Grazing methods and herbage allowances effects on animal performances in natural grassland grazed during winter and spring with early pregnant ewes

The experiment was carried out in an 8.4ha natural grassland area, subdivided into 12 experimental units, each one of 0.7ha for 196 consecutive days, divided into seven 28-day periods. During the first 84 days (winter, periods 1–3), pregnant ewes were submitted to two grazing methods (continuous and rotational stocking; CS and RS) and two herbage allowances (HA; 12 and 18kg DM/100kg live weight (LW)), resulting in four treatments: C18, C12, R18 and R12. From day 85 on (pregnancy final third), all paddocks were managed with C18 to avoid food restrictions. It was measured on pasture:herbage mass (HM), net herbage accumulation, green leaf mass (GLM); and on animals:ewe body condition score (BCS), daily weight gain (DWG), lambs birth weight and animal production per area (ewes, lambs and total LWG/ha). During the first 84 days, HM was similar in the treatments and differed over the periods. After day 85, the HM was higher in RS and in 18% HA treatments. The changes in the HM cause modifications in the GLM. From period 1 to 3, ewes DWG was affected only by the HA treatment. In the 18% HA, pregnant ewes presented a positive weight gain, and in the 12% HA treatment the ewes lost weight. The grazing methods and HA did not have significant effect on the lamb birth weight. The grazing methods and the HA did not have significant effect in the DWG of the ewes but, in spring, the RS method promoted, on average, 7.3kg/ha less ewe weight than CS. The DWG from the lambs was not affected by the treatments. Areas managed with C12 treatment in winter presented superior lambs LWG/ha than areas managed with R18. The R18, R12 and C18 were similar. The C12 treatment improved the TLWG/ha, compared to the R18 treatment, but it was similar to C18 and R12. Variations in grazing methods combined with HA in the beginning of pregnancy did not affect lambs weight at birth. High stocking rate in winter in a continuous stocking was shown to have the highest productivity.