Mineral requirements have been studied, given that their precise estimation is essential for optimizing animal nutrition, reducing mineral excretion, and mitigating environmental contamination. The bioavailability of minerals can be modulated by complex interactions within the organism (Lee et al., 2002), which may either enhance or inhibit their absorption and utilization (Underwood and Suttle, 1999). Such interactions can compromise the fulfillment of dietary requirements and contribute to the onset of metabolic disturbances (NRC, 1985).

Microminerals or trace elements are distributed throughout the animal body in small quantities, corresponding to less than 0.3% of the total minerals deposited in the body, but are of great importance for maintaining normal cellular metabolism (Suttle, 2022). Among trace minerals Copper, Mn and Zn are components of enzymes and contribute to increased resistance to infection, play essential physiological roles in ruminants. Zinc is involved in numerous biological processes, including DNA synthesis, gene expression, and cell proliferation. It also plays a pivotal role in bone formation through its structural integration into the enzyme alkaline phosphatase, which is crucial for bone mineralization (Hosnedlová et al., 2007). Iron, in turn, is a fundamental component of the heme group within the protoporphyrin ring of hemoglobin, facilitating the transport of oxygen from the lungs to peripheral tissues as oxyhemoglobin, and the return of carbon dioxide as carboxyhemoglobin via the venous circulation. Furthermore, Fe acts as a cofactor for various enzymes associated with the tricarboxylic acid (Krebs) cycle and participates in oxidative metabolism through its role in catalases and peroxidases (Suttle, 2022). Mn is a required component of manganese superoxide dismutase (MnSOD) for reducing mitochondrial oxidative stress (Li and Yang, 2018). The Iron and manganese minerals prevent the deleterious action of free radicals, being classified as preventive antioxidants.

Deficiencies in these trace minerals may adversely affect growth performance and maintenance of normal cellular metabolism (Zhang et al., 2018), attenuate immune function, and heighten the animal’s vulnerability to infectious and metabolic diseases. In this context, the functional significance of trace minerals in maintaining and promoting animal health has received growing scientific attention (Mortazavi et al., 2025).

Historically, equations to estimate mineral requirements for sheep do not consider the effect of sex (NRC, 2007). However, studies have shown differences between males and females (Vargas et al., 2017; Herbster et al., 2023). These differences may lead to variations in mineral concentrations in tissues and blood between the sexes (AFRC, 1998; Meschy, 2000; NRC, 2007). Knowing the amount of minerals consumed by the animal as well as the amount retained in its body is necessary to determine the need for trace elements for the maintenance and growth of the animals. Adequate mineral nutrition is essential to optimize animal performance because trace minerals play roles in animals such as structural function, constituents of body fluids, acid-base balance, control of osmotic pressure, enzyme cofactors, and the formation of metalloenzymes (McDowell, 2003; Wilson et al., 2016; Suttle, 2022). Additionally, most studies have not considered the effect of sex classes on trace element requirements, which is an imminent need.

Furthermore, when estimating dietary mineral requirements based on each mineral’s absorption coefficient, it assumes minimal urinary mineral excretion. However, not every mineral is absorbed and retained, and has important functions in the body (BR-Corte, 2016). Therefore, determining mineral maintenance requirements by assessing the balance between mineral intake and retention in the animal’s body is more accurate than using the absorption coefficient, as the retention coefficient accurately reflects the proportion of ingested minerals that are effectively retained, providing a more accurate assessment of mineral utilization in sheep.

We hypothesized that the traces elements requirements of hair sheep differ between sex classes. Thus, this study aimed to estimate the net requirements for gain (NCug, NFeg; NMng; NZng, NCog, and NCrg) and maintenance (NCum, NFem; NMnm, NZnm, NCom; and NCrm) in males and female hair sheep.

