La utilizacion de raigras (Lolium multiflorum cv. Jack) en la alimentacion de terneros: Efecto de la oferta de forraje sobre el crecimiento, comportamiento animal y utilizacion de la pstura

The objective of the work was to evaluate the effect of grazing intensity, which was regulated through the forage supply (kg dry matter/100 kg live weight), of a ryegrass pasture (Lolium multiflorum cv. Jack) on the average gain of calves during autumn winter, forage utilization efficiency, dry matter consumption, pasture quality, and animal behavior. The experiment was carried out in the Intensive Meat Production Unit (UPIC) located at the “Dr. Mario Alberto Cassinoni” (EEMAC) Faculty of Agronomy, Paysandú; Uruguay between May 20 and September 3, 2022, totalling 106 days. Thirty-six Hereford calves, born in the spring of 2021, belonging to the EEMAC breeding herd, with an average live weight of 132.18 ± 9 kg were used. They were drawn into 12 groups (after stratification by live weight) and these randomly assigned to the different treatments defined by increasing levels of forage supply (OF): 2.5; 5.0; 7.5; 10.0; kg MS/100 kg live weight, respectively. Each treatment was composed of 3 repetitions made up of 3 calves grazing an independent plot. Rotational grazing was carried out in plots with 7 days of occupation, returning to it depending on the accumulated biomass. During the experimental period, no significant effect of the treatment was detected (P>0.05) on the availability and pre-grazing height, or the chemical composition of the forage offered (P>0.05). The remnant and the height associated with it showed a linear response (P<0.01) with the maximum remaining forage and its height found in the OF 10%. Utilization presented a negative quadratic response, with the lowest utilization value observed in the OF of 9.5%. The average daily live weight gain increased linearly with OF (P<0.001), associated with a significant increase in dry matter consumption (P<0.001) and increases in the concentration of protein in the diet, the latter evidenced by a greater opportunity for selection by increasing the supply of forage. However, no significant differences were found with changes in OF in grazing, rumination or rest activity (P>0.05) or in bite rate.