Resumen de Growth of heifers grazing on dry season and limited access to Leucaena leucocephala, molasses / urea and / or concentrate
Rafael Mejías, Paul F. Randel, Ernesto O. Riquelme Villagran
During five 35-days periods of progressive drought, 24 heifers of 278 kg mean initial liveweight (LW), in four equal groups, grazed with weekly rotation in three paddocks (6.59 ha total) of unfertilized heterogeneous grasses (G). In periods 1 and 2, four treatments (2 x 2 factorial) were based on the factors (a) access for 3 hours daily to rotational grazing in three paddocks (2.57 ha) of leucaena in association with grasses (GL) and (b) 2.5 kg per head daily of cane molasses with 3% urea (MU). Mean daily LW gain in 70 days was .18 kg in the control (I). of G supplemented with minerals only; by addition of MU (II), GL (III}, and of both MU and GL (IV), rate of gain was increased to .30, .35 and .38 kg, respectively. In period 3, it was modified by addition of 2 kg per head daüy of concéntrate feed, even so LW change was -.02 kg daily; also in II there was a daily loss of .34 kg, contrary to gains of .32 and .66 kg in III and IV, the latter surpassing (P< .10) T-1 and T-2. In periods 4 and 5, addition of 4 and 2 kg daily of concentrates in I and II resulted in gains of .78 and .63 kg, while in III and IV the daily rate slowed to .26 and .30 kg. Over 175 days, III and IV (GL without concentrates) resulted in daily gains of .31 and .40 kg vs. .38 and .30 kg for I and II (G with concentrates}. Treatments differed little in growth of heart girth; LW increased 4.7 kg per cm increase therein. Among periods crude protein content in G and GL ranged from 8.9 to 12.3% and 14.9 to 1 8.0%; and ¡n vitro digestibility from 73.8 to 78.3% and 72.7 to 77.4%, respectively. Limited supply of forage G, rather than deficient nutrient composition, was the main factor limiting animal performances; GL corrected this storage more efficiently than MU.
