EFFECTS OF DAILY OR EVERY THREE DAYS PROTEIN OR PROTEIN AND STARCH SUPPLEMENTATION ON INTAKE AND DIGESTIBILITY OF NELLORE HEIFERS FED MEDIUM-QUALITY TROPICAL GRASS

The objective was to evaluate the effects of daily or every three days supplementation with protein or protein and starch on intake and digestibility in Nellore heifers fed a high-quality tropical grass. Five rumen cannulated Nellore heifers (299 ±7.5 kg of BW) were used in a 5 x 5 Latin square design. Treatments were: control, non-supplemented (CONT); 200 g of CP (Crude Protein) daily (P/D); 200 g of CP and 400 g of starch daily (PS/D); 600 g of CP every three days (P/3D); 600 g of CP and 1200 g of starch every three days (PS/3D). The basal diet consisted of a high-quality Tifton hay (Cynodon sp; 8% CP;75% NDF (Neutral Detergent Fiber)), fed ad libitum twice daily at 06h and 18h. The experiment consisted of five experimental periods, which lasted 27 days each, 15 days of adaptation to the treatments and 12 days for sample collections. Voluntary forage and digestible OM (Organic Matter) intake were quantified day 16 to 22 (covering 2 supplementation cycles). Statistical analyses were performed using the MIXED procedure of SAS 9.4. Treatments effects were interpreted according to a 2 x 2 + 1 factorial arrangement (two frequencies, daily versus every 3 days; starch supplementation, with or without; and a control treatment). Significances were declared at P<0.05. Overall, supplementation increased (P<0.02) intake of CP and digested OM (DOM), and the ratio of CP intake to DOM intake (CP:DOM). Treatments with supplementation at every 3 d (P/3D and PS/3D) had lower forage intake, which consequently decreased OM, NDF and DOM intake. Starch supplementation (PS/D and PS/3D) increased DOM intake (kg/d) and decreased CP:DOM and NDF intake (g/kg BW).The interaction between supplementation and starch addition did not affect (P>0.61) intake. Intake was affected (P<0.01) by interaction between treatments and sampling days. On the first day of the supplementation cycle, treatments with infrequent supplementation (P/3D and PS/3D) had lower forage intake (P<0.01), without differences among treatments (P?0.23) on days 2 and 3 of the supplementation cycle. Supplementation increased (P<0.01) total digestibility of OM, CP, and diet DOM content, whereas NDF digestibility was not affected (P>0.93) by treatments.