and from a molecular to phenotypic and within specific environmental will be in breeding strategies that enhance resilience while production. 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