47 Effect of two herbage allowance on herbage mass, stocking rate and cow body weight and condition score.

Abstract Beef cow-calf systems grazing native grasslands need to increase the animal production and economic sustainability, increasing production/ha, where stocking rate and individual performance are key issues. Previous research showed greater animal productivity per cow and ha when herbage allowance (HA) was increased from 3 to 5 kg DM/kg BW annual mean. The objective was to quantify the effect of two HA, High and Low (mean 5 vs. 8 kg DM/kg BW, but variable between seasons, 12, 8, 8, 4 and 8, 4, 4, 4 for High and Low HA during spring, summer, fall and winter respectively) for three cow cycles on herbage mass (HM), stocking rate (SR), and cow BW and BCS. Experiment was carried out in two blocks (52 and 61 ha) each with four paddocks. Multiparous beef cows diagnosed pregnant each year (58, 42, and 55 cows in years one to three) were allocated to one of each treatment. Data of HM, SR and actual HA was analyzed using mixed models from SAS with the plot as the experimental unit and the block as the random effect, while for animal variables the cow was used as the subject of the model, initial BW and BCS were used as covariables, covariance structure AR1 and the cycle was separated by 30 days and block was the random effect. High HA increased (P < 0.05) the HM in all cows cycles (2466 vs 1616±220, 2673 vs 1564±255 and 2306 vs 1212±234 for High and Low HA during the three cycles) however, stocking rate was without effect of HA during the first cycle (443 vs 410±19 High and Low respectively) a tendency (P=0.09) to increase the stocking rate in Low HA (505 vs 562±65, High and Low) in the second and greater (P < 0.01) stocking rate in High HA (378 vs 334±23 High and Low HA) in the third cycle. Cows mean BCS did not differ between HA in years 1 and 3 but was greater (P < 0.01) in High HA in year 2 (4.36 vs 4.10±0.07), while cow BW follow the same pattern with differences (P < 0.01) in year 2 only (472 vs 453±4.5 kg, High and Low respectively). The results highlight that there was an advantage for High HA in HM, without a clear disadvantage in stocking rate, and the greater HM should allow the greater BW and BCS of cows during the year two. The preliminary results showed that HA of 8 kg/kg BW should be recommended for managers, which in a context of high climate variability should increase the resilience of the grazing systems.