Maize cobs are rich in fibre and poor in protein, and are thus a low-quality roughage. Despite this low value, their wide availability, large quantities, easy and cheap procurement, and also their large cellulose and hemicellulose reserves enhance their utilization as energy sources in ruminant feed, particularly in areas or during times where better ingredients are not available (Adebowale, 1992). In Nigeria, for instance, maize cobs are an important crop residue used by livestock farmers during the dry season, at a period when they are relatively available and abundant (Ogunleke et al., 2014). In Thailand, maize cobs have been described as the most prominent crop by-product (Wachirapakorn et al., 2014). However, the high lignocellulosic content of the residues requires supplementation, processing, or both. For efficient utilization, supplementation with green forage or browse plants, or readily available source of carbohydrates and nitrogen such as cassava tops or peels, is essential for satisfactory production. Numerous experiments have also demonstrated the benefits of treating maize cobs with alkali (especially NaOH and urea), but such chemicals may be too expensive to buy in developing countries and/or too dangerous to handle in smallholder farming situations (Adebowale, 1992).
Maize cobs are not very palatable to ruminants (Göhl, 1982). Adding 1% molasses may help to improve intake (Ndlovu et al., 1985).
Digestibility and degradability
Reported OM digestibility values vary greatly, from 15-29% to more than 50% (Kategile et al., 1979; INRA, 2007). In vitro DM digestibility at maturity was reported to be in the 50-56% range (Masoero et al., 2006). Like other fibrous materials, treating maize cobs with alkali improves their nutritional value. The in vivo DM digestibility of maize cobs increased from 54 to 62% when they were treated with 4% NaOH, and to 66% when they were treated with Na2O2 (Klopfenstein et al., 1972). In Tanzania, a series of experiments with lambs confirmed that NaOH treatment improved DM and OM digestibility by 5-10 percentage points, though lower OM digestibility values were reported (15-29% for untreated cobs and 30-47% for treated cobs) (Kategile et al., 1979). Urea treatment (6.5%) increased the effective degradability of the DM and NDF of maize cobs from 23 to 32% and from 25 to 31%, respectively (Ramirez et al., 2007). Supplementation with alfalfa hay (30% of the total feed) of a maize cobs-based diet fed to mature sheep increased the rates of evacuation of indigestible material from the rumen (Ndlovu et al., 1985). Grinding may improve the digestion rate of maize cobs and feed efficiency (Ndlovu et al., 1985; Murali et al., 1989), and many experiments are based on ground maize cobs.
Maize cobs in supplemented diets
Supplementation of maize cobs with sources of energy and nitrogen, involving methods that are realistic of small farm situations, is often a cheaper and simpler way of feeding them than chemical treatment (Adebowale, 1992). Grinding and/or pelleting are recommended.
Maize cobs have contributed to diets for dairy cows for many years in the USA. When fed with restricted grain rations, ground maize cobs have replaced up to 60% of the roughage (alfalfa hay or alfalfa-brome hay) without affecting milk production or composition, although feed intake was reduced when maize cobs were the only source of roughage (Lassiter et al., 1958). Ground maize cobs replacing 50% of alfalfa-grass hay resulted in a lower milk yield but in higher weight gain (Graf et al., 1953). Ground maize cobs included at 20% of the ration were a better roughage than ground alfalfa hay, and equal to chopped alfalfa hay, for maintaining feed intake and milk production, but neither cobs nor alfalfa hay maintained the pretrial milk fat concentrations (Emery et al., 1964). In Thailand, feeding a diet containing 14% protein with maize cobs as a roughage source (20% in the total mixed ration) was adequate for supporting crossbred Holstein Friesian lactating dairy cows producing 11-13 kg milk/d (Wachirapakorn et al., 2014).
