Níveis de nitrogênio não-protéico e silagens de diferentes híbridos de milho na dieta de bovinos de corte / Non protein nitrogen levels and different corn silage hybrids in beef cattle diets

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The present work was developed based on four experiments that were conducted at the experimental, research, and extension center (CEPET) of the Federal University of Viçosa, Brazil, during April to July of 2004. Experiments 1 and 2 were conducted aiming to evaluate the effects of dietary non protein nitrogen (NPN) levels on animal performance, intake and digestibility of nutrients, ruminal characteristics, N balance and microbial protein synthesis in crossbreed steers (Holstein x Zebu). Exp. 1 was conducted with 24 Holstein x Zebu crossbred steers (350 20 kg of BW) distributed in 6 randomized blocks to evaluate intake and digestibility of nutrients and performance. The diets consisted of 70% corn silage and 30% concentrate, and were formulated to be 12.5% CP (DM basis). Treatments consisted of 0, 15.5, 31, and 46.5%of NPN of dietary N. There were no treatment differences in the daily intakes of DM (P = 0.47), OM (P = 0.60), CP (P = 0.24), non-fiber carbohydrates (NFC) (P = 0.74), and TDN (P = 0.63); however, NDF intake decreased linearly as NPN increased (P = 0.02). Additionally, no effects of NPN were observed on apparent total tract digestibility of DM (P = 0.50), OM (P = 0.53), NDF (P = 0.63), and NFC (P = 0.44). The CP apparent digestibility increased linearly (P = 0.01) but ADG (1.14 kg/d) was not influenced (P = 0.96) as NPN increased. In Exp. 2, 4 ruminally and abomasally cannulated steers (300 55 kg of BW) were used in a 4 × 4 latin square design and fed with the same diet used in exp. 1 to evaluate the effects of NPN levels on intake and digestibility of nutrients, ruminal characteristics, N balance, and microbial efficiency. There were no differences in the daily intakes of DM (P = 0.22), OM (P = 0.17), CP (P = 0.31), NDF (P = 0.29) and TDN (P = 0.49). However, NFC intake increased linearly (P = 0.02) and there was a quadratic effect (P = 0.01) on EE intake as NPN increased. Ruminal digestibility of CP increased linearly (P = 0.01) with the increase of dietary NPN. There was no NPN effect on ruminal pH values (P >0.05). On the other hand, ammonia-N concentration was affected quadractly (P = 0.013) by sampling times by NPN levels interactions with maximum ammonia N of 14.6, 19.5, 18.1, and 25.4 mM at 3.3, 3.5, 3.1 and 3.8 h after feeding to diets with 0, 15.5, 31, and 46.5% of NPN, respectively. As dietary NPN increased, urinary N and urea increased linearly (P= 0.01). The N balance as % of ingested, and, as % of digested also had linear increase as dietary NPN levels increased. There were no differences (P ≥ 0.28) on microbial protein synthesis and microbial efficiency among the treatments. Dietary NPN levels up to 46.5% of total N can be fed to crossbreds steers (Holstein x Zebu) with ADG close to 1.0 kg, receiving corn silage-based diets without affecting performance and ruminal protein synthesis. However, efficiency of N utilization may decrease significantly. The third and fourth experiments were realized involving a 2 x 2 factorial arrangement of treatments to evaluate the effects of corn silages hybrids Agromen (AGN35-A42) and Bayer (A3663) and concentrate levels (25 and 50%) on animal performance, digestibility, ruminal characteristics, N balance and microbial efficiency on crossbred steers. Exp. 3 was conducted with 24 Holstein x Zebu crossbred steers, averaging 335 30 kg of BW, distributed in six randomized blocks to evaluate intake and digestibility of nutrients and performance. Treatments consisted of 75% of corn silage A + 25% of concentrate (A25), 50 % of corn silage A + 50% of concentrate (A50), 75% of corn silage B + 25% of concentrate (B25), 50 % of corn silage B + 50% (B50), on DM basis, and were formulated to be isonitrogenous (13% CP, DM basis). There were no treatment differences (P >0.05) in the daily intakes of DM, OM, and CP. However, there was a concentrate effect on NDF intake which was lower to steers fed 50% of concentrate than those fed 25% (P <0.0001). Additionally, there was a concentrate effect on NFC and TDN intakes (P <0.01), with higher intakes to steers fed diets with more concentrate. The ether extract (EE) intake was affected by silage (P = 0.02) and was higher to corn silage hybrid A than corn silage hybrid B. No treatments effects (P >0.05) were observed on apparent total digestibility of CP, EE, NDF, and NFC. On the other hand, there was a concentrate effect on total apparent digestibility of DM (P = 0.02) and OM (P = 0.01), which were greater to steers fed diets with 50% of concentrate. However, ADG (1.10 kg/d) and feed efficiency (8.13) were not influenced (P >0.05) by treatments. In Exp. 4, four ruminal and abomasal cannulated steers (512 25 kg of BW), were used in a 4 × 4 latin square design and fed with the same diet used in the exp. 3. The intake and digestibility of nutrients, ruminal characteristics, N balance, and microbial efficiency were evaluated. There were no differences (P >0.05) in the daily intakes of DM, OM, CP, and EE. However, the intakes of NDF, NFC, and TDN were affected (P <0.05) by concentrate levels, with greater intakes of NFC and TDN and lower intake of NDF to steers fed diets with 50% of concentrate than those fed 25%. The total digestibility of DM, OM and the content of TDN of diets were affected by concentrate levels (P <0.05), which were greater to diets with 50% of concentrate than those with 25%. Ruminal and intestinal tract digestibility of DM, OM, CP, EE, NDF and NFC were not affected (P >0.05) by treatments. In the same way, there were no effects of treatments on ruminal pH and ruminal ammonia-N concentration (P >0.05). In addition, N balance and microbial efficiency were not affected by treatments (P >0.05). The utilization of either corn silage hybrids evaluated in association with 25% of concentrate is a good option to feed crossbreds steers (Holstein x Zebu) with ADG close to 1.0 kg, resulting in a reduction of diet cost. The association of either corn silage hybrids evaluated with 25 or 50% of concentrate not affects ruminal pH and ruminal ammonia-N concentration, N balance, and microbial efficiency.

ASSUNTO(S)

bovino de corte uréia proteína protein avaliacao de alimentos para animais nitrogênio não-protéico urea beef cattle non-protein nitrogen

ACESSO AO ARTIGO

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