The responses to supplements differing in protein concentration and degradability were measured in lactating ewes and their twin lambs when offered fresh ryegrass either cut or grazed. Housed Scottish Halfbred ewes, offered fresh-cut grass ad libitum received no supplement (N) or supplements with barley and maize starch (B); barley and soya-bean meal (S); barley, soya-bean meal and fish meal (SF) or barley and fish meal (F) in weeks 2 to 7 of lactation. By feeding supplements, herbage organic-matter (OM) intake was depressed (2·00 v. 1·74 kg/day). Mean daily milk yield was increased when protein supplements were given and, because milk protein concentration was higher for supplement F and similar for all other diets, mean daily milk protein output increased with increasing fish meal in the diet. Milk yields were N 2·55, B 2·59, S 3·17, SF 3·15 and F 3·17 kg/day. Total milk solids and fat concentrations were also higher for S, SF and F than N or B. Lambs from ewes supplemented with protein grew faster and the ewes generally lost less weight and body condition compared with unsupplemented ewes.
At pasture, Masham ewes grazed at herbage allowances of either 4 (L) or 10 (H) kg OM per day and received no supplement (N) or supplements B or F, for the first 6 weeks of lactation and then, in weeks 7 to 12, grazed without supplements. For NL, BL, FL, NH, BH and FH respectively lamb growth rates from birth to 6 weeks were 235, 242, 274, 267, 286 and 302 g/day; from birth to 12 weeks were 210, 209, 249, 255, 275 and 287 g/day and losses in ewe body-condition score from birth to 12 weeks were 1·28, 1·22, 1·06, 0·97, 0·62 and 0·76.
It is concluded that protein supplements increased milk yield and lamb growth rates and that the response tended to be greater with fish meal.