Dietary glutamine enhances immune responses of dairy cows under high ambient temperature

Quorum sensing effect of chiral d-glutamine on the modulation of the intestinal microbiota of mice by Lactiplantibacillus plantarum A3

BACKGROUND

Amino acids (AAs) are the building blocks of proteins, but they also serve as biological compounds in biochemical processes, and d-AA isomers are increasingly being recognized as important signaling molecules. As the main organic substrate used by cells in the intestinal tract, the role of the chiral specificity of glutamine is still largely ignored.

RESULTS

In a previous study, we found that d-glutamine affected the quorum sensing of Lactiplantibacillus plantarum A3, promoted the release of signaling molecule AI-2 and up-regulated the expression of the LuxS gene. The results showed that when d-glutamine and L. plantarum A3 were simultaneously applied to a mouse model, the diversity and abundance of intestinal flora in both male and female mice were increased. Interestingly, the simultaneous effect of d-glutamine and L. plantarum A3 on the bacterial diversity and abundance of male mice was significantly higher than that of female mice. In addition, the combination of d-glutamine and L. plantarum A3 can improve the host microecology by enhancing the population of Firmicutes such as Lactobacillus and Lachnospiraceae, reducing the population of Fusobacterium and Bacteroides and affecting metabolic pathways such as AA metabolism and transporter transport.

CONCLUSION

d-Glutamine, as a signaling molecule, can better stimulate the endogenous d-glutamine synthesis in mice and be utilized by L. plantarum A3. Furthermore, sex differences in the changes of intestinal microflora are also found in this research. This research sheds some light on the adoption of d-AAs combined with lactic acid bacteria in intestinal tract health treatment. © 2024 Society of Chemical Industry.

Metabolism and Nutrition of L-Glutamate and L-Glutamine in Ruminants

Although both L-glutamate (Glu) and L-glutamine (Gln) have long been considered nutritionally nonessential in ruminants, these two amino acids have enormous nutritional and physiological importance. Results of recent studies revealed that extracellular Gln is extensively degraded by ruminal microbes, but extracellular Glu undergoes little catabolism by these cells due to the near absence of its uptake. Ruminal bacteria hydrolyze Gln to Glu plus ammonia and, intracellularly, use both amino acids for protein synthesis. Microbial proteins and dietary Glu enter the small intestine in ruminants. Both Glu and Gln are the major metabolic fuels and building blocks of proteins, as well as substrates for the syntheses of glutathione and amino acids (alanine, ornithine, citrulline, arginine, proline, and aspartate) in the intestinal mucosa. In addition, Gln and aspartate are essential for purine and pyrimidine syntheses, whereas arginine and proline are necessary for the production of nitric oxide (a major vasodilator) and collagen (the most abundant protein in the body), respectively. Under normal feeding conditions, all diet- and rumen-derived Glu and Gln are extensively utilized by the small intestine and do not enter the portal circulation. Thus, de novo synthesis (e.g., from branched-chain amino acids and α-ketoglutarate) plays a crucial role in the homeostasis of Glu and Gln in the whole body but may be insufficient for maximal growth performance, production (e.g., lactation and pregnancy), and optimal health (particularly intestinal health) in ruminants. This applies to all types of feeding systems used around the world (e.g., rearing on a milk replacer before weaning, pasture-based production, and total mixed rations). Dietary supplementation with the appropriate doses of Glu or Gln [e.g., 0.5 or 1 g/kg body weight (BW)/day, respectively] can safely improve the digestive, endocrine, and reproduction functions of ruminants to enhance their productivity. Both Glu and Gln are truly functional amino acids in the nutrition of ruminants and hold great promise for improving their health and productivity.

