Abstract #M271

# M271
Effect of parity on grazing behavior of dairy cows grazing oat pastures.
J. P. Soutto1, P. Pellaton1, P. Gauthier1, M. Carriquiry1, P. Chilibroste*1, A. I. Trujillo1, 1Facultad de Agronomia, UDELAR, Montevideo, Uruguay.

Information concerning to grazing pattern of multiparous (MUL) and primiparous (PRIM) cows is especially valuable to understand mechanisms involved in feed intake as well as to improve dairy grazing management. The study was conducted in a randomized block design to assess the effect of parity (3 block; n = 9 cows per treatment) of Holstein dairy cows (days in milk = 73 ± 7; BW = 521 ± 32 kg; milk yield = 26 ± 3 kg) grazing a vegetative oat pasture (8 h of access to pasture from 8:30 to 16:30 h; pasture allowance = 30 kgDM/cow/day; DM = 14%, CP = 23%, NDF = 46%, dry basis) on grazing behavior (grazing, ruminating and idling times; GT, RT and IT, respectively) and number of prehension bites (NB). Cows were milked twice daily and fed, after the afternoon milking, 6 kg DM/day of a mixture (70:30 forage to concentrate ratio as-fed basis). Individual cows were observed every 5 min on 3 consecutive days and grazing, ruminating or idling and other activities were recorded. The GT, RT and IT were estimated assuming that the recorded activity was maintained between 2 consecutive records. The number of bites was estimated by counting prehension bites/min every 5 min during the grazing activity. All variables were calculated for the 8 h of access to pasture and for 4 intervals of 2 h each during the access time to pasture (INT1 to INT4). Data were analyzed as a repeated measures using a mixed model with treatment (MUL and PRIM), day and INT (when corresponded) as fixed effects and block as a random effect. The NB (14,990 vs 13,670; P = 0.033) and GT (320 vs 300 min; P = 0.075) were greater for MUL than PRIM while RT and IT did not differ (P > 0.10) between parities during access time to pasture. When INT were evaluated, differences were detected only in INT 3: MUL cows performed 591 more NB (P = 0.013) and grazed 14 min more (P = 0.012) than PRIM, while PRIM ruminated 7 min more (P = 0.048) and idled 7 min more (P = 0.0543) than MUL. Results suggest that the different grazing behavior performed by MUL and PRIM could be associated with different pasture intake.

Key Words: ruminant behavior, dairy cow, oat pasture