We evaluated the differences between the supplementation of urea in rumen and/or abomasum on forage digestion, nitrogen (N) metabolism, and urea kinetics in cattle fed a low-quality tropical forage. Five Nellore heifers were fitted with rumen and abomasum fistulas and assigned to a Latin square design. The treatments were: control, continuous infusion of urea in the abomasum (AC), continuous infusion of urea in the rumen, a pulse dose of urea in the rumen every 12 hours (PR), and a combination of PR and AC. The control exhibited the lowest (P<0.10) fecal and urinary N losses, which were, overall, increased by supplementation. The highest urinary N losses (P<0.10) was observed when urea was either totally or partially supplied as a ruminal pulse dose. The rumen N balance was negative for the control and when urea was totally supplied in the abomasum. The greatest microbial N production (P<0.10) was obtained when urea was partially or totally supplied in the abomasum. Urea supplementation increased (P<0.10) the amount of urea recycled to the gastrointestinal tract and the amount of urea-N returned to the ornithine cycle. The greatest (P<0.10) amounts of urea-N used for anabolism was observed when urea was totally and continuously infused in the abomasum. The continuous abomasal infusion also resulted in the highest (P<0.10) assimilation of microbial N from recycling. The continuous releasing of urea throughout day either in the rumen or abomasum is able to improve N accretion in the animal body, despite of mechanism responsible for that being different.

<p>Genetics differences between breeds may determine the tolerance to high temperature, effect dry matter intake and consequently cattle performance. The effect of temperature and humidity index (THI) on diurnal, nocturnal and daily intake, water intake, physiologic parameters and behavior of Nellore (<em>B. indicus</em>) and Angus (<em>B. taurus</em>) bulls were evaluated. Eight Angus and eight Nellore young bulls (337±7.4 kg and 16 months of age) were allocated in two climate-controlled rooms for 32 days. In the period 1, all bulls were housed in thermoneutral conditions (TN, THI = 72.6) for 10 days. In period 2 (10 days), four Angus and four Nellore bulls were subjected to low heat stress (LHS, THI = 76.4) in daytime, and four Angus and four Nellore bulls were subjected to high heat stress (HHS, THI = 81.5) in daytime. The diurnal and daily dry matter intake (DMI) of Nellore were not affected (P&gt;0.05) by heat stress. However, Angus bulls decreased diurnal DMI by 24% and daily DMI decreased (P&lt;0.05) by 15% on HHS. In TN Angus bulls had higher (P&lt;0.05) daily DMI (36.2 g/kg of BW) than Nellore (29.1 g/kg of BW), but in HHS they had similar (P&gt;0.05) daily DMI (31.6 and 30.2 g/kg of BW, respectively). We observed an increase (P&lt;0.05) in respiratory frequency, but water intake was not affected (P&gt;0.05) by heat stress. The heart rate decreased (P&lt;0.05) with heat stress. No differences were found (P&gt;0.05) in feeding behavior. Therefore, THI stress threshold should distinct for Angus and Nellore bulls. The use of feed intake information may improve the prediction of thermic discomfort on specific climate condition. </p>

The objectives of this study were to test the interaction of breed (Nellore or Angus) and diet (whole shelled corn [WSC] or ground corn [GC] with silage) on growth performance, carcass characteristics, and ruminal pH of young bulls. Thirty-six bulls (18 Nellore and 18 Angus) with the range in age of 18 to 22 mo and BW of 381 ± 12 kg were used in a completely randomized design experiment with a 2 × 2 factorial arrangement of treatments (2 breeds and 2 diets). Experimental diets (DM basis) included 1) a GC diet containing 30% corn silage and 70% GC- and soybean meal-based concentrate and 2) a WSC diet containing 85% WSC and 15% of a soybean meal- and mineral-based pelleted supplement. An additional 8 bulls were slaughtered at the beginning of the experimental period for determination of initial carcass weight. The treatments were Nellore fed the GC diet, Nellore fed the WSC diet, Angus fed the GC diet, and Angus fed the WSC diet. Greater DMI ( < 0.01), ADG ( < 0.01), and G:F ( < 0.01) were observed in Angus bulls compared with Nellore bulls, regardless of diet. Lower average ruminal pH ( = 0.04), maximum ruminal pH (P = 0.02), and DMI ( < 0.01) were observed in bulls fed the WSC diet than in those fed the GC diet. In addition, bulls fed the WSC diet had greater G:F ( < 0.01). The WSC diet led to greater variation in DMI compared with the GC diet ( < 0.01). Omasum and large intestine percentage was affected by diets only in the Angus breed ( < 0.02) and were greater when bulls were fed the GC diet. The WSC diet without forage may be useful for feedlots because this diet promoted greater G:F than the GC diet, regardless of breed. However, special care must be exercised in feed management during adaptation and throughout the feeding of Nellore animals to avoid digestive disorders and fluctuations in DMI.

This study aimed to evaluate the quality traits and fatty acid profile of beef from Nellore and Angus bulls fed whole shelled corn (WSC) and ground corn plus maize silage (GC) diets. Eighteen Nellore and 18 Angus young bulls [381 ± 12 kg initial body weight (BW) and an average age of 20 ± 1.9 months] were used in a completely randomized design using a 2 × 2 factorial arrangement and were slaughtered at a final BW of 451.5 kg and 545.5 kg, respectively. Twenty-four hours after slaughter, samples of longissimus thoracis muscle were collected for the analysis of lipid oxidation, color, fatty acid profile, shear force, and cooking loss. There was no effect of diet × breed interaction on meat color, lipid oxidation, shear force, and cooking loss. Angus beef had lower shear force (p < 0.05) than Nellore beef and had a greater concentration of linoleic acid and polyunsaturated fatty acids (PUFA) (p < 0.01). Beef of bulls fed WSC tended to have greater concentration of CLA C18:2c9t11 (p = 0.09), greater concentration of CLA C18:2t10c12 (p = 0.01), and PUFA (p = 0.05), and consequently, higher oxidation levels. Angus bulls produced beef with greater tenderness and PUFA concentration.The results of fatty acid show a possible change in biohydrogenation when animals are fed the WSC diet, reducing lipogenesis, as this diet increases the C18:2t10c12 content.

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