Effects of Glutamine on Rumen Digestive Enzymes and the Barrier Function of the Ruminal Epithelium in Hu Lambs Fed a High-Concentrate Finishing Diet

The present experiment aimed to research the effects of glutamine (Gln) on the digestive and barrier function of the ruminal epithelium in Hu lambs fed a high-concentrate finishing diet containing some soybean meal and cottonseed meal. Thirty healthy 3-month-old male Hu lambs were randomly divided into three treatments. Lambs were fed a high-concentrate diet and supplemented with 0, 0.5, and 1% Gln on diet for 60 days. The experimental results show that the Gln treatment group had lower pepsin and cellulase enzyme activity, propionate acid concentration, and IL-6, TNF-α, claudin-1, and ZO-1 mRNA expression in the ruminal epithelium (p < 0.05); as well as increases in lipase enzyme activity, the ratio of propionic acid to acetic acid, the IL-10 content in the plasma, and the mRNA expression of IL-2 and IL-10 in the ruminal epithelium, in contrast to the CON (control group) treatment (p < 0.05). Taken together, the findings of this present study support the addition of Gln to improve digestive enzyme activity, the ruminal epithelium’s barrier, and fermentation and immune function by supplying energy to the mononuclear cells, improving the ruminal epithelium’s morphology and integrity, and mediating the mRNA expression of tight junction proteins (TJs) and cytokines.

Microbiota-gut-brain axis and nutritional strategy under heat stress

Heat stress is a very universal stress event in recent years. Various lines of evidence in the past literatures indicate that gut microbiota composition is susceptible to variable temperature. A varied microbiota is necessary for optimal regulation of host signaling pathways and disrupting microbiota-host homeostasis that induces disease pathology. The microbiota–gut–brain axis involves an interactive mode of communication between the microbes colonizing the gut and brain function. This review summarizes the effects of heat stress on intestinal function and microbiota–gut–brain axis. Heat stress negatively affects intestinal immunity and barrier functions. Microbiota-gut-brain axis is involved in the homeostasis of the gut microbiota, at the same time, heat stress affects the metabolites of microbiota which could alter the function of microbiota–gut–brain axis. We aim to bridge the evidence that the microbiota is adapted to survive and thrive in an extreme environment. Additionally, nutritional strategies for alleviating intestinal heat stress are introduced.

Effects of sodium humate and glutamine combined supplementation on growth performance, diarrhea incidence, blood parameters, and intestinal microflora of weaned calves

This experiment was conducted to investigate the effects of sodium humate (HNa) and glutamine (Gln) alone or combined supplementation on growth performance, diarrhea incidence, blood parameters, and intestinal microflora of weaned Holstein calves. In a 14-day experiment, 40 calves at 51 ± 3 days of age were randomly allocated to four treatment groups: (1) NC (basal diet), (2) NC + 5% HNa, (3) NC + 1% Gln, and (4) NC + 5% HNa + 1% Gln. Calves combined supplementation with HNa and Gln had a higher (P < .05) ADG, serum concentration of glucose (GLU), IgA, and IgG but lower fecal scores, diarrhea incidence, serum concentration of TNF-α, and IL-10 compared with NC group (P < .05). Compared with NC group, HNa + Gln group showed higher (P < .05) serum GSH and T-AOC activities but lower (P < .05) concentration of MDA and D-lac. Furthermore, the abundances of Prevotella ruminicola, Bifidobacterium, and Lactobacillus in rectal digesta were increased (P < .05), but the Escherichia coli was significantly decreased. In conclusion, combined supplementation with HNa and Gln can effectively improve the immune status, antioxidant capacity, and intestinal microflora of the weaned calves while reducing diarrhea incidence.

Glutamine supplementation affected the gut bacterial community and fermentation leading to improved nutrient digestibility in growth-retarded yaks

This study evaluated the effects of glutamine supplementation on nutrient digestibility, immunity, digestive enzyme activity, gut bacterial community and fermentation of growth-retarded yaks. A total of 16 growth-retarded yaks were randomly allocated to two groups: negative control (GRY) and glutamine supplementation group (GLN). Another eight growth-normal yaks were used as a positive control (GNY). Compared with GRY group, the crude protein digestibility was higher in GLN and GNY animals and the neutral detergent fiber digestibility was increased in GLN yaks. The concentrations of serum IgA, IgG, IgM and IL-10, as well as butyrate concentration and cellulase activity in the rumen and cecum were higher in GLN yaks compared to those in GRY animals. Supplementation with glutamine enhanced the chymotrypsin activity and increased the relative abundances of unclassified Peptostreptococcaceae and Romboutsia while decreased the relative abundances of unclassified Chitinophagaceae and Bacteroides in the jejunum and ileum of growth-retarded yaks. In the cecum, the relative abundance of unclassified Muribaculaceae was higher in GLN group than that in GRY group. The findings in this study suggest that the improved nutrient digestibility and immunity of growth-retarded yaks with glutamine supplementation may be through its potential impact on the lower gut host and microbial functions.

