**1. Introduction**

Climate change has been feared to incur frequent drought spells and floods, while temperature fluctuations and shifting of rainfall patterns are projected to alter growth habits of weeds flora globally. There is an emerging rhetoric that most of invasive and indigenous weeds have the potential and botanical superiority to adjust and acclimatize to atmospheric CO2 enrichment through the optimization of photosynthesis process leading to significant boost in their biomass production. In this way, some of the weed species can increase their establishment and dominance in indigenous agro-ecosystems along with invading adjacent as well as far flung terrestrial ecosystems. Thus contrary to notion that weeds are menace and agro-ecological systems must be kept free of indigenous and invasive weeds, their utilization as forage for dairy animals has the potential to become the most feasible and pro-environment strategy [1–3].

Globally, large ruminant's performance is directly influenced by the nutritional value of feed which accounts for over 50% of total expenditures. It deserves mentioning that dairy animals confront forage shortage owing to temperature extremes leading to drastic fall in milk production especially in developing countries. The shortage of forage and rising population of dairy animals has necessitated identifying and evaluating alternate feed resources which are cheap and can also fulfill animal's dietary needs. It has been established that weeds can inflict drastic influence on crops productivity and use of chemical herbicides for keeping them below threshold level, has led to serious concerns pertaining to their residual persistence in crops, soil and environment. Weeds utilization as animal feed holds potential because these are cheap owing to their abundance on field paths and water channels. Weeds harvested from cropped and non-cropped area may constitute an effective and biologically viable approach to keep weeds below the threshold level. Weeds utilization for feeding animals can also reduce herbicides use in agricultural lands which has the potential to curb environmental pollution. Many weeds have been reported to be resistant and better adapt to dynamic environmental conditions, and thus making them less prone to drastic impacts of climate change. In addition, it was reported that animals preferred naturally grown mixtures of weeds over crop residues and roughage during dry season. Furthermore, rapid regeneration favors many weed species for their inclusion as a source of vegetable protein in animal's diet [4–10].

Weeds such as Bermuda grass (*Cynodon dactylon*), Johnson grass (*Sorghum halepense*), canary grass (*Phalaris minor*), nut sedge (*Cyperus rotundus*), cheat-grass or drooping brome (*Bromus tectorum*), burr clover (*Medicago polymorpha*) and pigweed (*Amaranthus viridis*) contained organic matter over 90% indicating that these weeds can fulfill the dry matter requirement of animals. In addition, spotted knapweed (*Centaurea stoebe ssp. micranthos*), a weed of rangelands in Northern America was reported to displace local plant species, degraded wildlife habitats, altered biogeochemistry of soil and triggered soil erosion and thus its control through grazing was found to be biologically and economically viable. Similarly, broom snakeweed and medusa-head (*Taeniatherum caput-medusae*) were effectively controlled through controlled grazing with reasonably good palatability [11–17].

Along with substantial quantity, nutritional quality of weeds is of the utmost importance for dairy animals in order to produce milk on sustainable basis. Field bindweed (*Convolvulus arvensis*) and yellow duck (*Rumex crispus*) were reported to have significantly higher protein content (27 and 22% respectively) [11] which were greater than all cereal forages and most of the legumes, while button weed (*Diodia scandens*) contained 7.7% protein [18]. Although, a number of species belonging to *Commelinaceae* family such as climbing dayflower (*Commelina diffusa* L.), tropical spiderwort/wandering jew (*Commelina benghalensis* L.), Asiatic dayflower (*Commelina communis* L.), African dayflower (*Commelina africana* L.), white mouth dayflower/slender dayflower (*Commelina erecta*) are considered weed but constituted a major chunk of animal feed in Tanzania [19], rural regions of Mauritius [20], USA [21] and in Kenya owing to reasonably good palatability [14, 18, 22, 23].

It is pertinent to mention that anti-nutritional factors (saponins, tannins, oxalates, etc.) of weeds constitute as the most crucial concern as far as animal nutrition is concerned. Tick weed (*Cleomea viscose*) recorded safer limits of anti-nutritional factors such as condensed tannins (0.0491%), saponins (0.23%), phytates (1.2%)

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selection criteria.

*Changing Climate and Advances on Weeds Utilization as Forage: Provisions, Nutritional Quality…*

and oxalates (3.3%), but unfortunately in-depth studies are lacking in this context. Furthermore, narrow leaf weeds (nut sedge, wild oat, etc.) were recommended to be a good source of fiber, while broad leaf weeds (pigweed, field bindweed, etc.)

To date, very few studies have been done to assess the nutritional status, digestibility and intake of indigenous and exotic (invasive) weeds and their utilization in sustainable ruminant's production systems, but not a single study has so far synthesized and evaluated the literature on weeds utilization as forage. This chapter attempts to synthesize as well as assess the potential of weeds for supplementing traditional feedstuffs (forages, crop residues and concentrates) partially without compromising the productivity of large ruminants in terms of milk production. Weeds mineral constituents and anti-nutritional factors and various implications in

In order to synthesize published findings pertaining to nutritional quality of weeds, search was performed on Google Scholar (http://scholar.google.com) and PubMed (http://www.PubMed.gov) using the below mentioned search strings:

The search was time-restricted to 2000–2019, however owing to limitation of

1.Reporting at least one weed's biomass production under changing climate.

2.Describing one or more nutritional quality parameters such as protein content

The screening process resulted in 55 studies which fully fit in the objectives and

The rising temperature and carbon dioxide level along with the rapidly altering dynamics of rainfall and evaporation are the most important factors for determining management and utilization of weeds under changing climate. Weeds have been reported to have a greater genetic diversity compared to crops and thus can respond positively to agro-environmental changes. Owing to CO2 enrichment of atmosphere and rising temperature, some of the weed species can invade new

provided cheap vegetable protein to dairy animals [1, 11, 13, 20].

weeds utilization as animal feed have also been evaluated.

*DOI: http://dx.doi.org/10.5772/intechopen.91386*

**2. Materials and methods**

1.Weeds and forages.

3.Weeds, animal feed.

2.Weeds nutritional value.

4.Anti-nutritional factors in weeds.

of indigenous or invasive weeds.

**3. Weeds under changing climate**

published findings; it was later on relaxed to 1990–2019.

3.Stating anti-nutritional factors of weeds species.

The research studies were screened based on following criteria;

4.Reporting mineral constituents of at least one or more weeds.

*Changing Climate and Advances on Weeds Utilization as Forage: Provisions, Nutritional Quality… DOI: http://dx.doi.org/10.5772/intechopen.91386*

and oxalates (3.3%), but unfortunately in-depth studies are lacking in this context. Furthermore, narrow leaf weeds (nut sedge, wild oat, etc.) were recommended to be a good source of fiber, while broad leaf weeds (pigweed, field bindweed, etc.) provided cheap vegetable protein to dairy animals [1, 11, 13, 20].

To date, very few studies have been done to assess the nutritional status, digestibility and intake of indigenous and exotic (invasive) weeds and their utilization in sustainable ruminant's production systems, but not a single study has so far synthesized and evaluated the literature on weeds utilization as forage. This chapter attempts to synthesize as well as assess the potential of weeds for supplementing traditional feedstuffs (forages, crop residues and concentrates) partially without compromising the productivity of large ruminants in terms of milk production. Weeds mineral constituents and anti-nutritional factors and various implications in weeds utilization as animal feed have also been evaluated.
