Rumen Morphometrics of Nellore Cattle Submitted to Either Nutritional Restriction or Intake of Concentrate Feedstuffs Prior to Adaptation Period

The study, conducted at São Paulo State University feedlot, Dracena campus, Brazil, was designed to evaluate the effects of either nutritional restriction or intake of concentrate feedstuffs before beginning the adaptation period on rumen morphometrics and rumenitis of Nellore cattle. The experiment was designed as a completely randomized block, replicated 8 times (4 animals/pen), in which 96 22-mo-old yearling Nellore bulls (365.5 ± 39.2 kg) were fed in 24 pens according to the treatments: Restriction (Tifton hay fed at 1.4% of BW + mineral supplement); Control (Tifton hay fed ad libitum + mineral supplement) and Concentrate (Tifton hay fed ad libitum + 0.5% of BW of a mix of concentrate feedstuffs and mineral supplement). This study lasted 144-d, divided into 2 periods: 32-d of pre-adaptation, in which cattle were submitted to the treatments previously described, and 112-d of feeding high-concentrate diets, where cattle were fed the same diets. The adaptation program consisted of ad libitum feeding of two diets over adaptation period with concentrate level increasing from 72% to 86% of diet DM. The finishing diet contained: 73.5% cracked corn grain, 14.0% sugarcane bagasse, 9.0% cottonseed meal, 1.5% supplement, 1.2% urea and 0.8% limestone (DM basis). At the end of pre-adaptation period, one animal per pen (n=24) was slaughtered for rumen evaluations. The remaining 72 animals were harvested after 112-d of feeding high-concentrate diets. At harvest, rumenitis was determined, on the entire washed rumen, using a scale of 0 (no lesions noted) to 10 (severe ulcerative lesions). A 1-cm² fragment of each rumen was collect from cranial sac. The number of papillae per cm² of rumen wall (NOP) was determined, as well as the mean papillae area (MPA). The rumen wall absorptive surface area (ASA) was calculated, as follows: 1+(NOP*MPA)-(NOP*0.002). No significant (P > 0.10) treatment effect was observed for rumenitis (Restriction=1.65, Control=1.79, Concentrate=1.55). Cattle submitted to nutritional restriction had greater (P < 0.10) NOP (Restriction=72.76^a, Control=63.28^b, Concentrate=62.99^b) and larger ASA in cm² (Restriction=26.89^a, Control=22.29^b, Concentrate=22.30^b). Also, a significant (P = 0.05) interaction between treatment and period was observed for MPA, where no differences were observed at the end of pre-adaptation period, but cattle submitted to nutritional restriction presented larger MPA than animals in a control group after 112-d of feeding high-concentrate diets. Thus, cattle should be submitted to nutritional restriction prior to period of feeding high-concentrate diets, because it led to greater rumen epithelium development.