Desempenho e exigências de energia, proteína e minerais de bovinos de corte em pastejo, submetidos a diferentes estratégias de suplementação / Performance and energy, protein and minerals requirements of beef cattle at pasture, submitted to different supplementation strategies

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

This thesis was elaborated based upon four experiments that amaid to evaluate the effects of different supplementation strategies on performance and nutritional characteristics of beef cattle during dry, rainy and rainy/dry seasons at pastures of Brachiaria decumbens; as well as estimate the body composition and the energy, protein, calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K) and sodium (Na) requirements of beef cattle at pasture. In the Experiment 1 (Dry season), 25 zebu calves, with age and initial weights of 7.5 months old and 194. kg, respectively, were used for performance evaluation and five Holstein-Zebu steers fistulated in rumen and esophagus, with 290.0 kg of LW were used to evaluate nutritional characteristics. The different supplementation strategies evaluated were: self-feed supplementation (SF) and infrequent supplementation (1.0 kg/animal/day). The frequencies of supplementation evaluates were: three times/week (Monday, Wednesday and Friday 3X), five times/week (Monday to Friday 5X), six times/week (Monday to Saturday 6X) and daily (7X). There were no effects of different strategies (P>0.10) on intake expressed in kg/day or perceptual of LW. However, DM total apparent digestibility and crude protein ruminal apparent digestibility were higher in SF strategic. No differences (P>0.10) were observed on microbial N and DM flux and its efficiency. Serum and urine concentrations were higher in animals consuming SF strategic. In Experiment 2 (Rainny season), 25 steers with initial age and live weight (LW), respectively, 10.5 mouths old and 222.4 kg grazing in five paddocks of Brachiaria decumbens were used for evaluate the performance. The different supplementation strategies evaluated were: mineral supplementation (MIS), self-feed supplementation (SF) and infrequent supplementation (0.500 kg/animal). The frequencies of supplementation evaluates were: three times/week (Monday, Wednesday and Friday 3X), five times/week (Monday to Friday 5X) and daily (7X). Supplement dry matter (DM) intake on animals that receive SF supplementation was 0.523 g/day. The ADG and final LW was smaller (P<0.10) on animals that just fed MIS when compared to protein supplementation that didnt differ to each other (P>0.10). The ADG was 726.0; 891.0; 895.0; 885.0 and 892.0 g, respectively, for strategies MIS, SF, 3X, 5X and 7X. In experiment 3 (Rainny/dry season), 20 steers with initial age and live weight (LW), respectively, 14.0 mouths old and 311.0 kg grazing in four paddocks of Brachiaria decumbens were used for evaluate the performance. The different supplementation strategies evaluated were: mineral supplementation (MIS) self-feed supplementation (SF) and infrequent supplementation (0.550 kg/animal). The frequencies of supplementation evaluates were: three times/week (Monday, Wednesday and Friday 3X) and daily (7X). Supplement dry matter (DM) intake on animals that receive SF supplementation was 0.598 kg/day. The ADG and final LW was smaller (P<0.10) on animals that just fed MIS when compared to protein supplementation that didnt differ to each other (P>0.10). The ADG was 661.40; 812.7; 811.5 and 819.2 g, respectively, for strategies MIS, SF, 3X and 7X. Independent of strategy, the protein supplementation increased nutrients and pasture intake (P<0.10) expressed in kg/day and in % of LW, when compared with MIS. Pasture DM intake was 7.88 kg/day for MIS and 8.17 kg/day in animals that received protein supplementation. Animals that received SF protein presented higher crude protein intake (P<0.10). In relationship of digestibility, animals that fed protein supplementation presented higher CP, NDF and NFC total apparent digestibility and CP intestinal apparent digestibility. No differences (P>0.10) were observed between SF and infrequent supplementation, as well as for different frequencies of supplementation on total, ruminal and intestinal apparent digestibility. No differences (P>0.10) were observed on microbial nitrogen and DM flux and its efficiency. Less nitrogen balance was observed in animals feeding only MIS (P<0.10). In Experiment 4 a trial involving 27 zebu bulls at pasture with initial live weight (LW) of 311.0 kg were conducted with the objective of determining their energy, protein e minerals requirements. Three animals were slaughtered at the beginning of the trial, performing the reference group; four had grazing time restricted, to limit energy intake to a level close to the maintenance level. The remaining was uniformly allotted to a complete randomized design, in four treatments: mineral mix, self-feeding protein, protein supplementation three times per week (Monday, Tuesday and Friday) and daily. The relation between the empty body weight (EBW) and the live weight (LW) of these animals were used to estimate the initial EBW of the animals remaining in the experiment. The levels of fat, protein, energy and minerals (Ca, P, Na, K, Mg) retained in the body of the animals were evaluated using equations of logarithm regression of the body contents of protein, fat, energy, Ca, P, Na, K and Mg, related to EBW logarithm. The net energy requirement for maintenance (Nem) was estimated as the antilog of the intercept of the equation obtained by the linear regression between the logarithm of heat production (HP) and the metabolizable energy intake (MEI). The metabolizable energy efficiencies of utilization (MEEU) for maintenance (km) and weigh gain (kg) were estimated from the relationship between the net energy concentration, for maintenance or gain, respectively, and the metabolizable energy (ME) content of the diet. The amount of energy and fat in the gain increased as the body weight of the animals increased. The net energy requirements for gain (Neg) of zebu steers can be obtained by the equation: Neg = ER = 0,0617*BW0,75*EBG1,0564. The daily energy requirement for maintenance was 64,00 kcal/LW0.75. The estimated value for km was 0.64 and the calculated kg was 0.26. The protein requirements for gain decreased as the LW increased. The protein requirement found for an animal with 200 kg, was 153.71 g/kg EBW, while for an animal of 400 kg of live weight was 141.86 g/kg EBG. An equation was obtained to estimate the retained protein (RP) in function the live weight gain (LWG) and the retained energy (RE): RP = -34.6109 + 257.956*LWG 17.01*RE. Considering a steer with 400 kg of live weight, the estimated metabolizable requirements of protein for maintenance and gain were, 357.77 and 288.33 g/kg LW, respectively. The animals that were fed with protein supplementation presented large protein requirements than animals not supplemented, due the largest intake of total digestible nutrients (TDN). An animal with 400 kg of LW fed protein supplementation, the daily protein requirements in terms of degradable and no degradable protein were, respectively, 764.22 and 73.89 g. The requirement of crude protein was 838.10 g/day. There was a decrease in the empty body and in the gain of empty body concentrations of the five macrominerals studied, with the elevation of the live weight. The relationships g Ca/100g of retained protein and g P/100g of retained protein were 10.92 and 5.26, respectively. Total dietary requirements of calcium was smaller than recommended by (NRC, 2000), however the one of phosphorus was close.

ASSUNTO(S)

suplementação alimentar beef cattle proteína pasto feed supplementation nutricao e alimentacao animal protein bovino de corte minerals energy minerais energia pasture

ACESSO AO ARTIGO

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