In the USA, ground maize cobs could be used successfully in place of either dehydrated alfalfa or soybean flakes, as the major roughage in balanced high-roughage pelleted diets for dairy calves (up to 57% cobs in some diets) (Hibbs et al., 1978). In India, maize cobs were incorporated at 50% of the diet as the sole source of roughage in complete feeds of crossbred bulls. There were no deleterious effects, and grinding the cobs through 8-mm sieve was considered optimum (Murali et al., 1989). In Nigeria, 20 White Fulani steers were fed ad libitum on treated and untreated maize cobs with fresh Siam weed (Chromolaena odorata) (2 kg/head/day). Live-weight gain improved from a loss of 0.32 kg/d, when animals were fed untreated maize cobs, to a gain of about 0.48 kg/d, when cobs were treated and supplemented with Siam weed. Animals on untreated maize cobs were taken off the experiment within 3 weeks because of weight loss (Adebowale, 1992).
In Nigeria, maize cobs supplemented with forage legume improved sheep performance, the highest feed intakes, weight gains and digestibilities of DM, protein and fibre being observed with added Leucaena leucocephala and Gliricidia sepium forage (Fasae et al., 2014). In West African Dwarf sheep, a diet based on 75% maize cobs and 23% brewers grain resulted in lower growth and feed use efficiency than a diet containing 50% cowpea husks (Vigna unguiculata), 25% maize cobs and 23% brewers grain (Ososanya et al., 2013). In India, ground maize cobs (8-mm sieve) were fed ad libitum, either as a mash or pelleted, as the roughage for adult sheep (with 250 g/d of concentrate mixture) without any deleterious effect, but pelleting improved nutrient utilization (Reddy et al., 1991). In lambs, ground maize cobs completely replaced finger millet straw (Eleusine coracana) in diets made of 50:50 roughage:concentrate (Senani et al., 2013).
In Nigeria, inclusion of up to 30% maize cobs in the diets of West African Dwarf goats (supplemented with brewers grains, wheat offal and palm kernel cake) gave the best growth performance. There were no deleterious effects on the haematological and serum biochemical parameters and, therefore, they were considered safe to include in ruminant diets up to 30% (Ogunleke et al., 2014). In India, adult goats were maintained on a diet of 60% maize cobs and 40% commercial mixture (Rajmane et al., 2000). Ground maize cobs (8-mm sieve) were fed ad libitum, either in a mash or pelleted, as roughage for adult goats (with 250 g/d of concentrate mixture) without any deleterious effect, but pelleting improved nutrient utilization (Reddy et al., 1991).
Chemically treated maize cobs
Numerous trials conducted in the USA in the 1970s showed that ensiled maize cobs treated with NaOH, KCl or Ca(OH)2 (or combinations of these treatments) gave similar or even better performance in steers and lambs than maize silage, even when maize cobs were included at 70-80% of the diet, provided that the diet was adequately supplemented (see review by Demarquilly et al., 1976).
In crossbred dairy cows in Pakistan, ensiling maize cobs treated with 5% urea, with an additive of 6% maize dextrose, improved N retention and dairy performance compared to urea-treated cobs ensiled without dextrose (Khan et al., 2004).
In the USA, steers fed 80% ensiled maize cobs treated with 3% KCl had a daily gain almost twice that of steers fed maize silage (0.73 vs. 0.30 kg/d) (Koers et al., 1970).
Ground maize cobs fed to swamp buffaloes with urea at 15 g/kg were efficiently utilised in the rumen, and thus provided good fermentation end-products and an improved rumen ecology (Wanapat et al., 2009).
In the USA, lambs fed ensiled maize cobs treated with 4% NaOH had average daily gains similar to those obtained with maize silage (Koers et al., 1972). In rations for growing lambs, treating and ensiling ground maize cobs with 3% NaOH plus 1% Ca(OH)2 increased average daily gain, feed intake and feed efficiency over cobs treated with 4% NaOH (0.15 kg/d vs. 0.12 kg/d), possibly because of the lower concentration of Na (Rounds et al., 1976). In Egypt, feeding rams ad libitum with maize cobs treated with 1% urea (supplemented with 500 g/d of a commercial mixture) had beneficial effects on body weight, daily gain and reproductive performance (testosterone production, semen quality, ram fertility) (Megahed et al., 2006).