Optimization of Marbling Through Vitamin A Management at Different Stages of Production Cycle in Beef Cattle

In pregnant and lactating cows

The cow-calf operation is the first stage in the beef cattle production system. Profitability of the cow-calf operation greatly depends on the reproductive efficiency of cows and the growth efficiency of calves. Because muscle development and intramuscular adipocyte formation are actively ongoing, the prenatal stage, especially the mid to late fetal stage, is critical for enhancing offspring productivity (Du et al., 2013). Maternal nutritional status at this stage greatly influences the offspring’s myogenesis, fibrogenesis, and adipogenesis (Hossain et al., 2025; Hossain et al., 2024). By regulating the proliferation and lineage-specific differentiation of progenitor cells, vitamin A is essential for the maintenance and formation of numerous tissues, including adipose tissue, skeletal muscle, and immune cells (Alosilla et al., 2007; Du, 2023; Jin et al., 2024). Beef production depends heavily on pastures, and the quality and quantity of grass in the pasture depend on the weather and geographical location. In the yearly reproduction cycle of cattle, pregnant cows frequently experience vitamin A deficiency, which occurs due to no or few availability of fresh forage during the winter and early spring, profoundly limiting β-carotene intake, and the increased nutrient demands due to the rapidly growing fetuses during the mid to late gestation (Weiss, 2018), which completely rely on maternal circulation for retinol (Sapin et al., 2000; Spiegler et al., 2012). Calves born to a vitamin A-deficient dam have low liver retinol storage and compromised immune functionality (Spiegler et al., 2012). Vitamin A supplementation to dams robustly enhances immune response and antibody concentration in offspring (Palmer et al., 2015).

While studies about vitamin A supplementation for beef cows are limited, there are several studies in dairy cows. To meet vitamin A demands, a supplementation of 110 IU/kg body weight is recommended for lactating dairy cows, or approximately 75,000 IU/day for a cow producing 75lb milk/day and consuming 60% forage with little or no fresh forage ( NRC, 2001). The vitamin A supplementation during the dry period increases plasma retinol concentrations of calves and retinol concentration in the first colostrum (Puvogel et al., 2008). For cows producing over 75lb of milk, an additional supplementation of 450 IU/lb of milk can recover the loss of vitamin A via milk (according to the National Academies of Sciences, Engineering, and Medicine (NASEM), 2021). At the start of lactation, there is a significant loss of plasma retinol via colostrum; however, there is insufficient data about the requirement for additional vitamin A supplementation during this period.

In neonate calves

Neonatal calves have a greater risk of deficiency relative to cows, as they are born with low liver retinol storage (Speer et al., 2024; Zanker et al., 2013). The critical role of retinoic acid in immune system development has been well established (West et al., 1989). Calf born with vitamin A deficiency have enhanced susceptibility to respiratory disease and calf scour due to immune deficiency (McGill et al., 2019). In humans, vitamin A supplementation remains widely used in developing countries to reduce the incidence of diarrhea and respiratory diseases in offspring (Imdad et al., 2011; Lie et al., 1993; Sommer et al., 1986). In addition to immune function, vitamin A plays a crucial role in vision. Lower vitamin A is associated with impaired weight gain, exophthalmos, and blindness in calves (Kang et al., 2017; van der Lugt and Prozesky, 1989). Altered skeletal growth was reported in a vitamin A-deficient calf (Gallina et al., 1970). Major skeletal growth occurs during the early stage of life, and vitamin A assists in bone development by stimulating the proliferation of osteoblasts and bone resorption (Yee et al., 2021). Early vitamin A deficiency manifests as staggering gait, lameness or stiffness in joints, swelling of legs and brisket (Olson and Hollis, 2007). Taking these immune and developmental functions into consideration, vitamin A deficiency can result in serious health outcomes as well as impaired growth.

