Patrón de pastoreo y movimiento de vacas puras y cruza sobre campo natural bajo distintas ofertas de forraje durante la gestación media y tardía

In this work, the effect of forage supply (OF) and cow genetic group (GG) on grazing behavior, rumination behavior, and movement of pregnant multiparous beef cows grazing native pastures was studied. The measurements were made in autumn and winter of 2021, periods corresponding to the stage of middle gestation (114±26 days of gestation) and late gestation (205±26 days of gestation), respectively. This study was carried out in the Experimental Station "Prof. Bernardo Rossengurt" (EEBR - UdelaR), on an area of 49 ha, belonging to a long-term experiment, installed in 2007, where different levels of FA are studied, in breeding cows managed in a continuous grazing system of natural grasslands. The experimental design was an unreplicated factorial arrangement of FA and GG. In autumn, FA levels of 8 and 4 kg DM/kg LW were managed for high FA (HFA) and low OF (LFA), respectively, and in winter the OF in both treatments was 6 kg DM/kg LW. Two GG were evaluated in each OF treatment: Pure cows (PU), from Aberdeen Angus and Hereford breeds, and Cross F1 cows (CR), from reciprocal crosses between Aberdeen Angus and Hereford breeds. Once per season for each plot, the live weight and body condition of the cows were recorded and the forage structure variables were measured. Behavior and movement records were taken for 8 and 10 days, in April and July, respectively. 12 experimental cows were used in each sampling period, which were fitted with a RumiWatch muzzle to record grazing and rumination behavior patterns, and GPS equipment to take location records. In both periods, HFA presented higher forage mass and canopy height (2473 vs 1609 and 1939 vs 1653 kg DM/ha, respectively), while the percentage of area covered by high stratum was twice as high (17 vs 5 and 15 vs 6%, respectively). During mid-gestation, in HFA the grazing time (GT) (P˂0,01) and the bite rate (BR) (P˂0,01) decreased, while the explored area (EA) (P˂0,01) and the percentage of the plot explored (%EA) (P=0,02) increased. CR cows decreased BR (P˂0,01) and increased EA (P=0,02) and %EA (P=0,02), compared to PU. CR cows within AOF decreased GT (P=0,04) and BR (P˂0,01) and increased EA (P˂0,01), compared to LFA. In late gestation, HFA cows decreased BR (P˂0,01) and increased rumination time (RT) (P˂0,01) and EA (P˂0,01). CR cows in HFA decreased BR (P˂0,01). The behavior and exploration at the daily scale and during the grazing session of cows in medium and late gestation suggest that they modified the grazing strategy, associated with the canopy height and the percentage of area occupied by high stratum, which means that the forage is spatially patchy and, in these conditions, the cows decided to modify the harvest costs in terms of time or the rate of intake and rumination, integrating into the decision-making the difference in height between strata, the internal state of the animal and the body condition of the cow, which reflects plasticity in behavior to satisfy intake needs.