Short-Term Herbage Intake of Grazing Multiparous and Primiparous Holstein Cows

Differences in the grazing harvest process between multiparous (MUL) and primiparous (PRIM) dairy cows could be explained by short-term grazing behavior (i.e. instantaneous herbage intake rate, bite mass, length of the grazing bouts). Therefore, this study was conducted in a randomized block design (3 blocks; n = 9 cows per parity) to assess the effect of parity on herbage intake (HI), HI rate, length of grazing bout, bite rate, and bite mass during the first grazing bout in the am grazing session. Cows (days in milk=73±7 d; BW=521±32 kg; BCS=2.75±0.25; milk yield=26±3 kg) grazed a vegetative oat pasture (8 h of access to pasture from 8:30 to 16:30 h; pasture allowance = 30 kg DM/d; DM=14%, CP=23%, NDF=46%, DM basis) and were individually fed 6 kg DM/d of a mixture (70:30 forage to concentrate ratio, as-fed basis) after pm milking. Herbage intake was estimated by weighing animals before and after grazing with correction for insensible weight loss (2 consecutive d). The HI rate (kg DM/min) was estimated by dividing HI by the length of the grazing bout, bite rate (bite/min) by counting prehension bites during 1 min every 2 min and the bite mass (g DM/bite) by dividing HI by the number of bites. Data were analyzed using a mixed model with parity as fixed effect and block as a random effect. Cow HI (5.6 vs. 4.5 ± 0.35 kg DM/d; P= 0.043 and 0.096 vs. 0.087 ± 0.005 kg DM/kg BW; P= 0.088), HI rate (0.051 vs. 0.043 ± 0.003 kg DM/min; P= 0.008) and bite mass (0.98 vs. 0.79 ± 0.07 g DM; P= 0. 013) were greater for MUL than PRIM while bite rate and the length of the grazing bout did not differ (P>0.10) between parities. Results indicate that bite mass plays a central role in the short-term intake behavior when MUL and PRIM dairy cows were compared. Differences in bite mass could be explained by grazing adaptability, hierarchical relationships or physical factors (i.e. mouth dimension).