Estudio de la selectividad de estratos y comportamiento a nivel de estación de alimentación en vacas pura y cruza a diferentes ofertas de forraje en pastoreo de campo natural

During the autumn-winter period of 2021, the ingestive behavior of multiparous gestating beef cows was studied at the level of feeding station, diet selection at bite level and energy intake to determine the effect of forage allowance (FA) and cow genotype (G) on these variables. The experiment was carried out on 49 has of native grassland, that has been maintained at continuous stocking since 2007, belonging to the “Prof. Bernardo Rosengurtt” Experimental Station (EEBR). The experimental design was a non-replicated factorial arrangement of FA and G. The FA was 8 kgDM/kgLW and 4 kgDM/kgLW in autumn for High FA (HFA) and Low FA (LFA) respectively, while in winter it was 6 kgDM/kgLW for both FAs. The Gs were Pure (PU, Hereford and Aberdeen Angus) and cross (CR, F1 reciprocal crosses). The registers of the ingestive behavior were made in April and June, videorecording for 40 minutes in the morning, and same time in the afternoon, for two consecutive days in 3 animals per plot (experimental units). The energy intake was estimated through energy requirements (NRC, 2007), utilizing live weight, evolution of condition score, birth weight and days of gestation as enter variables. Animals responded to the changes in sward structure imposed by the changes in OF, changing their ingestive behavior. Higher FA caused a reduction in the number of feeding stations per minute (FS/min) (6,22 vs 7,66 HFA vs LFA), while the number of steps per FS (S/FS) (1,62 vs 1,49 HFA vs LFA), bites per FS (B/FS) (7,92 vs 7,09 HFA vs LFA) and the percentage of bites made in the upper stratum of the sward (6,98 vs 2,38 HFA vs LFA) were higher in HFA than in LFA. The use of CR animals increased the number of FS/min (7,59 vs 6,29 CR vs PU) and diminished the number of B/FS (6,75 vs 8,27 CR vs PU). Energy intake (12,4 vs 12,1 McalEN/d HFA vs LFA) and condition score (5,2 vs 5,5 HFA vs LFA) were not affected by FA, but energy intake (11,1 vs 13,5 MalEN/d CR vs PU) was affected by G. Energy intake showed a quadratic response to the FS/min number. The information obtained in this work helps us to advance in the knowledge about how changes on the sward structure affect ingestive behavior. Furthermore, we were able to determine that the FS behavior affects energy intake and that this variable is negatively affected by increasing amounts of sward area covered by the high stratum. In addition, it was determined that there are no productive advantages of working with levels of FA similar to those of HFA during mid-late gestation. However, this increase in FA allows a greater forage mass accumulation, which can act as insurance against droughts or other factors that reduce the forage accumulation rate.