Two experiments examined the effects of different defoliation treatments in spring on sward morphology and animal performance in mid-season and late season.

High (H; 27 350 m-=) or low (L: 13 300 m^^) tiller den.sily perennial ryegrass swards were created in the mid-and lale grazing season by imposing dlt'terenl sward heights in the spring. Summer-calving tows tben grazed these swards from 6 June to 2 September 1992 and were ottered 5 kg fresh weight hd^' d"' of either a barley (S) or a molassed sugar beet pulp (F) based supplement. The factorial combination of .sward and supplement types resulted in four experimental .swards being grazed by thirteen Holstein/Friesian cows each. Supplement F contained more crude fibre (110 vs. 58 g kg"') and less metabolizable energy [12 5 vs, 13>2 MJ kg"' dry matter {DM)] than supplement S, Herbage on the H sward contained more metaholizable energy (119 vs. 104 MJ kg"' DM) and crude protein (232 vs, 205 g kg"' DM), had fewer rejected areas (16'5 vs. 26-9%) and a higher live-^lead tiller ratio (4-6 vs. 21) than that on the L sward.Sward, but not supplement type, significantly affected the intake of grazed herbage (/'<00Ol), On average, the herbage intakes ot" cows grazing H swards were higher than for L swards (14-5 vs-116 kg DM d"') and those of cows on the S antj F supplements were 12-6 and 13-5 kg DM d^' respectively. Averaged over the grazing period, sward and supplement had no significant effects on milk yield, milk composition or yield of constituents. When expressed on an average weekly basis, cows grazing an L sward and offered the F supplement on occa-Currespondence: Dr G. E. J. Fisher, The Scottish Agncultural College. Auchincruive, Ayr KA6 5W. UK,

The objectives of Ihis experiment were to study the effects of different grazing managements in spring on herbage intake and performance of summer-

A perennial ryegrass sward was grazed by sheep in April 1993 to a target sward surface height (SSH) of 3 cm to create a high density of grass tillers. From 3 May, the sheep were removed and small plots were established on the sward, when the average tiller density (± s.e.) was 35 900 + 420 live tillers m~^. Different regrowth treatments were then imposed by allowing plots to regrow to target SSHs of 6 cm (18 g dry matter (DM) m'^), 9 cm (78 g DM m"^), 12 cm (132 g DM m'^) or 15 cm (197 g DM m'^). The plots were then maintained by cutting at either 6 or 9 cm SSH until the end of the experiment on 30 September. Live tiller density was reduced by regrowth beyond 8 9 cm (78 g DM m~^ P<0 001) and leaf-stem ratio and in vitro organic matter digestibility were reduced by regrowth beyond 6-1 cm (18 g DM m-2, P<005). The effect on live tiller density was sustained through the remainder of the season. From the beginning of June to the end of September, maintenance of SSH at an average of 9-1 cm compared with 6-4 cm also resulted in lower live tiller density, live-dead tiller ratio and leafstem ratio and higher herbage mass (at least P<005). There were significant interactions between regrowth SSH and maintenance SSH, so that leaf-stem ratio, live-dead tiller ratio and live tiller density were reduced by regrowth to a SSH of 16-4 cm followed by maintenance at 9-1 cm, com-

The U.K. Milk Marketing Boards are encouraging dairy farmers to produce more milk in the summer months. However, the management of May to July calving cows is difficult as peak yield and intake requirement coincide with declining grass growth and quality. One means of overcoming this problem has been to offer a forage buffer as an extra feed to supplement the intake of grazed grass. The objective of this experiment was to investigate optimising the performance of summer calving cows by manipulating grass sward morphology to improve grazing intakes and eliminate the need for a forage buffer.