Temporal foraging strategy of lactating beef cows grazing native subtropical grassland differing in herbage allowance...

We study the effect of herbage allowance (HA, High HA vs. Low HA, 5 vs. 3 kg DM/kg BW respectively) on temporal foraging strategy during lactation (40±12 d after calving) in two years using 34 cows equipped with automatic behavior recorders during herbage intake assessment. Herbage mass (HM), and its chemical composition were assessed, while daily grazing (GT, min/d) and ruminating time (RT min/d) were monitored and expressed relative to herbage intake (DMI) in kg/cow/day. The number of feeding stations (FeSt) per minute and bites/FeSt were recorded by direct observation for 30 min/d in two to four cows per plot for two or three consecutive days. Data analysis using MIXED model with HA as fixed and block as random effect was performed using the plot as the experimental unit. Cows in High HA increased the DMI by 1.3 and 3.7 kg/cow/d in years one and two respectively and the greater DMI could be partially explained by access to greater HM in both years and by grazing behavior at FeSt. Cows in the High HA group showed a tendency toward more selective foraging behavior, with an increase in FeSt/min (P = 0.09) and a decrease in bites/FeSt (9 vs. 13 ± 2; P = 0.08), suggesting enhanced selectivity despite marginal statistical significance but when integrated over 11 h of GT it significantly affects DMI. In the second year, RT/kg DMI tended to increase in the Low HA group, competing directly with GT. This suggests that lower DMI could trigger a behavioral adaptation to increase digesta retention time diminishing particle size through rumination trying to extract more nutrients of the herbage ingested and making space for new herbage intake.