Intake and digestibility in cattle under grazing supplemented with nitrogenous compounds during dry season

Abstract

-The objective of this work was to evaluate the effects of supplementation with nitrogenous compounds on intake and digestibility in cattle under grazing during dry season. It was used five Holstein × Zebu steers with average initial live weight of 236 kg, kept in five Brachiaria decumbens Stapf. paddocks (0.34 ha). The experiment was carried out according to a 5 × 5 Latin square design, with five supplementation levels and five experimental periods. The supplementation levels were the following: 0; 0.35; 0.70; 1.05, and 1.40 g of crude protein/kg live weight. A mixture of urea, ammonium sulfate and albumin (4.5:0.5:1.0, respectively) was used as nitrogen supplement. The average crude protein levels in the diet were 7. 39; 8.92; 10.98; 12.55; and 13.62%, as dry matter basis, for the respective supplementation levels. Linear-response-plateau relationships were observed between intake estimates and diet crude protein levels. The linear-response-plateau pattern showed that intake was increased up to crude protein levels close to 9%, as dry matter basis. The estimates became unchangeable from this level. The total and ruminal digestibility coefficients of dry matter and neutral detergent fiber, and diet level of total digestible nutrients presented a positive linear pattern according to diet crude protein levels. The rumen ammonia nitrogen concentration was linearly increased by diet crude protein levels. This variable assumed the value of 8.00 mg/dL when the intake estimates reached the maximum values.Supplementation with nitrogen compounds in quantities that raise the crude protein content in the diet to levels close to 9% optimizes the use of low-quality forage by cattle under grazing.

Nutritional aspects applied to grazing cattle in the tropics: a review based on Brazilian results

“…Therefore, the interactive effect of nitrogen supplementation leads to the occurrence of and is characterized by sequential responses in which the increased nitrogen availability improves the synthesis of fibrolytic enzymes. In addition, the increased fiber degradation improves the availability of energy for microbial and animal (LAZZARINI, 2011) growth.…”

“…Under these circumstances, positive responses in fiber degradation will be observed with a supplementation program that allows the RAN concentration to be increased up to 8 mg/dL FIGUEIRAS et al, 2010). However, the plateau in EDF estimates observed when the RAN concentration becomes greater than 8 mg/dL seems to indicate that nitrogen supplementation does not affect fiber degradation (Figure 3).…”

“…Although there have been improvements in microbial growth on low-quality fiber diets , some experiments have demonstrated that nitrogen supplementation does not necessarily cause a significant increase in microbial flow to the intestine (LAZZARINI et al, 2009a;FIGUEIRAS et al, 2010;SOUZA et al, 2010;RUFINO, 2011).…”

“…Therefore, for most production systems, the primary alteration of the diet via supplements must be based on the addition of dietary protein to adjust the energy-to-protein ratio in the diet (Figure 8). In this case, forage intake and fiber digestibility should not change (COSTA et al, 2011b;2011c;LAZZARINI, 2011;RUFINO, 2011;BATISTA, 2012). Increased animal performance has been reported by several authors who used protein/ nitrogen supplementation (including urea as a nitrogen source) in animals grazing on mediumto high-quality forages (ZERVOUDAKIS, 2003;ZERVOUDAKIS et al, 2002;PORTO, 2009).…”

Effect of protein supplementation on ruminal parameters and microbial community fingerprint of Nellore steers fed tropical forages

“…However, the availability of foods for ruminants in the tropics varies depending on seasonality, with a distinct dry period and a rainy period (Figueiras et al, 2010;Costa et al, 2011). In the dry period (AprilSeptember), the tropical forages available for animal feeding show a high fiber and lignin content and the levels of CP are often <7%, a value considered limiting for microbial protein synthesis by ruminal microorganisms (Lazzarini et al, 2009;Figueiras et al, 2010). In the rainy period (October-March), the forages have a more adequate CP content (16%), but the synthesis of microbial protein is still limited because of the high degradability of the CP in the forages (Costa et al, 2011).…”