Bovine Immunology: Implications for Dairy Cattle

The growing world population (7.8 billion) exerts an increased pressure on the cattle industry amongst others. Intensification and expansion of milk and beef production inevitably leads to increased risk of infectious disease spread and exacerbation. This indicates that improved understanding of cattle immune function is needed to provide optimal tools to combat the existing and future pathogens and improve food security. While dairy and beef cattle production is easily the world's most important agricultural industry, there are few current comprehensive reviews of bovine immunobiology. High-yielding dairy cattle and their calves are more vulnerable to various diseases leading to shorter life expectancy and reduced environmental fitness. In this manuscript, we seek to fill this paucity of knowledge and provide an up-to-date overview of immune function in cattle emphasizing the unresolved challenges and most urgent needs in rearing dairy calves. We will also discuss how the combination of available preventative and treatment strategies and herd management practices can maintain optimal health in dairy cows during the transition (periparturient) period and in neonatal calves.

Dietary supplementation with glutamine improves gastrointestinal barrier function and promotes compensatory growth of growth-retarded yaks

The growth retardation of yaks commonly exists on the Tibetan Plateau, and the gastrointestinal barrier function of growth-retarded yaks is disrupted. Glutamine (Gln) is an effective feed additive to improve the gastrointestinal barrier function of animals. This research evaluated the effects of Gln on growth performance, serum permeability parameters, gastrointestinal morphology and barrier function of growth-retarded yaks. Thirty-two male growth-retarded yaks (74.0 ± 6.16 kg of BW and 480 ± 5.50 days of age) were randomly allocated to 4 groups: the negative control (GRY, fed basal ration), Gln1 (fed basal ration and 60 g/d Gln per yak), Gln2 (120 g/d) and Gln3 (180 g/d). Another 8 male growth normal yaks (112 ± 6.11 kg of BW and 480 ± 5.00 days of age) with same breed were used as a positive control (GNY, fed basal ration). The results showed that GRY had lower growth performance and higher (P < 0.05) diamine oxidase, D-lactic acid and lipopolysaccharide concentrations in serum as compared to GNY. Glutamine improved the average daily gain (ADG) of growth-retarded yaks, and the Gln2 group displayed highest ADG. Glutamine supplementation reduced markers of gut permeability in growth-retarded yaks. The GRY and Gln2 groups were selected to study the gastrointestinal barrier function. Growth-retarded yaks fed Gln2 showed higher (P < 0.05) height and surface area of ruminal papillae as compared to GRY. A similar trend of height and surface area in jejunal villus was found between GRY and Gln2 groups. The Gln2 increased (P < 0.05) the concentrations of secretory immunoglobulin A in jejunum and ileum of growth-retarded yaks. The rumen and jejunum of Gln2 yaks exhibited lower (P < 0.05) interleukin-1β and higher (P < 0.05) interleukin-10 mRNA expressions. Growth-retarded yaks fed Gln2 increased (P < 0.05) the expressions of claudin-1, occludin and zonula occludens-1 in the rumen and jejunum. In conclusion, dietary supplementation with Gln could improve the gastrointestinal barrier function and promote the compensatory growth of growth-retarded yaks.

Glucose Metabolism and Dynamics of Facilitative Glucose Transporters (GLUTs) under the Influence of Heat Stress in Dairy Cattle

Heat stress is one of the main threats to dairy cow production; in order to resist heat stress, the animal exhibits a variety of physiological and hormonal responses driven by complex molecular mechanisms. Heat-stressed cows have high insulin activity, decreased non-esterified fatty acids, and increased glucose disposal. Glucose, as one of the important biochemical components of the energetic metabolism, is affected at multiple levels by the reciprocal changes in hormonal secretion and adipose metabolism under the influence of heat stress in dairy cattle. Therefore, alterations in glucose metabolism have negative consequences for the animal’s health, production, and reproduction under heat stress. Lactose is a major sugar of milk which is affected by the reshuffle of the whole-body energetic metabolism during heat stress, contributing towards milk production losses. Glucose homeostasis is maintained in the body by one of the glucose transporters’ family called facilitative glucose transporters (GLUTs encoded by SLC2A genes). Besides the glucose level, the GLUTs expression level is also significantly changed under the influence of heat stress. This review aims to describe the effect of heat stress on systemic glucose metabolism, facilitative glucose transporters, and its consequences on health and milk production.

