Suplementação com ionóforo à dieta de novilhas leiteiras em crescimento compensatório / Ionophore supplementation in the diet of dairy heifers in compensatory growth

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The objective proposed for this study was to evaluate the compensatory growth regimes and the supplementation with ionophores to the diet on the performance, digestive parameters, metabolic profile and mammary gland development of dairy heifers. The experiment was carried out during the period of April to September of 2004. Twenty purebred heifers from the Brown-Swiss breed were used, with average of initial weight of 200 kg and five months old. The treatments were arranged in a factorial arrangement (2x2x2) and the animals were randomly allocated in each one of the combinations. The factor 1 consisted of the feeding regime (conventional and compensatory growth), the factor 2, of the use or not of ionophores (200 mg of monensin/animal/day) and the factor 3, of the feeding periods. The animals in the conventional regime received ad libitum feeding, while the one in the compensatory growth regime were submitted to a nutritional management with two different periods: period of energy restriction (90 days, P1) and realimentation period (60 days, P2). A smaller efficiency of conversion of dry matter and energy metabolizable consumed in average daily gain was observed, during the realimentation period. There was no difference for the variables related to the nitrogen balance of the animals of the conventional regime and of the submitted to the compensatory growth regime. The ionophores inclusion in the diet of the heifers provided smaller excretion of urinary nitrogen (N) and, consequently, larger N retention in the period of restriction and smaller in the realimentation period, which reflected in the efficiency of use of consumed N. There was not effect of the treatments, of the ionophores use or of the period on the studied morfo-structural parameters and on the final body weight. Heifers in compensatory growth regime showed larger average daily gain at the 1350 and 1500 days of the experimental period in comparison with the ones from the conventional regime. The ionophores inclusion in the diet increased the coefficients of total digestibilities of the dry matter, of the organic matter, of the total carbohydrates and of the neutral detergent fiber. There was no effect of the treatment, of the ionophores addition to the diet and of the period on the microbial production. The microbial efficiency (g microbial CP /kg of TDN consumed) in the restriction period was larger than in the realimentation period. The animals from the compensatory growth regime showed smaller daily time spent in feeding and total mastication, but they did not differ from the animals from the conventional regime as for the time spent with rumination. Heifers submitted to the compensatory growth regime showed larger concentration of plasma ureic nitrogen (ureic N) and smaller DNA: RNA ratio in the mammary gland. When analyzed inside of period, the levels of high density lipoprotein (HDL) increased in the realimentation period, while the ureic N decreased. Besides the alteration in the levels of ureic N, the energy balance to which the heifers in compensatory growth was submitted caused increase in the content of the noesterified fatty acids (NEFA). There was reduction in the blood glucose levels of the animals in compensatory growth in the realimentation period. Among the variables of metabolic profile studied, the supplementation with ionophores to the diet showed effect only on NEFA, that had it concentration reduced during the realimentation period. Based on the obtained results, it could be inferred that the nutritional regime for compensatory growth in dairy heifers and the supplementation with sodium monensin to the diet had positive effect on the digestibility of the nutrients and metabolic profile, originating, finally, increase of the activity of protein synthesis in the mammary gland. But, its should be considered that the compensatory growth regime not always promotes increase in the efficiency of conversion of the dry matter and of the energy metabolizable consumed in average daily gain and, consequently, increase in the nitrogen balance of the animals. On the other hand, the ionophores inclusion in the heifers diet reduces the excretion of urinary N, providing larger retention of N.

ASSUNTO(S)

feeding behavior bovino leiteiro digestibilidade food restriction digestibility restrição alimentar dairy cattle comportamento ingestivo nutricao e alimentacao animal

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