Livestock is crucial in India’s agricultural landscape, significantly contributing to millions of farmers’ rural economy and livelihoods. According to the 20
th Livestock Census, the total Livestock population is 535.78 million in the country showing an increase of 4.6% over the Livestock Census 2012. The total number of cattle in the country was 192.49 million in 2019, a rise of 0.8 % over the previous Census (
Statistics, 2019). India is the largest milk producer in the world, the livestock sector accounts for about 4.11% of the national GDP and 25.6% of the agricultural GDP, underscoring its economic importance. Dairy farming is particularly prominent with India being the largest milk producer in the world, producing around 188 million tonnes annually. This sector not only provides nutritional security but also generates substantial employment, particularly for women and smallholder farmers. In addition to dairy, the country is a significant producer of meat, eggs and wool, catering to both domestic consumption and export markets.
Fodders are essential to livestock nutrition, providing a balanced diet that supports overall animal health, growth and productivity. They are primary sources of energy, with grasses and cereals supplying carbohydrates needed for maintenance and production activities. Leguminous fodders like alfalfa and clover are rich in protein and crucial for muscle development, milk production, and growth. Additionally, green fodders offer vital vitamins (A, D, E, K) and minerals such as calcium and phosphorus, which are necessary for various metabolic functions. The high fibre content in fodders aids in proper digestion and prevents digestive disorders. Different types of fodders, including green fodder, silage, hay and crop residues, provide versatility in feed, ensuring year-round availability and nutritional adequacy
(Kumar et al., 2016). Green fodder is highly palatable and nutrient-rich, while silage and hay, preserved through fermentation and drying respectively, are critical during off-seasons. Crop residues like straw are efficiently utilized, reducing waste and promoting sustainability. Proper nutrition from fodder enhances growth rate, reproductive health, milk yield and disease resistance, contributing to the overall productivity and profitability of livestock farming
(Bouis et al., 2011). Cultivation and utilization of fodder are cost-effective, reducing dependence on expensive commercial feeds and promoting local agriculture
(Karthikeyan et al., 2024). Sustainable practices in fodder production improve soil health through crop rotations and nitrogen fixation by legumes, enhancing farm biodiversity and resilience to climate variability. Efficient fodder management, including quality control and preservation techniques, ensures a continuous supply of high-quality feed, essential for animal welfare and optimal production
(Ravi et al., 2024). Encouraging farmers to utilize locally grown fodders can help them minimize their carbon footprint and cultivate sustainable farming communities, thereby bolstering the economic viability and environmental sustainability of livestock farming.
Despite being the world’s largest milk producer, the animal productivity of India (1538 kg/year) is lower than the global average (2238 kg/year), which may be related to malnutrition because of the massive feed shortage. The country is experiencing a net deficit of 30.65% of green fodder, 24.6% of crude protein and 19.87% of total digestible nutrients (
Statistics, 2019). The excessive application of chemical fertilizers devoid of micronutrients to meet the increased demand for forage has negatively impacted soil health and decreased crop yield
(Ravi et al., 2023). As population pressure rises, more land is allocated to food and cash crop cultivation, leaving limited arable land for fodder production. This highlights the importance of focusing on fodder production in modern agriculture. To meet the high demand for fodder, excessive and continuous application of large quantities of high-analysis chemical fertilizers has had detrimental effects, resulting in decreased productivity due to nutrient limitations. Consequently, it faces major difficulties in optimizing the use of available land to produce adequate and high-quality animal feed. Hence, to address the critical gap in crude protein and total digestible nutrients (TDN) availability in India as given below (Fig 1), it is essential to prioritize the biofortification of fodder crops. Enhancing the nutritional quality of these crops through biofortification can significantly improve livestock productivity and contribute to the sustainability of the agricultural sector. This approach is crucial for meeting the growing nutritional demands of livestock and ensuring food security. Thus, the main objective of this review is to explore the different methods used for biofortifying fodder crops in agronomical approaches. The expected scenario for the availability of total digestible nutrients (TDN) and crude protein (CP) as well as their potential deficiencies are given in Fig 1.