Safety and efficacy of l-glutamine produced using Corynebacterium glutamicum NITE BP-02524 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of l-glutamine (≥ 98.0%) produced by fermentation using a genetically modified strain of Corynebacterium glutamicum (NITE BP-02524). It is intended to be used in feed for all animal species and categories as nutritional additive (amino acid) and as sensory additive (flavouring compound). Viable cells of the production strain and its recombinant DNA were not detected in the additive. l-Glutamine manufactured by fermentation using C. glutamicum NITE BP-02524 does not give rise to any safety concern with regard to the genetic modification of the production strain. The use of l-glutamine produced by fermentation using C. glutamicum NITE BP-02524 in animal nutrition is considered safe for all animal species when applied as a nutritional additive to achieve an adequate amino acid profile in feed and to overcome potential glutamine shortages during critical periods of life. The proposed use level (25 mg/kg feed) when used as sensory additive (flavouring compound) is safe for all animal species. The uses of l-glutamine produced using C. glutamicum NITE BP-02524 as nutritional additive or as flavouring compound are considered safe for the consumer. l-Glutamine produced using C. glutamicum NITE BP-02524 is not toxic by inhalation, is non-irritant to skin and eyes and is not a skin sensitiser. l-Glutamine produced using C. glutamicum NITE BP-02524 is considered safe for the environment. l-glutamine is a non-essential amino acid and it plays a physiological role as such. Recent evidence shows that glutamine may act as conditionally essential amino acid mainly in growing animals and has some specific effects e.g. in improving intestinal development and immune response. This amino acid produced by fermentation using C. glutamicum NITE BP-02524 is regarded as an efficacious source of glutamine for all animal species. For supplemental l-glutamine to be as efficacious in ruminants as in non-ruminants, it would require protection against degradation in the rumen. The use of l-glutamine as sensory additive at 25 mg/kg feed is considered efficacious.

Invited review: Management strategies capable of improving the reproductive performance of heat-stressed dairy cattle

Impaired fertility during periods of heat stress is the culmination of numerous physiological responses to heat stress, ranging from reduced estrus expression and altered follicular function to early embryonic death. Furthermore, heat-stressed dairy cattle exhibit a unique metabolic status that likely contributes to the observed reduction in fertility. An understanding of this unique physiological response can be used as a basis for improving cow management strategies, thereby reducing the negative effects of heat stress on reproduction. Potential opportunities for improving the management of dairy cattle during heat stress vary greatly and include feed additives, targeted cooling, genetic selection, embryo transfer and, potentially, crossbreeding. Previous studies indicate that dietary interventions such as melatonin and chromium supplementation could alleviate some of the detrimental effects of heat stress on fertility, and that factors involved in the methionine cycle would likely do the same. These supplements, particularly chromium, may improve reproductive performance during heat stress by alleviating insulin-mediated damage to the follicle and its enclosed cumulus-oocyte complex. Beyond feed additives, some of the simplest, yet most effective strategies involve altering the timing of feeding and cooling to take advantage of comparatively low nighttime temperatures. Likewise, expansion of cooling systems to include breeding-age heifers and dry cows has significant benefits for dams and their offspring. More complicated but promising strategies involve the calculation of breeding values for thermotolerance, the identification of genomic markers for heat tolerance, and the development of bedding-based conductive cooling systems. Unfortunately, no single approach can completely rescue the fertility of lactating dairy cows during heat stress. That said, region-appropriate combinations of strategies can improve reproductive measures to reasonable levels.