Colostrum is the primary source of vitamin A. In addition, liver storage and plasma retinol concentrations rapidly increase in neonatal calves after intake of the first colostrum (Puvogel et al., 2008). For the first 2 to 3 mos of extrauterine life, calves depend greatly on the quality and quantity of colostrum that they absorbed in the first day of life to train their nascent immune system (Nowak et al., 2012; Osorio et al., 2013). Calves born with an adequate level of vitamin A acquire additional vitamin A from colostrum to meet calves’ requirements (NASEM, 2021). However, calves with a deficient vitamin A level can be supplemented with a 5,000,000 IU vitamin A injection for an initial boost to retinol level. Liver or plasma retinol level should be assessed before injection to avoid hypervitaminosis and associated impairment of bone growth (Woodard et al., 1997). The NASEM recommendation for calves receiving milk replacer is 11,000 IU/kg milk replacer till the age of 3 mos, and calves on dry starter feed is 3,700 IU/kg DM (NASEM, 2021). However, calves born with severe developmental deformities, with muscle incoordination, will not be reversed by vitamin A supplementation.

Feeder cattle undergo a critical transition process from pasture to a grain-based diet in a feedlot specially in the first 3 to 4 wks. Vitamin A deficiency may develop after the feeder calves are on a ration containing adequate retinol or vitamin A, due to replacing yellow corn with grain containing lower β-carotene, entering feedlot from winter pasture, using younger animals with lower liver retinol storage, or grazing on forages with drought or excessive use of nitrogen fertilizer (Mitchell et al., 1967). Younger animals deplete their liver storage more easily and are more likely to express the deficiency symptoms sooner than the older animals when on a vitamin A–deficient diet (Wellmann et al., 2020). Cattle with vitamin A deficiency exhibit reduced feed intake, poor weight gain, ataxia, convulsions, rough and dull hair coat, hair loss, and scale or scurf on the skin, night blindness, and total blindness in young and growing animals (Booth et al., 1987). For growing cattle, the requirement of vitamin A is 3,700 IU/kg of DM (NASEM, 2021). Incoming feeders and growing cattle under stress or coming from winter pasture can be supplemented with 500,000 to 1 million IU vitamin A via intramuscular, intra-ruminal injection or via drinking water to recover from the deficiency. However, monitoring plasma retinal level or liver storage by biopsy is required for the early identification of deficiency and timely vitamin A supplementation.

In finishing cattle, studies focused on vitamin A restriction due to its role in enhancing lipid oxidation. However, the NESAM recommendation of vitamin A for finishing cattle is 2,200 IU/kg DM, and cattle maintained on this recommended level of vitamin A supplementation exhibited higher average daily gain compared to those fed 3 and 5 times higher supplementation or completely vitamin A-restricted cattle (Gorocica-Buenfil et al., 2007; Pyatt et al., 2005; Zinn et al., 1996). On the other hand, finishing cattle without vitamin A supplementation for 120 d didn’t exhibit symptoms of night blindness or other complications and showed no alteration in carcass characteristics (Bryant et al., 2010; Wellmann et al., 2020). These data suggest the relatively higher tolerance of finishing cattle compared to young calves to vitamin A deficiency.

Origins and timeline of adipocyte formation in different fat depots of beef cattle

The development of visceral, subcutaneous, intermuscular, and intramuscular fat depots begins at different time points of the embryonic and fetal stages. During early development, somites, the segmented structures of embryos, split into sclerotomes and dermomyotomes around gestational day (GD) 20. The dermomyotomes further develop into myogenic and nonmyogenic multipotent progenitor cells at approximately GD 30 in beef cattle (Du et al., 2017). The visceral adipose tissue progenitor cells and preadipocytes are the first to appear, mainly from non-myogenic cells of the dermomyotome at GD 80 (Du, 2023; Vernon, 1986). The de novo formation of new adipocytes in visceral fat continues during the neonatal stage. The subcutaneous and intermuscular adipocytes appear following the visceral depot, and their formation continues until the early preweaning period, after which it becomes progressively limited (Figure 1) (Keogh et al., 2021). The intramuscular adipocytes are the last ones to appear at approximately GD 180 of the fetal stage and continue till about 250 d of age, when it wanes (Du, 2023).

Figure 1.