Importance of livestock nutrition
The health and productivity of farm animals, which underpin the world’s food supply are deeply reliant on proper livestock nutrition
(Liu et al., 2021). Adequate nourishment ensures that animals receive the essential nutrients needed for critical physiological functions, growth, reproduction, and lactation. Balanced and species-specific diets, tailored to the varying developmental stages of livestock, further enhance reproductive outcomes, leading to higher birth rates and healthier offspring
(Ajaykumar et al., 2024). Conversely, poor nutrition can result in stunted growth, reduced productivity, and increased vulnerability to diseases, all of which can lead to substantial financial losses (Table 1). Moreover, the quality of animal products, such as meat and dairy, is directly influenced by the diet of the livestock for instance, specific nutrients can affect milk composition and meat marbling.
A significant challenge in livestock management is addressing nutritional imbalances, particularly in dairy goats and cattle. These imbalances, often resulting from inadequate or unbalanced diets, can lead to a range of metabolic and physiological disorders (
Simoes and Gutierrez, 2017). For example, deficiencies in vitamins and minerals among grazing sheep can increase their susceptibility to oxidative stress, metabolic disorders, and other health issues (
Masters, 2018). The cumulative effects of these nutritional deficiencies can have serious repercussions for both animal and human health. Implementing a well-balanced diet and nutrition plan, designed to avoid nutrient toxicities, is crucial for preventing and managing these diseases (
Awuchi, 2020).
Fodder and forage alternatives play a crucial role in cattle nutrition, providing essential nutrients needed for growth, reproduction and overall health
(Saikanth et al., 2023). Nutrient deficiencies in fodder can significantly impact its growth and development, leading to reduced yield and quality
(Bhaumik et al., 2024). This, in turn, directly affects the productivity and well-being of cattle, as well as the nutritional value of the animal products consumed by humans
(Reddy et al., 2023). Addressing nutrient deficiencies in fodder through appropriate management practices and agronomic interventions is vital for ensuring the efficiency and health of both livestock and people. Additionally, micronutrient deficits in agricultural soils can diminish the nutritional quality of crops, potentially contributing to malnutrition in humans
(Bouis et al., 2011).
Biofortification of fodder crops
Biofortification involves enhancing the content and/or bioavailability of essential nutrients in crops during their growth phase by utilizing genetic and agronomic methods
(Bouis et al., 2011). Agronomic biofortification in fodder crops is crucial as it enhances nutrient content through sustainable farming practices, improving livestock nutrition without the need for genetic modification. This method can be quickly implemented and adapted to various environmental conditions, making it a cost-effective and accessible solution. Additionally, it promotes soil health and reduces the reliance on chemical fertilizers, contributing to overall agricultural sustainability
(Jadhav et al., 2020).
Techniques of Agronomic bio fortification
Agronomic biofortification, a key component of biofortification, involves enhancing the nutrient content of crops through soil and foliar application of fertilizers, soil inoculation with beneficial microorganisms and other techniques.
Fertilization in fodder crop biofortification
One of the most significant factors that directly affect the quantity and quality of fodder is the application of fertilizer. The response of dry matter production in maize to the fertilizer rate was linear
(Kumar et al., 2016).
Nitrogen
Nitrogen is a critical nutrient that significantly enhances both crop improvement and fodder crop production. Nitrogen is essential for the formation of several structural elements, including molecules, proteins, amino acids, chlorophyll and other components.
Nitrogen fertilization is essential for improving the quality of forage, especially in terms of dry matter production and the concentration of crude protein
(Maheswari et al., 2017). However, the impact of nitrogen on forage quality can vary depending on the specific crop and the presence of other nutrients such as phosphorus (
Aydin and Uzun, 2005). For example, in cluster bean varieties, nitrogen application significantly increased forage yield and quality, with the variety BR-99 showing the highest yield and protein content. Likewise, applying nitrogen fertilizer to native pasture overseeded with ryegrass enhanced forage qualities and the performance of beef calves
(Brambilla et al., 2012). These results emphasize the significance of nitrogen fertilization in improving forage quality, while also highlighting the importance of a balanced approach that considers the particular crop and the presence of other essential nutrients.