Following the selection of the optimal combinations between the allometric models and variance functions for each trace element, the corresponding model parameters and variance structures were used to estimate growth mineral requirements, as presented in Table 4. As no significant effect of sex was observed, generalized prediction equations for net concentrations of mineral use for gain (NCug and NCog) were developed.

The combination of the linear model with exponential variance was the best choice for Mn, Zn, Co, and Cu. However, this combination was unanimous (w > 0.90) only for Mn and Cr. For Fe and Cu, the allometric model with homogeneous variance was the best choice among the candidate models (Table 5).

The models for estimating the net requirement for weight gain are presented in Table 6. The net requirements for gain in hair sheep, along with their respective confidence intervals, are summarized in Table 7. Irrespective of sex, the Fe requirements for gain decreased with increasing BW from 10 to 30kg and average daily gain (ADG) of 150 g/day, ranging from 11.54–8.93; 10.58-6.81; 7.16-2.91 mg of Fe for non-castrated males, castrated males, and females, respectively. During growth, non-castrated males showed greater requirements for Mn than castrated males, and females showed greater Mn requirements than castrated males, irrespective of gain. Castrated males had a higher chromium requirement than males and females during growth.

The trace element requirements for maintenance were estimated by relationships between minerals retained and mineral intake. No significant effect of sex was observed on the intercepts or slopes of the linear regression models used to estimate the net requirements of Cu, Fe, Mn, Zn, Co, and Cr (Figure 1). The net requirements for maintenance (µg/kg of body weight) and coefficient retention (%) were as follows:34.85µg/kg of BW and 23% for Cu; 39.63 µg/kg of BW and 13,00% for Fe; 6.11 µg/kg of BW and 0,7% for Mn; 194,00 µg/kg of BW and 28.7% for Zn; 6.06 µg/kg of BW and 13.8% for Co; 11.67 µg/kg of BW and 8.6% for Cr, respectively.

The trace element requirements of non-castrated, castrated males and females from 10 to 35kg BW and an ADG of 150g for Fe were (81.94 mg/day; 68.26 and 38.89 mg/day, respectively); Mn (96.58; 43.97 and 62.24 mg/day, respectively); Zn (34.30; 33.30 and 22.82 mg/day, respectively); Cr (7.85; 8.44 and 4.17 mg/day respectively).

The total dietary requirements of this study, as well as those presented by the NRC (2007) and INRA (2018) Committees, are shown in Figure 2. The estimated dietary requirements for males with a body weight (BW) of 30kg and an average daily gain (ADG) of 150g in the present study were 69.6 mg/day for Fe, 76.06 mg/day for Mn, and 2.62 mg/day for Co. These values exceed the recommendations established by the NRC (2007), which suggest 47.62, 17.4, and 0.17 mg/day for Fe, Mn, and Co, respectively. When compared to the INRA (2018), the current results also indicate elevated requirements for Mn and Co, which were reported as 46.87 and 0.28 mg/day, respectively. The estimated dietary requirements for Cu and Zn in hair sheep males were 6.38 and 38.34 mg/day, respectively, exceeding the values recommended by the NRC (2007), which are 4.65 mg/day for Cu and 19.60 mg/day for Zn. In contrast, the Zn requirement determined in the present study was lower than that proposed by INRA (2018), which recommends 46.87 mg/day for animals with similar physiological characteristics.

A factorial approach has been used to describe trace elements requirements (ARC, 1980). The method entails estimating maintenance, growth, pregnancy, and lactation requirements separately, and subsequently summing them to estimate the total net requirement. The significant advantage of using the factorial method lies in the capability to predict requirements across a diverse range of production circumstances. By dividing the sum of maintenance and production requirements by the absorption coefficient (NRC, 2007) or retention (BR-CORTE, 2016) of the mineral, the dietary requirements can be determined.