Timeline of intramuscular, visceral, subcutaneous, and intermuscular fat development in Angus cattle. The times for adipocyte hyperplasia and hypertrophy are approximate (Du, 2023; Du et al., 2017; Keogh et al., 2021; Vernon, 1986). NT: notochord; DM: dermomyotome; GD: gestation days; IMF: intramuscular fat. Created with BioRender.com

Proliferation and adipogenic differentiation of progenitor cells

The formation of new adipocytes occurs through 2 distinct phases: commitment of progenitor cells to adipogenic lineage and differentiation of committed cells into mature adipocytes (Nguyen et al., 2021). The sequential expression of several transcription factors and lineage-specific genes regulates adipogenic commitment of mesenchymal progenitor cells, followed by the differentiation process. The proliferation and pluripotency of these mesenchymal progenitor cells are regulated by several transcription factors, including Krüppel-like factor 2 (KLF2), SRY-related HMG-box 9 (SOX9), and preadipocyte factor 1 (PREF-1) (Table 1). They express highly in undifferentiated embryonic stem cells and promote their proliferation. The higher abundance of progenitor cells allows the formation of more adipocytes in the later stages of life. The expression Klf2 downregulates during differentiation, accompanied by loss of cell pluripotency (da Silva et al., 2020; Sun et al., 2022; Vietor et al., 2023; Wang et al., 2016b).

Zinc-finger protein 423 (ZFP423) is the first transcription factor expressed during the commitment of progenitor cells to adipogenesis. In bovine stromal vascular cells, Zfp423 expression correlates with their adipogenic potential (Gupta et al., 2012; Hepler et al., 2017; Huang et al., 2012). In the same steer, Zfp423 expression varies across different muscles and was correlated with the IMF abundance (Martinez Del Pino et al., 2020). These findings suggest Zfp423 as a regulator of muscle-specific differences in adipogenic potential.

The further differentiation of committed adipocytes is mediated by a cascade of adipogenic regulatory factors, including CCAAT/enhancer-binding proteins (C/EBPs) family and peroxisome proliferator-activated receptor γ (PPARγ) (Park et al., 2016; Tang et al., 2021). C/EBPβ and C/EBPδ appear during the early stage of adipogenesis and form a heterodimer complex that induces the expression of the terminal differentiation marker Pparγ and Cebpα (Table 1) (Malibary, 2023; Park et al., 2016). PPARγ also enhances Cebpα expression to facilitate the terminal differentiation of adipocytes (Rosen et al., 1999). In addition, sterol regulatory element-binding protein 1c (SREBP1C) is another crucial regulatory factor of adipogenic differentiation, which is induced by the C/EBPβ and C/EBPδ dimer and enhances the formation of PPARγ ligands, which facilitates the terminal differentiation of adipocytes (Payne et al., 2009; Wang et al., 2016a). Collectively, adipocyte differentiation is a complex and highly coordinated process involving multiple transcription factors that interact, regulate one another, and fine-tune each other’s activity.

Regulation of lipid accumulation in adipocytes

Following adipogenic differentiation, adipocytes accumulate lipids to increase in size, a process referred to as adipocyte hypertrophy. This accumulation occurs by the uptake of free fatty acids that are released from the circulating lipoprotein by lipoprotein lipase and by de novo fatty acid (FA) synthesis inside adipocytes (Goldberg et al., 2009). Fatty acid translocase (CD36), fatty acid transporter protein 1 (FATP1), and intercellular fatty acid binding protein 4 (FABP4) are involved in the transportation of FA into adipocytes (Table 1) (Goszczynski et al., 2017; H. Li et al., 2022). The Fabp4 abundance is correlated with IMF deposition and cattle breeds such as Wagyu, renowned for their high IMF, which highly express this gene (Goszczynski et al., 2017). During de novo FA synthesis, acetyl-CoA carboxylase converts acetyl-CoA to malonyl-CoA, which is then used for fatty acid chain elongation by fatty acid synthase. Stearoyl-CoA desaturase (SCD) subsequently introduces double bonds into saturated fatty acyl chains to produce monounsaturated fatty acids. Esterification of these FA with glycerol backbone forms triacylglycerol (TAG), the neutral lipid stored as lipid droplets inside adipocytes (Xue et al., 2017). Adipocytes in ruminants can effectively utilize acetate as a substrate to synthesize fatty acids (Nguyen et al., 2021). Glucose transporter 4 (GLUT4), an insulin-dependent glucose transporter, facilitates the uptake of glucose into cells, and glucose is used for producing the glycerol backbone. Importantly, propionic acid produced during rumen fermentation is a major source of glycerol for TAG synthesis in cattle (Maldini and Allen, 2019). Once TAG is formed, perilipin-1 (PLIN1) coats the lipid droplets to make them stable inside adipocytes. On the other hand, lipolysis, catalyzed by hormone-sensitive lipase, hydrolyzes TAG and releases FFA and glycerol. Then, FFA is broken down into acetyl-CoA in mitochondria for β-oxidation and energy production (Houten and Wanders, 2010).

