Cotton crop residues are sometimes used to feed cattle and sheep, notably in cotton producing countries such as India and Egypt. These residues are of poor nutritive value. A low OM digestibility value (37%) has been reported in sheep, both for unprocessed cotton straw or after treatment with ammonia or NaOH (Flachowsky et al., 1981). A comparison between various crop residues found cotton crop residues to have a very poor DM degradability (7%), much lower than that of maize stover (37%) (Rao et al., 1995). For that reason, cotton crop residues are not used as a sole feed and various processes have been proposed, including mechanical processes (grinding, extrusion-pelleting), chemical treatments (NaOH, NH3, CaOH, ozone), and biological treatments (ensiling, treatment with fungi) in order to improve intake and nutritional value. However, the improved performance and revenue may not compensate the cost of these treatments.
Ground cotton straw included as the only roughage source (40%) in a complete diet with concentrate (60 %) was fed to growing young (6-9 months) crossbred calves (74 kg) for 180 days. The average DM intake of the diet was 108 g/kg W0.75 and the daily weight gain 627 g/d. When ground cotton straw was processed with an expander-extruder pelletizer before being included at the same level into the diet, both DM intake and daily weight gain increased: 113 g/kg W0.75 and 815 g/d respectively. When ground cotton straw was offered separately with concentrates, DM intake and daily weight gain (97 g/kg W0.75 and 465 g/d respectively) were lower than when cotton straw was included into the diet. The results indicated that the unprocessed cotton straw was less palatable and had a slower rate of passage through the rumen than the processed straw (Kirubanath et al., 2003).
When cotton straw was used as the sole roughage (45%) in a total mixed ration offered to calves (158 kg), pelleted cotton straw significantly increased DM and OM digestibility of the diet compared to ground material (53 and 54% vs. 50 and 51% respectively), but not the digestibility of the fibre fractions (NDF, ADF). Ground cotton straw treated with ammonia included (45%) in a complete diet significantly increased DM intake (2.7-2.8% of body weight) and daily weight gain (930-974 g/d) compared to untreated cotton straw (2.6% live weight and 796-878 g/d) (Narasa Reddy et al., 1985).
Cotton crop residues can be grazed (cotton lint and leaves and to a lesser extent stalks) by dry gestating cows allowing them to maintain live weight and body condition score until the lint and leaves are fully consumed. When animals start to lose weight or body condition score, they have to be removed from the field. It can be assumed that about 0.4 ha can maintain dry cows for 30 to 40 days (Stewart, 2010).
In dairy buffaloes, expanded cotton straw fed for 180 days at 30% of a complete pelleted diet, in which it was the sole roughage, was compared to a conventional diet based on concentrate and sorghum straw. Dry matter intake and milk yield were similar but the diet containing expanded cotton straw gave the higher milk fat content (Nagalakshmi et al., 2004).
Cotton straw (ground or as expanded-extruded pellets) was included (50%) in a complete diet with concentrates for sheep (28.3 kg) and compared to ground cotton straw offered separately with concentrates. Dry matter intake was higher with expanded extruded pellets (4.8% live weight), or when ground and mixed into the diet (3.9%), than when offered separately (3%) (Kishan Singh et al., 2003). Ensiling of cotton stalks treated with fungi (oyster mushroom Pleurotus ostreatus) increased the protein content, decreased fibre content and improved nutrient digestibility in rams (Hamza et al., 2006).