Abstract #T175

# T175
Effect of stocking rate at system level on produced and harvested forage.
G. Ortega1, Y. Lopez1, T. Nuñez1, D. Custodio1, R. Mello1, P. Chilibroste*2, 1Agronomy Faculty, Animal Science Department CRS, Progreso, Canelones, Uruguay, 2Agronomy Faculty, Animal Science Department, Grass Production and Utilization on Grazing Systems, EEMAC, Paysandú, Paysandú, Uruguay.

A farmlet study was being conducted to determine the effect of stocking rate on feeding strategies and individual milk production of autumn calving grazing dairy cows. Four farmlets (2 per treatment) representing a pasture based dairy system in Uruguay, which combines annual with perennial pastures under a 4-yr rotation, were grazed either with 1.5 (MSR) or 2.0 (HSR) milking cows per hectare from June to December 2016. Ninety-six cows were randomized to the farmlets based on parity (3.3+ 1.3), BW (500 ± 91) and BCS (2.95 ± 0.87). Every week, the sward mass of each individual plot in each farmlet was assessed through the double sample technique (Haydock and Shaw, 1975). Based on these observations, mean growth rate (GR, kgDM/ha/day) for each paddock and the whole farmlet was estimated. The grazing area was adjusted weekly based on the GR registered for each treatment. Cows grazed a daily strip with a mean herbage allowance of 15.4 and 13.4 kgDM/d over 6 cm for MSR and HSR, respectively. Before and after grazing, mean sward height and the phenologic stage of the pastures were registered in each individual grazing session.The data were analyzed with a mixed model that included stocking rate and month as fixed effects and farmlet as a random effect. The repeated measurement was week, and an autoregressive covariance structure (order 1) was selected. Differences were declared significant when P < 0.05. Cows on HSR grazed a larger amount of grass (825.3 vs 517.2kgDM/month/ha) than MSR. Sward mass (1772 vs 1750 kg DM/ha) and GR (50.2 vs 53.2 kg DM/ha/day) did not differ significantly between treatments. Accumulated grass harvested was 4761 kgDM/ha for MSR (76% grazing: 24% haylage) and 5777 kgDM/ha for HSR (100% grazing). Accumulated milk production per hectare was different (7654 vs 10760 L for MSR and HSR, respectively). We concluded that when good grazing management practices are applied, increasing stocking rate will not affect mean stock of pasture or growth rate. However, according to stocking rate, the ratio between direct (grazing) and mechanical (mowing) harvesting will be affected.

Key Words: stocking rate, growth rate, milking cows