Greater IMF deposition is correlated with the higher capability of synthesizing saturated fatty acids and monounsaturated fatty acids (MUFA) in cattle (Nguyen et al., 2021). Stearoyl-CoA desaturase catalyzes the synthesis of MUFA, a major component of IMF, which enhances beef flavor (Oh et al., 2013). Cattle such as Wagyu and Hanwoo that exhibit higher IMF compared to Angus, Holstein, and other beef breeds highly express Scd (Gotoh and Joo, 2016), which catalyzes MUFA production (Chung et al., 2021). In addition, MUFA can act as a PPARγ ligand and enhance PPARγ activity (Moreno et al., 2010), which likely can promote adipogenesis.

Vitamin A promotes the proliferation of adipogenic progenitor cells

Retinoic acid, the active metabolite of vitamin A, is a major regulator of adipogenesis. Retinoic acid binds to retinoic acid receptor (RAR) and retinoic acid X receptor, which form a dimer and bind with specific retinoic acid response elements located in the promoters of their target genes (Cunningham and Duester, 2015; Malibary, 2023). Retinoic acid regulates adipogenesis by influencing cellular differentiation, proliferation, and lipid accumulation; however, its regulatory effects and outcomes vary depending on the stage of adipogenic development.

As a potent regulator, retinoic acid regulates the proliferation and commitment of progenitor cells. In adipogenic progenitor cells, Pref1 and Klf2 expression increase shortly after retinoic acid exposure (Jin et al., 2024). Retinoic acid upregulates Pref-1 expression by activating the cellular retinoic acid binding protein type II (CRABP-II)/ RARγ (Noy, 2013). Another gene, Sox9, is a downstream target of PREF-1 become activated after retinoic acid exposure. By activating Sox9 and Klf2, Retinoic acid enhances progenitor cell proliferation and expands the progenitor cell pool (Berry et al., 2012). Retinoic acid-mediated expansion of the progenitor cell population during the embryonic stage may increase the number of cells available for differentiation later in development (Figure 2).

Figure 2.

Potential role of retinoic acid on adipocyte hyperplasia and hypertrophy at different stages of development in beef cattle. Both hyperplasia and hypertrophy are continuous processes, and the hypothetical timeline only shows the dominant mechanism at that stage (Ayala-Sumuano et al., 2016; Berry et al., 2012; Harris et al., 2018; Huang et al., 2012; Jin et al., 2024; Lim et al., 2006; Tourniaire et al., 2015; Xie et al., 2020). KLF2: Krüppel-like factors-2; SOX9: SRY-related HMG-box 9; PREF-1: Preadipocyte factor 1; ZFP423: Zinc-finger protein 423; C/EBP: CCAA T/enhancer-binding proteins, PPARγ: peroxisome proliferator-activated receptor γ; CD36: Fatty acid translocase. Created with BioRender.com

Vitamin A enhances adipogenic commitment

As a key developmental gene, Zfp423 is highly expressed in committed adipogenic progenitor cells in both rodents and cattle (Gupta et al., 2012; Harris et al., 2018; Huang et al., 2012; Jin et al., 2024). In vivo retinoic acid treatment in adipogenic progenitor cells initially increased cell proliferation and Zfp423 expression, but its expression downregulated with the progression of differentiation (Hepler et al., 2017; Jin et al., 2024; Wang et al., 2017). As Zfp423 is expressed in the very early stage of adipogenesis during commitment, the early upregulation enhances the adipogenic commitment and downregulates with the advancement of adipogenesis, likely due to retinoic acid-mediated inhibition of differentiation (Berry et al., 2012). Collectively, these data indicate the positive effects of vitamin A on Zfp423 expression and adipogenic commitment.

