14 November 1997

Fishmeal replacements work – but more research needed

FISHMEAL can be replaced by vegetable proteins without affecting sheep production. However, ewes fed fishmeal required less assistance at lambing.

Thats the conclusion of trials at SAC Edinburgh, but sheep specialist John Vipond warns that care is needed in extrapolating trial results to farm conditions.

"It appears that it is possible to replace fishmeal in ewe rations without detriment to production. But trial results may not reflect what happens on farm where there is often more stress on ewes and less labour available."

The SAC trial looked at the effect of fishmeal and several alternative vegetable proteins fed alongside a hay-based diet on ewe condition pre- and post-lambing, blood test results, lamb birthweight, colostrum production and quality and assistance at lambing.

Prior to the trial, the 150 Scotch Mule ewes selected – weighing about 80kg and with body condition scores of around 3.6 – were offered ad lib hay and 0.1kg/head/day ewe nuts. They were then divided into groups of 25, offered hay ad lib and randomly allocated to a specific diet.

The control group was fed 19% barley, 19.9% wheat feed, 20% maize gluten, 15% citrus pulp, 8% Hi-pro soya, 3% rapeseed meal, 5% fishmeal, 2.5% fat premix, 5% molasses and 2.6% vitamins and minerals. This ration gave 180g crude protein/kg fresh weight, and an ME of 12.5 MJ/kg DM.

"We tested three vegetable-based fishmeal replacers from Rumenco and Nutec and two compounds from Dalgety currently in development which aimed to be equivalent to an inclusion rate of 5% fishmeal," explains Dr Vipond.

Ewes received concentrate at 0.1kg/head/day initially, increasing to 0.35kg/head/day after a week, and stepping up to 0.75kg/head/day, offered in two feeds, after three weeks. This level was maintained until after lambing, with ewes receiving 20.4kg concentrate a head pre-lambing.

Rations provided 80-85% of ewes ME needs over the last six weeks of pregnancy, aiming for a body condition of half a unit to lambing.

Dr Vipond points out that though loss of body condition is usual practice, it places strain on the ewes metabolisable protein balance – resulting in lower yields of bacterial protein being supplied to the small intestine. This allowed more rigorous quality testing of proteins, but little difference was found between any of the feeds.

"There were no differences in ewe body weight or body condition score changes pre-lambing. All ewes lost about half a condition score unit pre-lambing – as planned. However, blood tests showed that none of them were under nutritional stress."

The only difference to emerge from blood tests was that ewes fed fishmeal had lower than average blood ureas. "We would expect ewes fed vegetable proteins to have higher blood ureas as more protein is broken down in the rumen."

Lamb birthweight, and the amount and quality of colostrum were similar for all feeds. However, ewes fed fishmeal required less assistance at lambing.

"Only three out of 24 ewes in the control group required assistance, while the average number assisted on vegetable-derived protein rations was 11 out of 24 ewes. Thats a significant difference."

However, Dr Vipond says he has no idea why there should be such a difference, particularly as all other factors were the same.

"It could be chance, or it could be a genuine finding in that ewes fed fishmeal have fewer malpresentations. But to feel confident about the result it would have to be repeated in further trials."

And although most cross-bred ewes will probably produce sufficient milk on a ration including vegetable-derived proteins, Dr Vipond says that fishmeal may give greater benefits when fed to terminal sire breeds, which produce inherently less milk.

"Im not convinced that fishmeal is essential, but I would also say that producers should be careful about removing it from rations."n

FISHMEAL v VEG PROTEIN

&#8226 Less assistance.

&#8226 Lower blood urea.

&#8226 All other factors similar.