Metabolomics Reveals that Crossbred Dairy Buffaloes Are More Thermotolerant than Holstein Cows under Chronic Heat Stress

Heat stress (HS) threatens the worldwide dairy industry by decreasing animal production performance and health. Holstein cows and dairy buffaloes are the most important dairy animals, but their differences in the metabolic mechanism of thermotolerance remain elusive. In this study, we used serum metabolomics to evaluate the differences in thermotolerance between Holstein cows and crossbred dairy buffaloes under chronic heat stress (HS) and thermal-neutral conditions. In response to HS, the body temperatures and respiratory rates were increased more for Holstein cows than for dairy buffaloes (38.78 vs 38.24 °C, p < 0.001; 43.6 vs 32.5 breaths/min, p < 0.001). HS greatly affected serum metabolites associated with amino acids, fatty acids, and bile acids. The enriched metabolic pathways of these serum metabolites are closely related to HS. We demonstrated that buffaloes adapt to HS by adopting a metabolism of branched-chain amino acids and ketogenic amino acids and gluconeogenesis, but Holstein cows decrease the effect of HS with citrulline and proline metabolism. Both physiological parameters and serum metabolic profiles indicate that dairy buffaloes are more thermotolerant than Holstein cows, providing the feasibility to vigorously develop the buffalo dairy industry in tropical and subtropical regions.

Heat stress: impact on livestock well-being and productivity and mitigation strategies to alleviate the negative effects

Heat stress (HS) is a multi-factorial problem that negatively affects livestock health and productivity and is closely linked with animal welfare. While HS may not be harmful when animals are able to adapt, the physiological changes that occur to ensure survival may impede the efficient conversion of feed energy into animal products. This adaptive response can be variable and is often based on previous HS exposure, genetics, species and production stage. When the heat load becomes too great for adaptive responses to compensate, the subsequent strain response causes reduced productivity and well-being and, in severe cases, mortality. The effects of HS on livestock productivity are well documented and range from decreased feed intake and body weight gain, to reduced reproductive efficiency and altered carcass composition and meat quality. In addition, researchers are beginning to elucidate the effects of prenatal HS on postnatal livestock performance and welfare. As knowledge of the negative impacts of HS on livestock performance and welfare increases, so will the development of effective mitigation strategies to support maintenance of productivity during times of high thermal heat loads and preserve appropriate animal welfare standards.

Integrated Metabolomics Study of the Milk of Heat-stressed Lactating Dairy Cows

Heat stress (HS) damages the global dairy industry by reducing milk yields and quality, harming health, and damaging the reproduction of dairy cows, causing huge economic losses each year. However, an understanding of the physiological mechanism of HS lactating dairy cows remains elusive. Here, a metabolomics study using LC-MS and ¹H NMR spectroscopy was performed to analyze the metabolomic differences in the milk between HS-free and HS dairy cows, and discover diagnostic biomarkers and changes in the metabolic pathway. A total of 53 discriminating metabolites were significantly up- or down-regulated in the HS group compared with the HS-free group (P < 0.05). These biomarkers were involved in pathways of carbohydrate, amino acid, lipid, and gut microbiome-derived metabolism. Comparing these potential biomarkers with previously identified HS candidate biomarkers in plasma, significant correlations between the levels of lactate, pyruvate, creatine, acetone, β-hydroxybutyrate, trimethylamine, oleic acid, linoleic acid, lysophosphatidylcholine 16:0, and phosphatidylcholine 42:2 in milk and plasma were found, indicating that the blood-milk barrier became leaky and the levels of these 10 biomarkers in milk can reflect HS-induced metabolomic alterations in blood. These novel findings can support more in-depth research to elucidate the milk-based changes in metabolic pathways in HS lactating dairy cows.

Glucagon-like peptide-2 and intestinal mucosal immunity

Glucagon-like peptide-2 (GLP-2) is a single chain polypeptide hormone with a molecular weight of 3.9 kDa, which is secreted by L cells of the intestine. GLP-2 is a specific intestinal epithelial growth factor, and it can promote the repair of intestinal mucosa injury, inhibit apoptosis, improve the intestinal absorption of nutrients, and strengthen the intestinal barrier function. GLP-2 also plays an important role in maintaining the continuity and integrity of the intestinal mucosa. These characteristics make GLP-2 become the current research hotspot in the field of gastrointestinal barrier function. The main focus of previous studies is on nutrient absorption and protection of the intestinal mechanical barrier, and there have been relatively scarce studies on the protective effect of GLP-2 on intestinal mucosal immune barrier. This article reviews the role of GLP-2 in intestinal mucosal immunity and the possible mechanisms.

