Resumen

DEPABLOS, Luis; ORDONEZ, Jorge; GODOY, Susmira  y  CHICCO, Claudio F. Mineral proteic supplementation of grazing beef heifers in the central plains of Venezuela. Zootecnia Trop. [online]. 2009, vol.27, n.3, pp.249-262. ISSN 0798-7269.

During the transition rainy-dry and dry season in a dry tropical forest, 166 beef heifers with 636 ± 2.46 days old and 219.62 ± 15.68 kg average body weight (BW) were assigned by BW, uterine conditions, ovarian structure, and racial predominance to three experimental treatments (S = common salt, SM = complete mineral supplement with 13.6% of P and 24% Ca, and SMP = protein plus mineral supplement with 42.5% PC and 0.58% P) 139 days before matting and 103 in matting. S and SM were given ad libitum and SMP about 700 g/animal/d. Body weight changes, body condition scores (BCS), reproductive tract evolutions, and pregnancy rate were evaluated. In addition, in blood serum, concentration of minerals, urea and non esterified fatty acids (AGNE) were measured. The animals were rotated in 122 ha divided in six paddocks of Cynodon sp. and Brachiaria sp. fertilized previously with urea (50 kg/ha). The evaluation of the offer of forages showed concentrations of nutrients and dry matter (> 34 kg DM/AU/d) adequate for beef cattle production. SM and SMP supplementations had no significant effect on BW or BCS of the animals. Nevertheless, considering the season of the year when the experiment was conducted, the average growth rate (0.483 kg/animal/d) was adequate for the general management of the herd, mainly in relation to pasture management. No significant differences among treatments were found for blood chemistry, uterine evolution, ovarian structure, and pregnancy (84, 84.1 and 92% of pregnancy for S, SM, and SMP, respectively). Under the experimental conditions, the mineral or protein plus mineral supplementations did not improve the biological response of the animals. Only rational management of pasture provides adequate vegetal material in quality and quantity, and consequently, satisfactory nutrition.

Palabras clave : supplementation; heifers; protein; minerals; reproduction.

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