Whilst it is predicted that for finishing cattle (over 350 kg at start) fed grass silage diets, rumen degradable protein (RDP) should provide all protein requirements, previous studies have shown very variable growth responses from protein supplementation of cereal or starchy concentrates fed with grass silage. The protein source usually used being white fish meal which is high in rumen undegradable protein (UDP). This experiment investigated the response to fish meal supplementation of an energy concentrate based on either barley (starchy) or sugar beet feed (SBF, fibrous) when fed with good quality (64‘D’) grass silage to cattle in the finishing period of a traditional 18 month semi-intensive system.

Forty two 15 month and twelve 14 month old Friesian steers were blocked by weight and allocated at random to treatments (weights as fed):

• 1. 2kg barley plus minerals (2B)

• 2. 1.8 kg barley plus 0.2 kg fish meal (2BF)

• 3. 2 kg sugar beet feed plus minerals (2S)

• 4. 1.8 kg sugar beet feed plus 0.2 kg fish meal(2SF)

• 5. 4 kg sugar beet feed plus minerals (4S)

• 6. 4 kg barley plus minerals (4B)