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Supplementation and cattle breed effects on utilization of deferred tropical pastures

Roxana Avila ; Carlos Ferrando ; Damian Torres
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In deferred C4 pastures, supplementation is generalized practice for increasing animal live weight gains. Supplementation and animal factors can affect pasture use by increasing or decreasing the amount of grazed forage. The aim of this study was to evaluate the effect of supplementation on the utilization rate of a deferred C4 low-quality pasture when grazed by two cattle breeds (B) in the arid Chaco region, Argentinean. Thirty two heifers (body weight= 152?12 kg, age= 194?17 d old) were used in a 152-d trial, and were arranged in a 2x2 factorial randomized design. Tested factors were: supplementation (S, 2 levels), supplemented (WS) and no supplemented (NS); and Breed (B, 2 levels), Aberdeen Angus (AA) and Criollo Argentino (CA). Two replications per treatment were assigned to 8 Cenchrus cilliaris paddocks (3.25 ha and 4 animals each one). WS animals received a protein-energy ration (3.12 McalME kgDM-1 and 14% CP) at a day rate of 0.8% of BW. Forage availability (FA, kgDM ha-1) was determined in each paddock approximately every 28-d. Double sampling method consisting on 50 estimations and 10 clipping (frame=0.5 m2) along a 500 m transect was used for FA determinations. Forage utilization rate (FUR, kgDM d-1) was determined by linear regression considering FA (kgDM ha-1) as dependent variable and time (d) as independent variable, and for treatment comparisons (p<=0.05), dummy variables were included (y= ?0+?1x+?2D1+?3D2+?4D3+?5D1*x+?6D2*x+?7D3* x+?). Initial FA was 2927?317. FUR difference between breeds was detected (p=0.0021) in NS (NSAA=13.64 vs NSCA=8.93) but not (p=0.7376) in WS (WSAA=10.45 vs WSCA=9.96). FUR was different (p=0.0325) between NS and WS in AA (NSAA=13.64 vs WSAA=10.45) but was not (p=0.4843) in CA (NSCA=9.96 vs WSCA=8.93). Results suggest that, within the limits of this study (types and levels of evaluated factors), supplementation and cattle breed would be factors affecting forage utilization on deferred C4 pastures.