Vitamin A inhibits adipogenic differentiation

Transcription factors PPARγ and CEBPα are two master regulators of adipogenic differentiation, preceded by early differentiation marker C/EBPβ. Retinoic acid signaling suppresses the expression of both early and terminal differentiation markers. Retinoic acid upregulates SMAD3, the downstream of transforming growth factor (TGF) β signaling pathway, which alters the DNA binding ability of C/EBPβ through its Mad homology 1 (MH1) domain (Hossain et al., 2024; Marchildon et al., 2010). Retinoic acid inhibits the GSK3β-mediated phosphorylation activity at Thr188 of C/EBPβ and decreases its DNA binding capability (Ayala-Sumuano et al., 2016; X. Li et al., 2009). Downregulation of C/EBPβ delays the expression of terminal differential regulators Pparγ and Cebpα, inhibiting adipogenic differentiation (Guo et al., 2015). In addition, retinoic acid can directly inhibit PPARγ and CEBPα activity. In vivo retinoic acid treatment induces the expression of Fos-related antigen 1 (FRA1) that directly binds with the Pparγ promoter to downregulate its expression (Xie et al., 2020). In addition, C/EBP homologous protein (CHOP) is upregulated in preadipocytes after retinoic acid exposure. CHOP forms a heterodimer with C/EBPβ, sequestering its ability to stimulate C/EBPα expression and delay the terminal differentiation (Chikka et al., 2013; Gery et al., 2004). Thus, retinoic acid inhibits both early and late stages of adipogenic differentiation.

Vitamin A suppresses lipogenesis and enhances fatty acid oxidation

Retinoic acid suppresses lipogenesis and impairs adipocyte hypertrophy. Fatty acid translocation into cells is regulated by Cd36, the expression of which is stimulated by PPARγ, a key marker for terminal adipogenic differentiation (Lim et al., 2006). By inhibiting Pparγ expression, retinoic acid delays Cd36 expression, reduces fatty acid transport into mature adipocytes, and thereby suppresses lipogenesis (Amengual et al., 2018). In addition, retinoic acid promotes lipid catabolism and enhances energy expenditure in the body. Retinoic acid upregulates Pparα, a key gene promoting β-oxidation (Mandard et al., 2004). Retinoic acid also acts as a ligand for PPARβ/δ, further enhancing peroxisomal fatty acid β-oxidation (Levi et al., 2015; Shaw et al., 2003). In addition, retinoic acid activates transcription of Peroxisome-proliferator-activated receptor-γ coactivator-1 (PGC-1α), in coordination with PPARα, activates the other key genes, including Carnitine palmitoyl transferase 1A (CPA-1a), to upregulate β-oxidation (Song et al., 2010). Furthermore, retinoic acid enhances the browning of white adipose tissue by facilitating mitochondrial biogenesis and inducing Ucp1 expression (Tourniaire et al., 2015; Wang et al., 2017; Wang et al., 2018). Collectively, retinoic acid inhibits adipocyte hypertrophy through enhancing fatty acid β-oxidation and suppressing adipocyte hypertrophy.

To summarize, the impact of retinoic acid on adipose development is stage-specific. It enhances the proliferation and self-renewal of the adipogenic progenitor cells and commitment of preadipocytes; however, it inhibits differentiation and lipid accumulation (Figure 2).

Vitamin A management in late gestation

Adipocyte progenitor cells begin to appear in the intramuscular area during the mid to late gestation, around GD180, whereas in other fat depots they appear earlier (Figure 2) (Du, 2023). As discussed above, retinoic acid promotes the proliferation of adipogenic progenitor cells, which provides an opportunity to effectively increase the IMF progenitor cell pool with less effect on other depots. Consistently, retinoic acid treatment to Angus-Simmental cows from GD180 till parturition increased IMF deposition without a significant effect on the subcutaneous fat thickness and Kidney Pelvic Heart (KPH) fat (Table 2) (Sarah et al., 2024). On the other hand, retinoic acid treatment during this period didn’t affect muscle development (Sarah et al., 2024). In another study, retinoic acid treatment of Hanwoo cows from GD150 to parturition affected both myogenesis and intramuscular adipogenesis. The longissimus dorsi muscle showed higher expression of Klf2, indicating an increased proliferation rate of progenitor cells, as well as elevated expression of myogenic marker genes Myod and Myf5 (Jo et al., 2020). Since secondary myogenesis in beef cattle is actively ongoing around GD150, retinoic acid treatment during this period may enhance muscle development (Du et al., 2017). However, adipogenesis in subcutaneous, visceral, and intermuscular fat depots is also active during this time, meaning that retinoic acid treatment could potentially increase adipocyte progenitor cell population in these depots, a possibility that was not assessed in the study (Jo et al., 2020). Furthermore, because myogenic and adipogenic cells originate from the same progenitor pools, early embryonic retinoic acid treatment might shift the balance of progenitor cell fates toward myogenesis (Song et al., 2024). While the impact of this early retinoic acid treatment on final body weight and intramuscular fat content in finishing cattle needs to be thoroughly examined, available studies point to promising results. In Angus-Nellore cows, vitamin A treatment on GD 250 resulted in higher body weight and ribeye area. In addition, it increased both IMF percentage and backfat thickness, with steers surprisingly exhibiting greater improvements than heifers in all parameters (Ladeira et al., 2024). Therefore, vitamin A supplementation during the last trimester of gestation has the potential for enhancing IMF development, with steers showing a better response than heifers (Figure 3).

