Maize green forage is a valuable feed for ruminants in terms of yield and nutritive value (Sarap et al., 2015), though supplementation can be needed to compensate for its low protein, mineral and vitamin contents (Bwire et al., 2002; Tauqir et al., 2013). Maize forage is particularly effective in optimizing milk yields of dairy cows (Brewbaker, 2003).
Digestibility and energy values
Digestibility and nutritive value of the whole maize plant, fresh or ensiled, have been widely studied, especially using sheep (see references in Andrieu et al., 1974). The feed value of maize is much greater (up to 35% more) when the whole plant is harvested (Brewbaker, 2003). From flowering to grain maturity, the whole plant shows a quite constant OM digestibility (71-72%), because the increasing proportion of maize ear, which has a high and constant digestibility (83%), compensate for the decreasing digestibility of the rest of the plant (from 70% to 60%; Demarquilly, 1969 cited in Demarquilly et al., 1992). The best predictor of the whole plant digestibility is its undigestible cell wall content, as for other forage crops (Andrieu et al., 1993). Digestibility does not vary much with variety or with seeding rate. However, maize varieties selected for their quality or including the Brown Midrib gene, which decreases the plant lignin content, can result in digestibility higher by 3 to 5 points (Demarquilly et al., 1992). Some sterile varieties have existed, which were well ingested due to their high soluble sugar content, though their OM digestibility was lower than that of fertile varieties (e.g. 65% for the “sucrensilage” variety in Andrieu et al., 1974). In India, in vitro OM digestibility (83 vs. 79%) and ME (10.2 vs. 9.2 MJ/kg DM) were higher for fresh baby corn forage than for baby corn silage (Bakshi et al., 2012).
Maize green forage is not commonly fed to dairy cattle in Europe, but is used for that purpose in tropical regions. In India, it was shown that for low productive dairy cattle (5 kg/d of milk), 1 kg concentrate mixture can be replaced by 10 kg of maize green forage maize without affecting daily milk production provided that the animal is also offered ad libitum roughage such as straw. Total intake was 3.86 kg DM/100 kg LW including 0.8 kg DM/100 kg LW of concentrate, 1.6 kg DM/100 kg LW of maize green forage and 1.4 kg DM/100 kg LW of sorghum straw. Body weight gain was 11 kg over 45 days, and average milk yield was 4.9 kg/d. The higher level of inclusion of maize green forage as a replacement of concentrate in the diet resulted in a lower cost of feed and in a higher net profit per animal per day (Naik et al., 2012).
Maize green fodder is not commonly fed to growing cattle in Europe but is considered valuable for that purpose in India, in the USA and in Canada (Sarap et al., 2015; Potter, 2012; Newport, 2006). In India, crossbred heifers solely fed on green maize leaves (26% DM) showed a DM digestibility of 65% and a DM intake of 3.94 kg DM/100 kg LW. Total body weight gain was 53 kg, indicating that the green maize leaves as a sole feed was enough for satisfactory maintenance and growth (Sarap et al., 2015). In Pakistan, the DM intake and DM digestibility of maize green forage fed to 18-20 months Sahiwal heifers was 5.87 kg DM/100 kg LW and 62% respectively. Supplementation with urea/molasses increased feed intake (6.36 kg DM/100 kg LW) but not DM digestibility. Daily weight gain was higher for heifers given maize fodder and urea (0.77 kg/d) compared to green maize fodder alone (0.58 kg/d) (Tauqir et al., 2013). In Mississippi, heifers grazing maize green forage gained more than 1 kg/day and the pasture sustained a total weight gain of 500kg/ha in only 75 days (Newport, 2006).
In India, nutrient digestibility of fresh baby corn husks fed ad libitum to male Murrah buffalo calves was higher to that of green maize forage but DM intake was lower. Retained nitrogen was also higher for baby corn husks. When offered as a total mixed ration with wheat straw and concentrate mixture, baby corn silage enabled even higher nutrient digestibility, voluntary intake and N retention. Baby corn husks were a highly acceptable and palatable forage as compared to conventional maize fodder (Bakshi et al., 2012).
In Europe, whole maize plants harvested after flowering were characterized from 82 trials with sheep: mean DM content was 23% (14-33%); mean OM digestibility was 72% (67-80%); mean DM intake was 53 g DM/kg LW0.75 (38-67 g DM/kg LW0.75)(Demarquilly et al., 1992). At later stages, OM digestibility increased from 67% to 69% from milk stage to full maturity, while DM intake decreased from 72 to 61 g DM/kg LW0.75 (Kirilov, 1999). In early studies with sterile maize in France, sterile maize green forage had a lower digestibility but intake by sheep was higher (on the average 20% more) than for fertile maize. Sheep ingested between 53 and 71 g DM/kg LW0.75, depending on plant maturity and experimental site. Male-sterile maize green forage was found valuable because its nutritive value did not vary much after flowering and intake remained high, provided that DM content was over 18% (Andrieu et al., 1974).
In India, Barbari goats offered maize green forage harvested at blooming stage (including leaves, leaf sheath, stems and inflorescences) (allowance of 20% refusals) ingested 40 g DM/kg LW0.75 (i.e. 37 g OM/kg LW0.75) resulting in 0.21 kg of weight gain over the week. DM and OM digestibility were 75% and 76% respectively. Increasing allowance to 35% and 50% refusals resulted in higher digestibility (81% and 82% for DM and OM digestibility respectively), higher DM intake (51 and 66 g DM/kg LW0.75 for 35% and 50% refusals respectively) and higher weight gains (0.30 and 0.35 kg/week). Allowing selective consumption at higher allowance levels, maize green forage was found not only to meet maintenance requirements but provided surplus energy and protein for production (Dutta et al., 2000).