In temperate countries, maize stover is generally considered as an adequate energy source for beef cattle, including heifers, steers, and cows, as well as maintenance and gestating ewes (Jordan, 1990; Russell, 1986 ; Jean et al., 2017a ; Kyle, 2011 ; Kyle, 2015). However, due to the relative low value of this forage and to its variability over time, ration balancing is critical when factoring stover into cattle diets, and a proper supply of energy, protein and minerals must be provided to meet nutrient requirements and performance goals (Jean et al., 2017b). In tropical and dry climate countries, maize stover is widely used for all types of livestock. In the central Kenya highlands, for instance, maize stover is the most abundant crop residue and it is often the sole forage offered to dairy cattle during the dry seasons (Methu et al., 2001).
Palatability
Maize stover has a large particle size, and livestock tend to sort through it to eat the smaller parts first - grain, cobs and leaves - and leave the stalks. In sheep, refusal up to 25-30% have been observed (Jordan, 1990). When maize stover is added to a total mixed ration, because cows can readily sort through the TMR, leaving the corn stalks in the bunk and having lower fiber intake than anticipated. Therefore, reducing the particle size before or during mixing will be important in reducing the risks for sorting (Eastridge, 2007).
Digestibility
The digestibility of maize stover is the highest at grain harvest and declines over time. A trial in Canada found that the in vitro DM digestibility started at 52% and then declined by 1.5 percentage point per week (Leask et al., 1973). Another trial in the USA also found that a reduction in in vitro DM digestibility for the fibrous parts of maize stover, with losses of 15-20 percentage points over three months, though the total yield of digestible DM decreased only slightly (Weaver et al., 1978). This reduction in digestibility does not seem to result primarily from increased lignification of the cell walls, but from an increase in the concentration of NDF because of the loss of cell solubles (Russell, 1986).
Grazing
Grazing maize stover can provide a low cost feed source for mid-gestation beef cows and maintenance and mid-gestation ewes, who can also glean the grains and cobs left on the field. About 50 cows can graze on 20 ha, or 20-25 ewes per ha, for one to two months. Because the animals tend to eat the kernels and cobs first, it may be necessary to restrict the grazing time or size so that the cows do not overload on grain, and to keep the energy intake more uniform. As the nutritive value of the stover decreases over time, so supplementation with hay will be required to meet protein and energy requirements, notably when the cows have eaten all the leftover grain. In automn and winter, it is important to pay attention to soil condition by having the animals graze only dried or frozen fields, and preventing them from grazing wet (thawed) ones (Kyle, 2015).
Cut and carry
Beef cattle
The utilisation of maize stover for beed cattle has been extensively studied in the United States. In Michigan, finishing steers in a feedlot operation could be fed a ration with up to 20% maize stover (DM basis) without significantly effecting performance. Cattle compensated for a lower energy diet containing less maize grain by increased intake when fed a 20% stover diet. Feeding stover had a significant effect on DM intake, but the carcass characteristics and weight gain remained similar among treatments (Jean et al., 2017a). In a trial in Nebraska, steers fed early harvested maize stover gained 180 g/d more and were 19% more efficient than those fed the late harvested stover (Berger et al., 1979).
Several studies have investigated the use of alkali treatment for improving the nutritive value of maize stover. In Indiana, several trials studied the value of ammoniated maize stover with positive conclusions. In 240 kg steers fed 900 g/d of grain, stover treated with ammonia at 2 or 3% DM increased DM intake, DM digestibility, and N retention compared to unammoniated stover fed with the same amount of supplement. Mature pregnant beef cows fed a similar diet with stover treated at 3.2% DM had higher weight gains and their condition score did not decrease unlike that of cows fed untreated stover or other diets, (Saenger et al., 1982). Treatment with NaOH of late harvested stover improved steer performance, increasing gain by 220 g/d and feed efficiency by 26%. The effect of NaOH treatment was less conclusive for early harvested stover, as it had no effect in one trial and was satisfying in another, where it increased gains by 210 g/d and feed efficiency by 20% (Berger et al., 1979).
However, NaOH is expensive, corrosive, poses human health risks, and the treated feeds may provide excess dietary sodium, so alternative methods, and particularly treatments with calcium oxide (CaO, quicklime) are now preferred. It has been shown that treatment of stover with 7% CaO and addition of water to 50% DM resulted in nine times greater release of glucose and xylose after incubation with cellulase (Donkin et al., 2013). Similar feedlot performance was achieved when high moisture and dry rolled maize grain was replaced by CaO-treated maize stover to a level of 20% of the ration (Shreck et al., 2012). When steer calves were fed CaO treated (5% of DM) or untreated maize stover with wet distillers grains plus solubles, treatment with CaO failed to improve performance and it was concluded that not treating maize stover was more economical (Shreck et al., 2014).