In our study, regardless of sex, the sheep exhibited similar requirements for Cu and Co, and the demands increased with increasing body weight. Cu has essential functions in the organism of animals, being necessary for cellular respiration, bone formation, cardiac function, connective tissue development, spinal cord myelination, and keratinization (NASEM, 2016). Based on the present findings, the estimated Cu requirement for maintenance was 0.03485 mg/kg of body weight (BW), with a retention coefficient of 23%. These values are notably higher than those reported by Suttle (2022) and Grace and Clark (1991), who estimated net Cu maintenance requirements at approximately 4 µg/kg BW/day for animals weighing between 20 and 35kg. Cu requirements are peculiar, as they are affected by interactions with Fe, Mo, and S, making it necessary to specify the conditions under which the requirements are applied. Mo in the presence of S markedly reduces the uptake, storage, and utilization of Cu. This occurs through the synthesis of thiomolybdates in the rumen-reticle and formation of insoluble copper in digesta (Suttle and Field, 1983). In our study, sheep weighing 30kg with an ADG of 150g (GPVZ of 136g), the demand corresponds to 1.05 and 63.85 mg Cu/day for the net requirements of maintenance and weight gain. In NRC (2007), using the factorial method, the value of 0.004 mg Cu/kg of BW (4 µg Cu/kg of BW) is adopted, considering the Cu absorption coefficient of 6.0% in lambs, under feedlot conditions. Cu requirements for sheep were first described as 5 mg/kg DM (NRC, 1975) and were later adjusted to 7–11 mg (NRC, 1985). In the ARC (1980), it was suggested that requirements vary from 1 to 8.6 mg of Cu/kg of DM, depending on the physiological state of the animals.

In our study, males and females have similar dietary demands for Co. Co is the precursor of vitamin B12, and is therefore related to energy metabolism, but the amount of dietary Co converted into vitamin B12 varies from 3 to 13% of the Co consumed (Smith, 1987). Studies by Monroe et al. (1952); Looney et al. (1976) with cattle found that 84 to 98% of the Co supplied in the diet was found in the feces, around 5 to 14 days after intake. In this study, the value of 13.8% was estimated as the true retention coefficient, showing that 86.2% of the intake was excreted via feces and urine. Furthermore, the net Co requirements for maintenance in sheep were estimated at 6.06 µg/kg BW. The present study indicates that the net cobalt requirement to support a daily weight gain of 200g in sheep is 2.63 mg/day for an individual with a BW of 30kg. The dietary requirement is relatively higher than the suggestions of INRA (2018), which recommendations of 0.28 mg of Co/day. The NRC (2007) recommends 0.10-0.20 mg Co/kg DM for sheep. CSIRO (2007) suggests a value of 0.11 mg Co/kg DM. According to McDowell (2003), except for P, Co deficiency is one of the most severe mineral deficiencies affecting ruminants in tropical pastures. Co is essential for the synthesis of vitamin B12 by rumen microorganisms (Van Soest, 1994). In the metabolism of ruminants, vitamin B12 is an essential part of multiple enzymes involved in the metabolism of carbohydrates, lipids, some amino acids, and DNA (González-Montaña et al., 2020).

In this study, sex influenced weight gain requirements for Fe, Mn, Zn, and Cr. Around 60% of the Fe in the animal’s body is associated with hemoglobin. The Fe requirement for hair sheep for maintenance is 0.03963 mg of Fe/kg of BW and a retention coefficient of 13%. Sex classes influence the requirements for weight gain, for non-castrated, castrated males, and females weighing 30kg with an ADG of 150g (EBWG of 136). The amount of Fe deposited in the gain and, therefore, the net amount of the mineral required is 8.93, 6.81, and 2.91 mg Fe/day, respectively. The estimates obtained for males by this study are similar to the general recommendation for growing sheep from NRC (2007), of 8.25 mg/day. Fe is one of the most abundant mineral nutrients in the organism and plays a critical role in the synthesis of nucleic acids and proteins, electron transport, cellular respiration, proliferation, and differentiation (Lieu et al., 2001), all of which are intimately related to spermatogenesis and spermatozoa metabolism (Wise et al., 2003).

