La Utilización de raigrás (Lolium multiflorum cv. Bill Max) en la alimentación de terneros: efecto de la oferta de forraje sobre el consumo, la selección y el comportamiento

The objective of this work was to evaluate the effect of grazing intensity, which was regulated through the supply of forage (kg dry matter / 100 kg live weight), from a ryegrass pasture (Lolium multiflorum cv. Bill Max) on dry matter intake, forage utilization efficiency, pasture quality and animal behavior and in this way, generate technical coefficients that are useful when planning and making decisions. The experiment was carried out in paddock number six of the Intensive Meat Production Unit of the Experimental Station of the Faculty of Agronomy “Dr. Mario A. Cassinoni” (EEMAC), located in the department of Paysandú, Uruguay. The experimental period was developed during 106 days between May 20 and September 3, 2022. For the experiment, 48 calves of the Hereford breed, born in the spring of 2021, belonging to the EEMAC experimental herd, were used. The animals started the experiment with an average live weight of 121 ± 31 kg, they were sorted into 12 groups (previous stratification by live weight) and these were sorted to the different treatments defined by the forage supply, which were 2,5; 5,0; 7,5; 10,0; kg DM/100 kg of animal LW, respectively. Accordingly, each treatment consisted of 3 repetitions made up of 4 calves grazing an independent plot. Rotational grazing was carried out on the plot for 7 days of occupation, returning to it based on the accumulated biomass. During the experimental period, no significant effect of the treatment (P>0.05) on availability and pre-grazing height was detected. The rejection and the height associated with it showed a quadratic response, where as the forage allocation increased, decreasing increases were recorded, finding the maximum remaining forage and its height, in the 10 % allocation. Utilization presented a negative quadratic response, with the lowest utilization value being observed in the 10% allocation. On the other hand, the consumption of the animals was always higher in the treatment with the highest allocation (10%), in relation to the most restrictive allocation (2.5%). Said consumption presented a quadratic response, so much so that going from an allocation of 2.5% to 5% represented an increase of 51%, while going from the allocation of 7.5% to 10% this increased by only 23 %. Forage allocation did not affect the chemical composition of the offered pasture (P>0.05), but it did improve the crude protein concentration of the selected diet; Based on this, the real consumption of crude protein was higher than that presented by the pasture, evidencing selectivity. No significant differences were found in the grazing activity compared to changes in forage allocation (P>0.05). Regarding rumination and rest, significant differences were detected for the treatment effect (P<0.01). Lastly, there was an effect of the treatment (P<0.05) on the bite rate, which presented a quadratic response that is maximized in FA 7.5%.