Dairy cows
In temperate countries, maize stover has limited use as a feed resource for lactating dairy cows given its low nutritional value but studies carried out since the 2010s have shown the potential of using CaO-treated maize stover in dairy diets (Casperson et al., 2018). The combination of CaO-treated maize stover and dried distillers grains could replace wild rye, maize silage, or maize grain to a level of 15% of diet DM without affecting DMI, milk production, or 4% FCM yield (Shi et al., 2015). However, replacing grain in the diet with alkali-treated maize stover at 13% of the diet DM reduced DMI and milk production (Cook et al., 2016). Short term studies indicate that maize stover treated with 5% CaO and added water to 50% dry matter can replace maize silage in diets for lactating dairy cows to at least 25% of the total ration (Donkin et al., 2013).
In tropical and dry climate countries, maize stover is sometimes the main forage fed to dairy cattle during the dry season. In central Kenya, the stover is usually chopped and offered as the sole forage, but depending on availability, the stover may be mixed with weeds or any available green materials. Stover is sometimes alternated with elephant grass to ensure that the latter is available for as long as possible. Offering maize stover in excess to dairy cattle was found to be an effective strategy to improve the intake of maize stover supplemented with cottonseed cake and increase milk production. (Methu et al., 2001).
Sheep
Feeding maize stover has been described as an opportunity to reduce the cost of feeding ewes during early gestation. However, it was found to be poorly palatable, with a 25-35%. Ewes weighing 80-90 kg consumed only 900 g/day of stover. Grinding the stalks increased intake by 10-15%, but the grinding costs ($10-15/t ) made maize stover less economically appealing. To utilize maize stover, it is recommended to supplement with either a protein and mineral supplement, or about half of the DM must be provided as alfalfa hay (Jordan, 1990).
Early studies indicated that pretreatment of corn stover with a combination of 2% NaOH and 2% CaO resulted in a 53% increase in feed intake in growing lambs and a 12% increase in DM digestibility (Oji et al., 1977). More studies indicate a 6 to 9% increase in total tract DM digestibility in lambs fed maize fibre pretreated with a combination of alkali and heat (Donkin et al., 2013).
Silage
Ensiled maize stover, when stabilized after 1 or 2 months, are comparable to a regular hay. Supplementation with protein-rich feed is necessary to fulfill animal requirements. Adding 10 g or urea per kg DM may allow a better nitrogen balance. When the DM content is lower than 30%, ammonia treatment is possible using the same process as the one used for whole-plant maize silage (CNC, 2002). Ensiled maize stover is mainly valuable for beef cattle and sheep, and of little value of dairy cows.
Beef cattle
It may form the basis of the diet of suckler cows at the end of gestation and at the beginning of lactation, and of beef heifers during winter. Suckler cows and beef heifers can eat 1.4-1.7 kg DM per 100 kg of liveweight of ensiled maize stover. For instance, a diet for beef cows may include up to 35-40 kg/day of ensiled stover. Young steers (> 240 kg) can consume up to 15-20 kg/day of that forage. In all cases, supplementation with protein sources, minerals and vitamins is necessary (CNC, 2002).
In Nigeria, ensiled maize stover treated with 4% urea fed to native Zebu cattle was found to be have a higher OM digestibility than the untreated silage (65% vs 51%) and to increase intake, but it did not prevent cattle weight loss (Alhassan et al., 1991).
Sheep
A comparison of various treatments of maize stover silage fed to sheep concluded that ammonia treatment (3%) was more effective in enhancing the DM intake by sheep than treatement with urea or poultry litter. However, treated or untreated maize stover always resulted in a lower DM intake than that obtained with the basal diet (Ali et al., 2009).
Green stover tops
Recent advances in feeding strategies include the use of green maize stover tops as fodder, sometimes supplemented with grain legume crops (Bwire et al., 2002). In Tanzania, green maize stover tops (including leaves and tassels) can be offered as feed to dairy cattle in semiarid regions during the dry season. Time of harvesting affected nutritive value, due to the rapidly declining quality when plant matter remains on the field (Shirima et al., 1994 cited in Bwire et al., 2002). Harvesting maize stover tops when still green led to higher OM digestibility (62-65%), crude protein level (5.2-5.9% DM) and metabolizable energy (8.6-9.0 MJ/kg DM) compared to later stages. Storing maize stover tops in a shed preserved nutritive value much better than laying and stacking them in the field. Green maize stover tops supplemented with lablab forage led to performance similar to that obtained with a grass hay mixture, and to higher milk production (5 kg/d) and voluntary dry matter intake (8 kg DM/d including 5 kg of green maize stover tops) (Bwire et al., 2002).