Apparent digestibility, rumen metabolism and nitrogen balance in lambs fed high-concentrate diets containing increasing levels of ground cottonseed

Abstract Text: The objective in this trial was to determine the effects of feeding ground cottonseed (GCS) on apparent digestibility, rumen metabolism and nitrogen balance. Five ram lambs, Dorper x Santa Inês (45.2 ± 0.8 kg), cannulated in the rumen, were allotted in a 5x5 Latin Square design. Each experimental period lasted 22 days, 17 days for adaptation and 5 days for sampling. Diets were isonitrogenous (15% CP, DM basis) and composed of 90% concentrate and 10% coastcross hay. Treatments were defined by the levels of GCS inclusion: 0, 7, 14, 21 or 28% (DM basis). Diets were fed ad libitum and total feces and urine were collected. On the last day of sampling, the rumen content was sampled every two hours during 12 hours, starting before feeding. The data were analyzed as repeated measures over time by using the MIXED procedure (SAS Inst. Inc.)  The LSMEANS option was used to generate individual diet means. Orthogonal polynomials for diet responses were determined by linear, quadratic, and cubic effects. Apparent digestibilities of DM (80.7, 77.3, 79.2, 76.2 and 74.4%), OM (82.3, 78.8, 80.8, 77.7 and 76.2%), CP (81.4, 80.9, 81.8, 79.3 and 79.7%) and NFC (89.4, 82.6, 84.0, 78.8 and 80.7%) were linearly reduced (P < 0.05) and EE (89.7, 93.3, 94.4, 95.0 and 93.7%) was linearly increased (P < 0.05) while NDF was not affected. Total SCFA (90.5, 95.7, 96.5, 83.4 and 71.7 mM) and propionate (35.1, 34.5, 36.4, 31.4 and 24.7 mM) had quadratic response (P < 0.05) with higher values for the inclusion of 14%. Acetate (47.4, 50.4, 47.8, 43.3 and 38.4 mM) had a linear decrease (P < 0.05) and pH (5.4, 5.5, 5.4, 5.6 and 5.7) showed a linear increase (P < 0.05). Isobutyrate, butyrate, acetate:propionate ratio and ammonia were not affected (P > 0.05). Nitrogen intake and excretion were linearly reduced (P < 0.05) resulting in no effect on retained nitrogen (P > 0.05). The inclusion of GCS affected negatively DM, OM, CP and NFC apparent digestibilities. Propionate and SCFA were higher  with the inclusion of 14% of GCS. 

Keywords: Co-product, SCFA, Rumen ammonia nitrogen