27 October 1995

Selection snags in lean growth work

SELECTION for genotypes conferring rapid lean growth over the past 10 years has produced pigs with lower appetites, limiting their ability to cope with increasing production demands.

So said Dr Sandra Edwards of the Scottish Agricultural College at a meeting organised by Roche Products at farmers weeklys Easton Lodge Farm, Stamford, Lincs.

"As lean tissue growth rate has increased, mature body size has risen, increasing maintenance requirements of dry sows," said Dr Edwards. "At the same time milk yields have risen and litter sizes have increased with the introduction of hyper-prolific sows.

"This means feed intakes achieved by sows in practice nearly always fall short when medium density diets are used, contributing to higher sow culling rates because of reproductive failure."

To promote body fat reserves without increasing body size a National Pig Development Company and SAC study limited lean tissue growth by restricting protein intake in gilts before mating and during pregnancies.

Gilts were fed a low protein diet of 13MJ/DE/kg and 11.3% crude protein, enabling them to deposit more fat. During lactation they were fed a high density, 14.8MJ/DE/kg, 18% CP diet with high oil content to conserve body reserves at a time of high lactation demand and limited feed intakes.

This was compared to a standard single feed of 13 MJ/DE/kg with 16% CP.

"At first service gilts had P2 values of 15mm to 16mm and those fed two diets showed increases in fat reserves at farrowing without increasing liveweight or feed requirement, and reduced fat loss in lactation," said Dr Edwards.

"Single-diet animals lost more weight and fat in lactation and had to be fed at higher levels to regain condition in following pregnancies.

"Litter size and growth rate did not differ significantly but rebreeding was better with two diets," she said.