Genetically lean gilts

Losses of gilts and young sows due to reproductive failure and leg problems are of particular concern.

Nutritional strategies for increasing gilt productivity and improving longevity are an area of some controversy. Many advisers suggest that genetically lean gilts should be encouraged to develop sufficient fat reserves prior to mating by feeding a low protein diet. This then provides an energy reserve that is partially used in first lactation, while leaving an adequate fat level to allow successful rebreeding.

A target of 18-20mm backfat has been suggested as a target at first mating, although in practice this may be difficult, if not impossible, to achieve with current genotypes.

Recent research at the Stotfold Pig Development Unit, operated by the Meat and Livestock Commission in Britain, has investigated two nutritional strategies: the first to lay down fat by using a low protein diet and the second to feed gilts so they express their genetic potential for lean growth. A total of 455 gilts, sourced from five breeding companies, were used for the trial, which ran up to 6th parity to evaluate the effect on longevity of gilt and young sow nutrition.

Gilts were reared from 30kg on a high or low lysine diet, which, from 50kg to first mating, contained 3227kcals DE and either 1% or 0.5% lysine. From mating to first farrowing the lysine levels were adjusted to 0.75 and 0.55%.

The results suggest that attempting to increase gilt's fat reserves at first mating by reducing the protein content of the diet delays puberty and reduces litter size.

Table 1 shows the differences between gilts on the high and low lysine treatments for the period up to mating at third estrus. Eight gilts from each treatment were slaughtered - those on the high lysine diet had a P2 backfat of 11.9mm compared to 15.6mm on the low lysine treatment. The lower part of the table shows that for the remainder of the gilts, those on the low protein diet took 12 days longer to reach puberty than those on the high protein diet. They were also 13 days older at first mating and 11kg lighter than gilts fed the 1% lysine diet.



At first farrowing, gilts fed the lower protein diet produced fewer piglets born alive and less total born (Table 2). Gilts reared on the high lysine diet and changed onto the lower lysine diet during pregnancy had smaller litters than those fed the low lysine diet throughout.



Dr Pinder Gill, MLC's Pig Technical Manager, who was responsible for the trial, thinks that the results may well force a rethink on gilt feeding recommendations. "It's quite clear that restricting the growth of gilts compromises first litter size," he says. "We should allow them to express their genetic potential for lean growth because this also leads to earlier puberty and better reproductive performance."

If gilts are leaner at first farrowing, feeding during lactation needs to ensure that body weight loss is minimized through the use of high density diets and by stimulating good feed intakes.

Dr Gill feels that one way of achieving this would be to use a special lactation diet for gilts and possibly second litter sows. The longer term implications of the two nutritional treatments will shortly be revealed when analysis of the data up to 6th parity is complete and a full assessment of their effect on the cost of piglet production is made.