Figure 3.

Proposed vitamin A management windows to optimize intramuscular fat deposition in beef cattle. In the prenatal vitamin A supplementation window, vitamin A is supplemented at 12,200 IU/kg DM from GD180 to parturition (based on prenatal treatment on Angus x Simmental cows or neonatal injection of 150,000 IU/hd to calf at birth and 1 mo of age (Harris et al., 2018; Sarah et al., 2024; Yu et al., 2022)). During the vitamin A restriction window at the finishing stage, cattle are provided 600 to 1103 IU/kg DM vitamin A (Based on vitamin A restriction treatment of Angus x Simmental and Angus Steers for 5 and 10 mos, respectively, from Knutson et al., 2020; Kruk et al., 2018). GD: gestation day.

Note: High doses of vitamin A intake or injection during pregnancy may lead to teratogenic effects in offspring for both humans and animals (Rothman et al., 1995). Serum retinol level should be monitored, and animals with a serum retinol level lower than the minimum required level (22.5 ng/mL) should not enter vitamin A restriction treatment due to health complications of vitamin A deficiency.

Vitamin A management in the neonatal stage

The hyperplasia of intramuscular adipocytes continues after birth until approximately 250 d of age, whereas the hyperplasia of other fat depots gradually declines after the neonatal stage (Du et al., 2017). Therefore, retinoic acid treatment of calves in the neonatal stage has been used as a strategy to improve IMF content in beef. In Angus steer calves, vitamin A injection of 150,000 IU administered twice at birth and at one month of age increased IMF by approximately 18–24%, along with marbling score, without altering other fat depots at 438 d of age, and showed greater efficiency than a 300,000 IU injection (Table 3) (Harris et al., 2018; Yu et al., 2022). Biceps femoris muscle at 2 mos of age from vitamin A-treated calves exhibited increased population of adipose tissue Pdgfrα positive adipose progenitor cells, as well as an upregulation of angiogenic genes Vegfa and Vegfr2. Similarly, intramuscular injection of vitamin A in Montana-Nellore calves resulted in a ∼25.4% increase in IMF in the longissimus thoracis muscle without alteration in body weight and ribeye area (Maciel et al., 2022). Additionally, combined vitamin A treatment during late pregnancy and the neonatal stage in Hanwoo cattle increased body weight gain and the expression of the preadipogenic marker gene Pref1, indicating a potential increase in adipogenic progenitor population and yield in finishing cattle (Peng et al., 2020). However, in this study, the final IMF percentage and carcass weight of the cattle were not evaluated. Overall, these findings suggest that vitamin A treatment during the neonatal stage, alongside prenatal administration, can be effective in enhancing IMF in beef cattle.

Comparing vitamin A treatment during prenatal and neonatal stages provided important insights into the relative effectiveness of vitamin A treatment. Vitamin A treatment in cows during the last month of pregnancy, compared to treatment of calves at birth and 2 mos of age, revealed that prenatal administration resulted in greater increases in IMF percentage and ribeye area in steers than neonatal treatment (Ladeira et al., 2024). However, vitamin A treatment at either stage did not result in differences in final body weight or dressing percentage among steers. While neonatal vitamin A treatment produced a ∼18–25.4% increase in IMF in carcasses, prenatal supplementation to cows achieved a substantial ∼41% increase (Maciel et al., 2022; Sarah et al., 2024; Yu et al., 2022). Overall, evidence suggests that both prenatal and neonatal vitamin A treatments can improve IMF in beef cattle without increasing the mass of other fat depots or negatively impacting growth performance and carcass yield, while prenatal treatment during the last trimester (GD180 to parturition) can be more effective.

