Can conventional forages be replaced with cotton plant (Gossypium hirsutum) wastes in fattening lambs? Laboratory and animal studies.

The cotton plant (Gossypium hirsutum) is a shrub native to many arid and semi-arid regions around the world, while the nutritional value of its wastes has been less scientifically investigated. Different components of whole cotton plant wastes (WCPW) including leaf blade, cotton pod, stem, root, bract, petiole, and cottonseed were evaluated for their nutritional values by standard laboratory methods. After that, we tested the WCPW for partial substitution (0, 20, 40, and 60% substitution or 0, 10, 20, and 30% of dietary dry matter (DM)) with dietary common forage in a completely randomized design with 32 feedlot male lambs for 90 days. A diverse range of chemical and mineral compositions was found among the different WCPW's components. The cottonseed had the highest crude protein (CP) and ether extract (EE) contents, while the lowest neutral detergent fiber (NDF) and acid detergent fiber (ADF) were observed in the leaf blade (P < 0.0001). The highest contents of calcium, phosphorus, sodium, magnesium, and iron were also observed in the leaf blade (P < 0.0001). Higher potential gas production, in vitro organic matter digestibility (OMD), in vitro dry matter digestibility (DMD), and total volatile fatty acids (TVFA) were also related to the leaf blade (P < 0.0001). Bract had the highest acid-base buffering capacity (P < 0.0001). The lambs fed on 30% of dietary DM with WCPW exhibited lower final body weight (BW), average daily gain (ADG), CP or NDF digestibility, ruminal TVFA, propionate, plasma total protein, and higher feed conversion ratio (FCR) compared to the control group. Generally, WCPW can be substituted up to 40% of common forages (or 20% of diet DM) without any adverse effect on growth performance and blood metabolites of feedlot lambs, especially during feed shortages.