Soil application
When 25 t/ha FYM was applied, the number of micronutrients such as zinc, copper, manganese, and iron in fodder maize was improved by 15.3%, 7.5%, 28.4%, and 15.6% respectively relative to the control, but declined when the amount of nitrogen increased. They have also reported that the application of FYM 25t/ha and nitrogen120kg/ha results in increased crude protein yield (kg/ha) by 33.78 % and 36.56 % respectively (
Knez and Graham, 2012).
Vennila et al., (2017) stated that the application of both organic and inorganic sources of nutrients to bajra Napier hybrid grass increases yield, yield attributes, and nutrient uptake. It was found that the application of nitrogen at the rate of 180 kg/ha results in maximum crude protein contents (10.52%) which might be due to enhanced production of amino acid resulting from nitrogen application and the highest percentage of crude protein (11.54%) and lowest percentage (7.84%) were observed at 45 and 65 days after sowing, respectively
(Swathi et al., 2015).
Livestock nutritional response
Nitrogen enhancement in forage for livestock has been shown to have a positive impact on forage production and livestock performance.
Brambilla et al., (2012) found that nitrogen fertilization increased forage accumulation rate and production, leading to improved livestock performance.
Delevatti et al., (2019) similarly reported that increasing nitrogen levels in Marandu grass improved herbage mass forage quality and animal production. However,
Jacobs and Ward, (2011) noted that the effect of nitrogen application on forage crops was limited by available moisture, with variable dry matter yield responses.
Rouquette and Smith, (2010) highlighted the role of biological nitrogen fixation in reducing input costs for forage production, particularly in cow-calf and stocker programs.
Zinc
Zinc plays a crucial role in the growth and development of fodder crops, particularly maize and cowpea, by improving their yield and quality
(Rathore et al., 2015). Furthermore, it has been noted that zinc is essential for various vital processes in plants, such as protein synthesis and gene expression (
Ahmad and Tahir, 2019). Therefore, the inclusion of zinc in the fertilization and management of fodder crops is crucial for their optimal growth and nutritional value.
Importance of dietary zinc in livestock
The insufficient presence of zinc in forage can lead to substantial effects on livestock, including decreased growth and reproduction, as well as impaired health of bone and skin tissues. The easiest and latest practice to deal with micronutrient deficiency in crops is the application of micronutrient fertilizers
(Gupta et al., 2008). Enhancing the micronutrient content of fodder crops through foliar application is a promising and economical method of agronomic biofortification, which will improve animal health and productivity
Singh Dhaliwal et al., (2023). The agro-qualitative characteristics of fodder are affected by the micronutrient content thereby directly impacting animal productivity. Therefore, fortifying plants with zinc and copper presents a superior approach to addressing their deficiency in both green and dry fodder
(Kumar et al., 2016).
Soil application
The effect of varying doses of zinc fertilizer on plant growth is different among the crops because the response of fodder crops depends on the application of zinc fertilizers
(Mohan et al., 2015). Applying 20 kg/ha of ZnSO
4 heptahydrate as a basal dose result in 31.3% higher zinc content and 50.9% greater zinc uptake compared to the control, along with the highest levels of crude protein, ether extract and ash content in fodder
(Kumar et al., 2017). Application of zinc at a rate of 10 kg/ha to fodder maize significantly improved plant height, leaf area index and green fodder yield (Table 2-3). Additionally, it increased the content and uptake of nitrogen and zinc, while calcium and crude protein content remained unchanged
(Sheraz et al., 2001). Higher crude protein yield which is due to the combined effect of more crude protein content in plants, dry-matter yield, and leafless plants and higher digestible dry-matter yield because of higher digestibility% and higher dry-matter yield was recorded in fodder sorghum with the application of 5 kg Zn/ha
(Verma et al., 2005).
Agronomic management of anti-nutritional factors
Anti-nutritional factors are substances that, either on their own or through their metabolic by products, hinder feed utilization, negatively impacting animal health and production. These factors reduce nutrient intake, digestion, absorption and utilization, potentially causing other adverse effects
(Kumar et al., 2017).
Antinutritional factors in forages
Nitrate toxicity
Nitrate toxicity in livestock can have severe consequences on their health and productivity. Even though nitrate by itself is not harmful to animals, rumen microorganisms in ruminants convert nitrate to nitrite, which they then use as a source of nitrogen by turning it into ammonia (
Lee and Beauchemin, 2014).
