Effect of restricted time at pasture and indoor supplementation on ingestive behaviour, dry matter intake and weight gain of growing lambs

Herbage intake and production performance of animals are likely to vary between different levels of time grazing pasture because of related changes in foraging behaviour. The effect of restricting pasture access on ingesting behaviour and performance of growing lambs is poorly understood. Thirty-two castrated male Ujumuqin lambs were randomly assigned to the following four treatments: (i) 2-h access to pasture (2H), (ii) 4-h access to pasture (4H), (iii) 8-h access to pasture (8H), and (iv) 12-h access to pasture (12H; control). The lambs began to access pasture at 6:00 h and were removed at 8:00 h, 10:00 h, 14:00 h and 18:00 h for 2H, 4H, 8H and 12H treatments, respectively. All lambs off the pasture were housed and separately fed supplements of concentrate and grass hay. The results showed that ingestive behaviour of lambs was significantly affected by restricting access to pasture. When time at pasture reduced from 12 to 2 h, the proportion of time grazing pasture increased (P<0.001), as did the pasture intake rate (P<0.001), but the proportion of time resting and standing and walking distance decreased (P<0.001). Significant linear relationship was found between supplement and pasture intakes. On average, total feed intake and metabolisable energy intake were unaffected by restricting pasture access, but in July weight gain of lambs clearly increased with less time at pasture. Grazing lambs with supplementation have a good ability to adapt to the restricted grazing schedules through varying their ingestive behaviour. Overall, the results indicate shorter grazing times and higher supplementation in July, with longer grazing times and lower supplementation through August and September is the most efficient to maintain higher lamb growth rates.