21 June 2002

Ways to boost rape meal levels in diets

PROCESSING methods used to produce rape meal can have a large effect on its nutritional value and suitable inclusion level in dairy diets.

At the conference, ADAS researcher Angela Moss explained that the maximum rape meal inclusion level in dairy diets was currently about 15%, but there were opportunities to increase it. "Although energy content of rape meal is comparable to wheat, producers are cautious about including too much in diets, believing it may lead to poor fertility, lameness and reduced performance."

Dr Moss had compared a dairy cow control diet containing soya and rapeseed meal as protein sources with one containing rape meal as the main source. "Milk yield on the high rapeseed meal diet dropped by 5.2kg/day compared with the control. Milk urea levels were also high, due to poor protein use by cows, making milk unsuitable for cheese making."

The poorer performance on the high rape meal diet was mainly due to high levels of rumen degradable protein (RDP) in the diet, but heating rape meal at 120C for 35 minutes increased its undegradable protein content. "Feeding 32% of treated rape meal and a little untreated rape meal, so cows had sufficient RDP, had no adverse effect on milk yield and quality compared with the control soya and rape meal diet."

Even feeding heat treated rape meal at 32% for a whole lactation, rather than the initial 12 weeks, had no adverse impact on cow health, fertility or production compared with the control, according to Dr Moss.

Her research also shows untreated rape meal from some sources has equal nutritional value to rape meal heat treated specifically for the study. "All rape meal is not the same. We have recently secured HGCA funding to look into the variation in meals from different processors and between rape species."

Rape meal is not all the same, as Angela Moss found out in recent studies.