EFFECT OF A BANK OF Centrosema macrocarpum ON THE GROWING PHASE OF DAIRY HEIFERS GRASSING Digitaria swazilandensis GUALACA, PANAMA.

Abstract

The effect of a bank of Centrosema macrocarpum on the growing phase of dairy heifers grassing Digitaria swazilandensis was evaluated. Two treatments were evaluated (TR): grassing on Swazi (TS) and grazing on Swazi plus a restricted access to a protein bank (TSB). Seven heifers per treatment were utilized with an initial weight of 114.6 kg (±22.0), and 8.9 months of age. The grass was fertilized and managed rotationally under a grassing pressure of 2.0 UA/ha. The bank was constituted by cultivars CIAT 5062 and CIAT 5434 of Centrosema macrocarpum, which were managed under a daily and rotational grassing each other two hours, fertilized and supporting 10 UA/ha. The biomass availability (BA) of the grass each grassing cycle was 50% lower during the dry season (1198 kg/ha) than in the raining season (2381 kg/ha), but with a low difference between treatments. Crude protein and the in vitro digestibility of dry mater (IVDDM) for this grass showed a similar pattern when compared to the BA, with means of 8.64 and 4.53%, and 57.6 and 39.6% for rainy and dry seasons, respectively. Regarding to the legume, the mean of BA for the rainy and dry season were 2705 and 1663 kg/ha, with a grassing pressure of 2.20 and 1.42 kg of DM/100kg of BW per day, respectively. The proportion leaf/stem for the legume did not vary too much throughout the year (0.92), as well as for the CP and the IVDDM, with means for leaves and stems of 19.65 and 8.11% and 54.75 and 48.22, respectively. The interaction TR*EA for the weight gain (WG) was significant (P<0.02). There was not effect of treatment over the WG during the rainy season (P>0.21), but TSB increased during the dry period (P<0.06), with means of 0.076 and 0.280 kg/animal/day for TS and TSB, respectively. Both treatments showed the higher WG during the rainy season (P<0.001), with means of 0.641 and 0.178 kg/animal/day during the rainy and dry season, respectively. In conclusion, the C. macrocarpum bank increased the WG of the heifers just during the dry season, where the grass had low levels of CP.