Development of equations to estimate microbial contamination in ruminal incubation residues of forage produced under tropical conditions using 15N as a label.

The objective of this study was to use (15)N to label microbial cells to allow development of equations for estimating the microbial contamination in ruminal in situ incubation residues of forage produced under tropical conditions. A total of 24 tropical forages were ruminal incubated in 3 steers at 3 separate times. To determine microbial contamination of the incubated residues, ruminal bacteria were labeled with (15)N by continuous intraruminal infusion 60 h before the first incubation and continued until the last day of incubation. Ruminal digesta was collected for the isolation of bacteria before the first infusion of (15)N on adaptation period and after the infusion of (15)N on collection period. To determine the microbial contamination of CP fractions, restricted models were compared with the full model using the model identity test. A value of the corrected fraction "A" was estimated from the corresponding noncorrected fraction by this equation: Corrected "A" fraction (A(CP)C) = 1.99286 + 0.98256 × A" fraction without correction (A(CP)WC). The corrected fraction "B" was estimated from the corresponding noncorrected fraction and from CP, NDF, neutral detergent insoluble protein (NDIP), and indigestible NDF (iNDF) using the equation corrected "B" fraction (B(CP)C) = -17.2181 - 0.0344 × fraction "B" without correction (B(CP)WC) + 0.65433 × CP + 1.03787 × NDF + 2.66010 × NDIP - 0.85979 × iNDF. The corrected degradation rate of "B" fraction (kd)was estimated using the equation corrected degradation rate of "B" fraction (kd(CP)C) = 0.04667 + 0.35139 × degradation rate of "B" fraction without correction (kd(CP)WC) + 0.0020 × CP - 0.00055839 × NDF - 0.00336 × NDIP + 0.00075089 × iNDF. This equation was obtained to estimate the contamination using CP of the feeds: %C = 79.21 × (1 - e(-0.0555t)) × e(-0.0874CP). It was concluded that A and B fractions and kd of CP could be highly biased by microbial CP contamination, and therefore these corrected values could be obtained mathematically, replacing the use of microbial markers. The percentage of contamination and the corrected apparent degradability of CP could be obtained from values of CP and time of incubation for each feed, which could reduce cost and labor involved when using (15)N.

Desempenho e exigências de energia e proteína de bovinos de corte em pasto suplementados / Performance, energy and protein requirements of beef cattle grazing supplemented

Avaliou-se o efeito dos níveis de suplementação sobre o desempenho, as características de carcaça, a composição corporal e as exigências de energia e proteína de bovinos de corte sob pastejo. A área experimental constituiu-se de cinco piquetes formados com Brachiaria decumbens. Utilizaram-se 22 bovinos não castrados, com peso corporal médio inicial de 320kg e idade de 18 meses. Três animais foram abatidos ao início do experimento para servirem como referência. Dos 19 animais restantes, três foram designados ao grupo mantença (MT), os outros 16 foram distribuídos em quatro tratamentos: controle ou mistura mineral (MM), 1kg, 2kg e 3kg de suplemento ao dia. Observou-se aumento linear no consumo de matéria seca (CMS), energia digestível (CED) e energia metabolizável (CEM); o consumo de nutrientes digestíveis totais (CNDT) foi máximo para o consumo de 2,88kg de suplemento. O ganho médio diário (GMD) máximo, 0,91kg/dia, foi observado para o consumo de suplemento de 2,69kg/dia. Verificou-se aumento linear no peso corporal em jejum (PCJ), no peso de corpo vazio (PCVZ) e no peso da carcaça para os animais suplementados. Não foi observado efeito da suplementação sobre o rendimento da carcaça. Verificou-se aumento sobre a área de olho de lombo (AOL) e a espessura de gordura subcutânea (EGS), quando os animais não suplementados foram comparados com os suplementados. Não foi observado efeito para o comprimento da carcaça (CCA), nem para os rendimentos dos cortes comerciais. As exigências líquidas de energia e proteína apresentaram, respectivamente, aumento e redução com o aumento do PC dos animais. As exigências de energia líquida para mantença (ELm) foram de 85 kcal/PCVZ0,75. As exigências de energia metabolizável para mantença foram estimadas em 130,08 kcal/PCVZ0,75. A suplementação de bovinos no período de transição águas-seca aumenta o consumo de MS e energia, promovendo aumento do ganho de peso dos animais.

This experiment aimed to evaluate the performance, carcass characteristics, body composition, and energy and protein requirements of beef cattle under grazing conditions. The experimental area constituted of 5 paddocks with Brachiaria decumbens as forage source. Twenty two steers (Zebu) with mean body weight and ages of 320kg and 18 months, respectively, were used. Three animals were slaughtered at the beginning of the experiment and used as standard. Of the nineteen remaining animals, three were designated for maintenance group and the others were randomly submitted to one of four treatments: mineral mixture (MM), 1, 2 or 3kg of supplement daily. There was a linear increase in dry matter intake (DMI), digestible energy (DEI) and metabolizable energy (MEI), and total digestible nutrients intake (TDNI) was maximum consumption of 2.88kg of supplement. The maximum average daily gain (ADG), 0.91kg/day, was observed for supplement intake of 2.69kg/day. Linear increase was observed in shrunk body weight (SBW), EBW and carcass weight. There was no effect on the carcass allowance, however, it was observed on the ribeye area and back fat thickness. No effect was observed on carcass length and commercial cuts. The requirement of net energy (NE) and net protein (NP) increased and decreased as the animals BW increased. The maintenance requirement for net (NEm) and metabolizable energy were 85 kcal/EBW0.75 and 130 kcal/EBW0.75. Supplementation of cattle in the period of transition between rainy and dry seasons increased the dry matter and energy intake, promoting an increase in animal weight gain.