The excess uptake of nitrate by plants beyond the limit leads to the accumulation of nitrate at toxic concentrations. Plant density/seed rate, genotypes (variety) and nitrogen management are the agronomic practices that influence nitrate toxicity (
Oberoi and Kaur, 2019). When nitrogen fertilizers are used on sorghum and oats, the unabsorbed nitrates remaining on the plant surface become a substantial source of nitrates in the diet of animals
(Kamra et al., 2015).
Brassica rapa has the lowest nitrate concentration, while
Sorghum bicolor, Avena sativa and
Brassica campestris had the highest. Compared to stem parts, young plants, and plant samples taken in the morning, the concentrations of nitrate were lower in the afternoon in the leaves and mature crops
(Rashid et al., 2019). The highest concentration of nitrate is found in stalks, with leaves and grain following in descending order. The nitrate content of sorghum Sudan grass, piper sudan grass and pearl millet is three times higher in the lower six inches of their stems than in the upper part of the plant
(Kumar et al., 2018).
The effect of irrigation and nitrogen on bajra proved that the nitrate level was significantly lower in irrigated conditions and at an application of 100kg N/ha when compared to the toxicity level (Table 4). However, the amount of nitrate in the unirrigated condition was more than in the irrigated condition and in both cases rise in nitrate as nitrogen levels increased
(Rashid et al., 2019).
Mechanism of Nitrate toxicity in animals
When forages have an unusually high concentration of nitrate, the animal cannot complete the conversion and nitrite accumulates. As nitrite accumulates and enters the bloodstream, it combines with a ferrous ion (Fe
+2) of haemoglobin (Hb) to create methemoglobin (met-Hb) which is incapable of carrying oxygen
(Sidhu et al., 2011). As a result, the blood turns a chocolate brown colour instead of the typical bright red. An animal succumbing to nitrate (nitrite) poisoning actually dies from asphyxiation or a lack of oxygen
(Kumar et al., 2018).
Oxalate toxicity
Frequent ingestion of an excessive amount of oxalic acid can lead to serious intestinal lining irritation and nutritional deficits in animals (
Oberoi and Kaur, 2019). A few nutrients such as N, K, Na and Ca have a role in the buildup of oxalate in forage. Oxalic acid forms strong bonds with various minerals, including calcium, magnesium, sodium and potassium. This chemical interaction leads to the creation of oxalate salts
(Kumar et al., 2018). When dietary calcium (Ca) and ingested oxalate combined insoluble Ca oxalate is formed. This causes abnormalities in the metabolism of calcium (Ca) and phosphorus (P), which results in an excessive mobilization of bone material in animals (
Rahman and Kawamura, 2011).
Oxalate toxicity in fodder crops can vary significantly depending on factors such as plant species, nitrogen fertilization and harvesting interval. Napiergrass experiments revealed a strong correlation between the K concentration and the soluble oxalate level
(Rahman et al., 2008).
Prussic acid toxicity
Prussic acid is typically absent in plants, but certain conditions can cause several common plants to accumulate large amounts of cyanogenic glycosides, which can then convert to prussic acid. The risk of prussic acid poisoning in livestock increases during drought periods and becomes even higher when drought conditions end and stressed, stunted plants start growing again (
Robson, 2007). Ruminant animals, such as cattle and sheep are more prone to prussic acid poisoning compared to monogastric animals like horses and pigs. This is because the lower pH in the stomachs of monogastric animals helps to break down the enzymes that convert cyanogenic glycosides into prussic acid
(Kumar et al., 2018).
Certain conditions can lead to dangerous levels of cyanogenic glycosides in plants. These conditions include periods of rapid regrowth following stunting, such as after a drought breaks, when a crop is eaten back and then allowed to regrow, or when a crop is harvested for hay and then regrows, with levels being highest in young plants with green, growing shoots. Additionally, frosted or wilted plants, herbicide-treated plants, high nitrogen and low phosphorus levels in the soil and specific plant species like sorghum, which can contain more prussic acid than sudan grass, contribute to increased glycoside levels. Varieties within these species can vary in their prussic acid potential. Plants that are wet with dew or light rain also exhibit higher glycoside levels (
Robson, 2007).
