The effect of the spatial scale of heterogeneity of two herbage species on the grazing behaviour of lactating sheep

Abstract

The benefits of including clover in sheep pasture are well known, this study investigates a method to enhance these benefits by facilitating diet selection. Lactating ewes and their twin lambs grazed ryegrass (G; Lolium perenne cultivar ‘Parcour’) and white clover (C; Trifolium repens cultivar ‘Kent Wild White’) as either separate or conterminal (G:C) monocultures, or as mixtures (M), at a mean sward surface height (SSH) of 6.6 cm. There were two replicates of each treatment and there were four ewes and their lambs on each replicate. The grazing behaviour of the ewes was measured during an 8-day experimental period. For treatments M and G:C, clover content of the diet was estimated using an n-alkane technique. Ewes on treatments M and G:C selected higher proportions of clover (0.35 and 0.62) than was offered in the paddocks (0.09 and 0.43). The ewes on G:C made frequent transitions between the two herbage species and there was a significant linear increase in this frequency over the day ( P<0.001). The times spent eating were; G, 579 min per day; C, 495 min per day; M, 664 min per day and G:C, 592 min per day; P=0.072. Grazing times (eating times+intra-bout intervals ≤ 6 min) were; G, 673; C, 573; M, 706 and G:C, 640 min per day; P=0.062. Although not significant, the apparent longer eating time for ewes on M was reflected in the proportion of the day that the ewes spent standing (G, 0.50; C, 0.49; M, 0.58 and G:C, 0.52 of the day). The number of lying bouts per day was significantly higher on G than on the other treatments and significantly lower on M than on the other treatments (G, 32; C, 26; M, 18 and G:C, 24; P=0.001). The mean duration of these lying bouts was significantly less on G than it was on the other treatments (G, 23 min; C, 29 min; M, 34 min and G:C, 29 min; P=0.026). During eating the ewes on C and M appeared to walk more slowly than the other ewes. The ewes on G:C appeared to walk more quickly than the other ewes during eating and during intra-bout intervals, although none of these differences in speed were significant. The intake rates of the ewes were; G, 5.4 g DM min −1; C, 6.5 g DM min −1 and M, 4.2 g DM min −1; P=0.086. Daily intakes of the ewes were calculated (intake rate×eating time) as; G, 3126 g DM per day; C, 3233 g DM per day; M, 2797 g DM per day and G:C, 3569 g DM per day; P=0.119. During the experimental period the daily live weight gain of the lambs was significantly different between treatments (G, 17.2 g kg −1; C, 26.4 g kg −1; M, 14.3 g kg −1 and G:C, 19.8 g kg −1 live weight; P=0.002). So it appears there were benefits from offering grass and clover as separate monocultures and this may have been due to less time spent searching for clover.