The net Mn requirement for maintenance was 0.00611 mg/kg of BW and a retention coefficient of 0.7%. For a sheep weighing 30kg BW, the maintenance and dietary Mn requirements are 0.183 and 72.86 mg Mn/day, respectively. In both ARC (1980) and NRC (1985) Systems, values of 10 and 20 mg of Mn/kg of DM are suggested, respectively. Masters et al. (1988) recommended 13 mg Mn/kg DM. The NRC (2007) suggests a requirement for a weight gain of 0.47 mg of Mn/kg BW. Using the prediction equation of this study to estimate the requirement of females with 30kg of BW, with an ADG of 150g (EBWG of 136g), the demand corresponds to 0.28 mg Mn/day, a requirement lower than that of non-castrated males, which require 0.55 mg Mn/day. Males have greater Mn requirements due to testicular growth. Thus, Mn requirements for spermatogenesis and testicular development may be significant. A similar situation occurs with Cu and Mn for females in the reproductive period (Underwood, 1981).

Zinc plays a pivotal role in cellular proliferation, preservation of cellular integrity, and modulation of immune responses, being a key component in the host defense against pathogenic agents (Mortazavi et al., 2025). Since most trace elements, the key role of Zn in animal organism is related to its structural function in some proteins or as an enzyme activator (Suttle, 2022). In this sense, approximately a thousand proteins associated with Zn are recognized in animal organisms. Zinc, an essential component of life in the three domains, follows iron as the second most abundant transition metal ion in living organisms (Cuajungco et al., 2021). Based on the findings of the present study, a net maintenance requirement of 0.194 mg of Zn/kg of body weight (BW) and a retention coefficient of 28% are proposed for sheep, regardless of sex class.

Comparatively, the ARC (1980) established Zn requirements for growing sheep ranging from 24 to 51 mg/kg of dry matter (DM), while the NRC (1985) adopted a value of 20 mg/kg DM. More recently, the NRC (2007) recommended a net maintenance requirement of 0.076 mg Zn/kg BW, with an estimated absorption efficiency of 30% for lambs. This study suggests that non-castrated, castrated males, and females weighing 30kg with an ADG of 150g (EBWG of 136g) demand 5.37, 5.0, and 1.57 mg Zn/day, respectively. Zinc is a component of many metalloenzymes involved in almost every metabolic pathway of the body (Salgueiro et al., 2000). Zinc deficiency alters prostaglandin synthesis, which may affect luteal function (Graham, 1991).

Discussions occur about whether or not chromium is considered an essential element, however, NRC (2007) and NASEM (2016) consider this element as essential. Our study makes an interesting contribution to the requirements for chromium, as it is considered an element, suggesting that the net requirement for maintenance is 0.011 mg Cr/kg BW, and the retention coefficient is 8.6%. For a 30kg sheep, the value of 0.35 mg/day is suggested as a net requirement for maintenance. For dietary requirements, 9.47, 10.31, and 4.88 mg of Cr/day are recommended for non-castrated, castrated, and females, respectively. Although studies on chromium essentiality in sheep are scarce, NRC (2007) states that neither deficiency nor toxicity will likely occur under normal conditions. Therefore, there are no reports of signs of mineral deficiency in animals and humans. However, considering Cr’s relationship with the immune system and its anti-stress effect, some studies have shown reduced morbidity, mortality and increased efficiency in animals recently transported over long distances, both calves and steers that received supplementation with Cr, especially in the organic form (Moonsie-Shageer and Mowat, 1993; Mowat et al., 1993). Likewise, Cr improves the resistance of cattle to diseases, due to its role in stimulating the immune response (Wright et al., 1994). According to the equations suggested in our study for non-castrated, castrated males, and females weighing 30kg with an ADG of 150g (EBWG of 136g), the net amount of the mineral required is 0.46, 0.54 and 0.07 mg of Cr/day, respectively. The net Cr requirement for growing sheep is greater for castrated sheep.