Vitamin A management in growing and finishing heifers and steers

During the growing and finishing stages, the adipogenic capacity of the intramuscular fat depot wanes, and lipid accumulation in existing adipocytes becomes a major factor in marbling fat accumulation. While vitamin A supplementation during early developmental stages increases IMF adipocyte number, which provides sites for marbling fat deposition, vitamin A during the growing and finishing stages enhances lipid oxidation to suppress marbling fat accumulation. Therefore, vitamin A restriction has been used to increase IMF deposition, particularly in steers (Table 4) (Knutson et al., 2020; Kruk et al., 2018; Pickworth et al., 2012a; Wellmann et al., 2020).

The recommended level of vitamin A by the NASEM is 2,000 IU/Kg DM (NASM, 2016) for feedlot cattle. Supplementation of vitamin A to the recommended level or higher level (11,000 IU/kg DM) in vitamin A-depleted steers for a shorter period of time during the finishing stage in 7 to 8-mo-old Angus cattle didn’t impact the carcass yield or quality, including IMF, KPH, and marbling score (Wellmann et al., 2020). However, supplementation for a long time (∼10 mos) in Angus reduced IMF percentage and backfat thickness, without reducing the density of adipocytes (Kruk et al., 2018; Pickworth et al., 2012a). In yearling and 2-year-old Limousin-Luxi cattle, a higher dose of vitamin A (4,000 IU/kg DM) reduced the meat tenderness (Wang et al., 2007). Furthermore, retinoic acid enhances collagen synthesis by fibroblasts, accompanied by reduced lipid accumulation, which might explain the increase in shear force of beef from the higher vitamin A intake group (Zasada and Budzisz, 2019).

On the other hand, complete restriction of vitamin A to Angus steers during feedlot for 6 mos increased the number of USDA Choice and Prime carcasses in the finished cattle (Pickworth et al., 2012b). Lower vitamin A supplementation (723 IU/kg DM) for ∼5 mos to Simmental and Angus Steers with depleted liver retinol storage and to Angus steers with (600 IU/kg DM) regular liver retinol level for ∼10 mos increased IMF %, and the number and size of marbling flecks increased by 22% (Knutson et al., 2020; Kruk et al., 2018). Yearling steers typically have sufficient retinol stores for about 3 mos, and exposure to a low-vitamin A basal diet for longer than 3 mos depletes liver retinol stores, reflected in reduced serum retinol levels (Bryant et al., 2010; Wellmann et al., 2020). As hypertrophy becomes prominent during this stage, low retinol levels reduce lipid oxidation, which promotes lipid storage and marbling fat accumulation (Tourniaire et al., 2015). Therefore, vitamin A restriction throughout the entire finishing stage can effectively promote adipocyte hypertrophy and IMF deposition in beef cattle (Figure 3).

Sex-specific effects of vitamin A supplementation on marbling

The sex-specific impact of vitamin A treatment during neonatal stages in terms of marbling is ambiguous from the available studies. All the neonatal vitamin A treatment trials were conducted on Angus cattle, where the IMF content was measured after finishing on steers only (Harris et al., 2018) (Yu et al., 2022) (Maciel et al., 2022). In Hanwoo cattle, both male and female calves were treated with oral vitamin A supplementation and the genes related to preadipocyte development at 2 mos of age; however, the sex-specific comparisons were not carried out (Peng et al., 2020). The only vitamin A trial that evaluated its sex-specific effect on both the prenatal and neonatal stages was conducted on Nellore × Angus crossbred cattle, and the overall difference of IMF content between steers and heifers was not significant, and the stage-specific difference between the two sex groups was not consistent (Ladeira et al., 2024). In brief, available studies indicate that vitamin A treatment enhanced the IMF deposition, particularly in steers; however, the impact on heifers or sex-specific effect is not conclusive due to a lack of comprehensive studies involving both steers and heifers.