Effect of breed and sward height on sheep performance and production per hectare during the spring and autumn in Northern Spain

Effects of breed and sward surface height on ewe liveweight and body condition changes and on lamb liveweight gains during grazing in the spring and autumn were studied. The output per hectare in each season was also calculated. A total of 112 Gallega ewes (35Æ6 kg live weight) and 204 Latxa ewes (47Æ5 kg live weight) with their lambs were used during the spring (March–June) to study the effect of five target sward heights (3Æ0, 4Æ5, 5Æ5, 6Æ5 and 8Æ0 cm) and the interaction with breed. In autumn (October–December) 155 Gallega and 126 Latxa ewes were used to study the effect of three target sward heights (4Æ0, 5Æ5 and 7Æ0 cm) and the interaction with breed. Each study was replicated twice. A quadratic relationship was found between sward height and ewe liveweight and body condition changes and lamb liveweight gain during the spring grazing season, with the maximum individual performance being achieved at around a sward height of 6Æ0 cm. There were significant breed · sward height treatment interactions for ewe liveweight and body condition changes, and lamb liveweight gains. Higher liveweight gains were achieved by Latxa ewes and lambs in swards taller than 6Æ5 cm but they also sustained higher liveweight losses in swards shorter than 4Æ5 cm. Nevertheless, a higher output (liveweight gains of ewes + lambs) per hectare for a given weaning date or age was achieved by the Gallega ewes. In autumn, the relationship between liveweight change and sward height was linear, with a breed–sward height interaction similar to that observed in the spring. Sward surface heights of 4Æ0–4Æ5 cm and 4Æ5–5Æ0 cm were required to maintain live weight and body condition in spring and autumn respectively. Lamb and ewe liveweight gains per hectare decreased considerably in swards taller than 6Æ5 cm.