Based on the present study, the trace element requirements for hair sheep were different from those reported by the World Committees. Both the NRC (2007) and INRA (2018) recommendations for trace mineral requirements are based primarily on estimates established by the ARC (1980). In these Committees, trace element requirements were determined using the dose-response methodology and absorption coefficients. In dose-response, the animal’s requirement for a nutrient is given at the maximum response level in the parameters evaluated, such as maximum weight gain, for example. This method may lead to underestimation or overestimation of the estimates, since it is not possible to vary the production levels, since the estimate is based on the maximum response to the productive demand. Furthermore, most studies did not consider the trace elements contained in the feeds that made up the experimental diets.

Another approach that should be considered is the differences between organic and inorganic nutrients in terms of their requirements for maintenance and production result in different metabolic pathways. Organic nutrients, such as protein, for example, after being absorbed, enter the body’s metabolic pool and can be converted to energy, used for tissue synthesis or maintenance; they can be metabolized and deposited; or they can be lost, as end products of metabolism, through normal pathways. In contrast, inorganic ions released during metabolism are not altered, nor do they become unavailable to the tissues. These ions remain available for reformulation of their functional combinations, in the same way as inorganic ions absorbed by the digestive system (Underwood, 1981). This reuse of minerals by the tissues could theoretically be complete, resulting in the absence of maintenance requirements for these nutrients. However, in practice, the mineral conservation processes in the body are not as efficient, resulting in loss of minerals through the kidneys, intestinal mucosa, digestive glands, and skin, thus constituting the mineral requirements for maintenance. The recommendations of various Committees take into account their calculations of endogenous losses through feces. The mineral maintenance requirements encompass not only urinary and fecal losses, but also potential losses through the skin, sweat, and other routes. Regarding the mineral retention coefficients, the values observed for manganese and chromium were relatively lower, which may be attributed to the high concentrations of these minerals in the diet, thereby resulting in increased excretion. can be attributed to endogenous losses associated with variations in voluntary intake, which directly influence maintenance needs. Therefore, the use of the true retention coefficient seems to be more accurate compared to the absorption coefficient for estimating mineral requirements. Thus, while the estimates have been refined, the retention coefficients identified in this study are not definitive and may fluctuate in response to tissue growth. Younger animals typically exhibit higher retention coefficients compared to adults. Therefore, the extent of variation in retention and absorption coefficients concerning growth stages remains to be further elucidated.

Minerals play an important role in animal metabolism, and study contributes to improving our knowledge about recommendations for mineral requirements in hair sheep. However, there exists a need for additional efforts to better understand the effects of genotype and degree of maturity on trace elements requirements, especially requirements for maintenance and growth. Herein, there is a great contribution in providing up-to-date recommendations on trace elements requirements for sexes. Furthermore, the importance of future studies to determine trace elements requirements is highlighted. Finally, there is a need for more in-depth knowledge of the retention coefficients of different minerals. Continuous efforts to improve models for estimating trace elements requirements, together with a better understanding of retention coefficients, will provide greater reliability in the formulation of diets for sheep raised in tropical regions.

In conclusion, our study makes a significant contribution by demonstrating the influence of sex on the trace mineral requirements of hair sheep. The requirements for Mn, Co, and Cr increased with increasing body weights, whereas Fe and Zn showed a stable tendency. Our study indicated that the hair sheep trace elements requirements are different from the main nutritional requirements established by NRC (2007) and INRA (2018). Accurate estimation of the mineral requirements of growing sheep necessitates precise knowledge of mineral deposition in the body. It is important to emphasize that trace elements requirements serve as guidelines for the animal’s needs and should be reassessed as new information becomes available. Estimating the various requirements through multiple approaches is advisable. Achieving reasonable agreement between methods means greater confidence in the estimated trace mineral requirements.