Aging influences the response of T cells to stimulation by the ellagitannin, oenothein B

Several plant extracts, including certain polyphenols, prime innate lymphocytes and enhance responses to secondary stimuli. Oenothein B, a polyphenol isolated from Epilobium angustifolium and other plant sources, enhances IFNγ production by both bovine and human NK cells and T cells, alone and in response to secondary stimulation by cytokines or tumor cells. Innate immune cell responsiveness is known to be affected by aging, but whether polyphenol responses by these cells are also impacted by aging is not known. Therefore, we examined oenothein B responsiveness in T cells from cord blood, young, and adult donors. We found that oenothein B stimulates bovine and human T cells from individuals over a broad range of ages, as measured by increased IL-2Rα and CD69 expression. However, clear differences in induction of cytokine production by T cells were seen. In T cells from human cord blood and bovine calves, oenothein B was unable to induce IFNγ production. However, oenothein B induced IFNγ production by T cells from adult humans and cattle. In addition, oenothein B induced GM-CSF production by human adult T cells, but not cord blood T cells. Within the responsive T cell population, we found that CD45RO+ memory T cells expressed more cytokines in response to oenothein B than CD45RO- T cells. In summary, our data suggest that the immunostimulation of T cells by oenothein B is influenced by age, particularly with respect to immune cytokine production.

Heat-tolerant versus heat-sensitive Bos taurus cattle: influence of air temperature and breed on the acute phase response to a provocative immune challenge

The difference in the acute phase response of a heat-tolerant and a heat-sensitive Bos taurus breed to a lipopolysaccharide (LPS) challenge when housed at different air temperatures (Ta) was studied. Angus (ANG; heat-sensitive; n = 11; 306 ± 26 kg BW) and Romosinuano (RO; heat-tolerant; n = 10; 313 ± 32 kg BW) heifers were transported from the USDA Agricultural Research Service SubTropical Agricultural Research Station in Florida to the Brody Environmental Chambers at the University of Missouri, Columbia. Heifers were housed in stanchions in 4 temperature-controlled environmental chambers. Initially, Ta in the 4 chambers was cycling at thermoneutrality (TN; 18.5°C-23.5°C) for a 1-wk adjustment period, followed by an increase in 2 of the 4 chambers to cycling heat stress (HS; 24°C-38°C) for 2 wk. On day 19, heifers were fitted with jugular catheters and rectal temperature (RT) recording devices. On day 20, heifers were challenged with LPS (0.5 μg/kg BW; 0 h), sickness behavior scores (SBSs) were recorded, and blood samples were collected at 0.5-h intervals from -2 to 8 h and again at 24 h relative to LPS challenge at 0 h. Serum was isolated and stored at -80°C until analyzed for cortisol and cytokine concentrations. A breed by Ta interaction (P < 0.001) was observed for RT such that the post-LPS average RT in RO heifers housed at TN was lower than the RT of all other treatment groups (P < 0.001), whereas ANG heifers housed at HS had greater post-LPS average RT than all other treatment groups (P < 0.001). In response to LPS, HS increased SBS after LPS in RO heifers compared to RO heifers housed at TN (P < 0.001), whereas HS decreased SBS after LPS in ANG heifers compared to ANG heifers housed at TN (P = 0.014). The cortisol response to LPS was greater in TN than in HS heifers (P < 0.01) and was also greater in RO than in ANG heifers (P = 0.03). A breed by Ta interaction (P < 0.01) was observed for tumor necrosis factor-α (TNF-α) concentration such that HS increased post-LPS serum concentrations of TNF-α in ANG heifers compared to ANG heifers housed at TN (P = 0.041), whereas HS decreased post-LPS concentrations of TNF-α in RO heifers compared to RO heifers housed at TN (P = 0.008). A tendency (P < 0.06) was observed for a breed by Ta interaction for IL-6 concentrations such that RO heifers had greater post-LPS concentrations of IL-6 than ANG heifers when housed at HS (P = 0.020). A breed by Ta interaction was observed for interferon-γ (IFN-γ; P < 0.01) concentrations such that HS decreased post-LPS concentrations of IFN-γ in ANG heifers compared to ANG heifers housed at TN (P < 0.001), and HS increased post-LPS concentrations of IFN-γ in RO heifers compared to RO heifers housed at TN (P = 0.017). These data indicate differences in the acute phase response between the heat-tolerant RO and heat-sensitive ANG heifers under different Ta which may aid in elucidating differences in productivity, disease resistance, and longevity among cattle breeds.