Crude glycerin and cottonseed cake replacing common energy and protein sources on the metabolism of feedlot lambs

This study proposed to evaluate the effects of replacing ground corn by crude glycerin and soybean meal by cottonseed cake, in association or not, on nutrient intake, apparent digestibility, feeding behavior, ruminal fermentation, nitrogen utilization, and blood metabolites of feedlot lambs. Eight ruminally-cannulated lambs (average age: 1 year; initial body weight: 51.10 ± 8.94 kg) were randomly distributed in a 4 × 4 double Latin square design, in a 2 × 2 factorial scheme, with 21-day periods (last six days for data collection). Four experimental diets were tested with different sources or combinations of energy and protein ingredients in the concentrate, respectively: 1) ground corn and soybean meal; 2) ground corn and cottonseed cake; 3) crude glycerin and soybean meal; 4) crude glycerin and cottonseed cake. An interaction effect between energy and protein sources occurred on nutrient intake and digestibility of ether extract (EE; P < 0.05). The lowest values of nutrient intake other than EE were observed in lambs fed with crude glycerin (P < 0.05). Higher intake of neutral detergent fiber (NDF) was observed in lambs fed with cottonseed cake (P < 0.05). Higher apparent digestibilities of crude protein (CP) and EE, and lower non-fibrous carbohydrates (NFC) and total digestible nutrients (TDN) were observed in lambs fed with crude glycerin (P < 0.05). No differences were observed in the time spent in feeding, rumination, idling activities, chewing, number and time per period spent doing the activities, as well as the feeding and rumination efficiencies of DM and NDF (P > 0.05). Diet and time effects were observed on ruminal fermentation parameters (P < 0.05). An interaction effect occurred between the energy source and time was observed for pH, acetate, and butyrate concentrations, and acetate:propionate ratio (P < 0.05). Lambs fed with crude glycerin showed lower intake and fecal excretion of nitrogen than those fed ground corn (P < 0.05). The triglyceride concentration was affected by the energy source (P < 0.05); with higher concentrations being observed when crude glycerin replaced ground corn. Furthermore, there was an interaction effect between energy and protein sources in the concentrations of total proteins (P < 0.01) and globulin (P < 0.01); with lower values in diets with ground corn and cottonseed cake. Cottonseed cake can replace 100% of soybean meal in diets without affecting the ingestive behavior and metabolism of feedlot lambs. On the other hand, replacing 100% ground corn with crude glycerin has potential for use in lamb feedlot diets; however more studies need to be performed. Furthermore, we recommend the use of these alternative sources, since the combination of crude glycerin and cottonseed cake can replace 100% of ground corn and soybean meal in sheep diets.