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Gilts: Rearing for Maximum Protein Gain or Back Fat?

by 5m Editor
26 August 2010, at 12:00am

It is important to meet the protein requirements of the gilt to prevent a delay in reaching puberty or a reduction in ovulation rate, according this BPEX publication in the series Research into Action.

Over the last 10 to 20 years, selection has led to the development of very lean genotypes that have very different body composition to those previously, including:

  • they mature later (later puberty)
  • they are heavier and leaner
  • they have a higher ovulation rate (but ovulate smaller, lower quality oocytes), and
  • they are more likely to return to heat during lactation.

Figure 1. Gilts fed low-lysine diets during rearing. P2 values were 4 to 5mm greater than those fed a high-protein diet

Figure 2. Gilts fed high-lysine diets during rearing. Gilts appeared fatter than those fed low-lysine diets but, in fact, they had lower P2 values

In these modern lean genotypes, body protein mass may be more important than backfat for lifetime performance and changes in body condition will primarily arise from gains and losses in lean mass and, to a lesser extent, body fatness. Based on recent studies (Foxcroft, 2005; Meat and Livestock Commission, 1998; Rozeboom et al, 1996; Williams et al, 2005), there may be a very poor relationship between lifetime productivity and level of body fat. This may reflect the fact that the majority of tissue mobilisation in young lactating sows is protein and not fat.

Data indicated that on many farms lifetime productivity ranged between 30 and 40 piglets per sow and only a few sows achieved the potential of 60 or more. To achieve profit from a sow, at least three litters are required and with 40 to 50 per cent of sows being culled before they reach their third parity. This is an area which should be given careful consideration.

Although measuring backfat does still have a place, weight and general body condition may be more useful measures for assessing gilts and deciding whether or not they are suitable for breeding. However, care must be taken as Figures 1 and 2 illustrate how a visual assessment of gilt body condition can be misleading in terms of fat and protein deposition.

Longevity will be improved by avoiding rapid weight gain before first service. Research indicates that the ideal weight range at first service is 135 to 150kg, with a body condition score (BCS) of 3.

If gilts weigh much less than 135kg at first service, there is a risk of the following problems occurring:

  • low bodyweight at first farrowing
  • low body reserves at first farrowing
  • high anoestrus rate after first weaning
  • high risk of early culling, and
  • low production over first three parities.

Conversely, if gilts weigh more than 150kg at first service, the following problems may occur:

  • high body weight at first farrowing
  • high gilt cost to first farrowing
  • high nutrient requirements, and
  • high risk of early culling.

The feeding programme should limit weight loss during lactation and ensure young sows are able to maintain condition during subsequent pregnancies to farrow with a BCS of 3.

Diet specification (lysine and DE) by stage of production
Stage Lysine (%) MJ DE/kg
Up to first service (100–135kg)* 0.9–1.0 13.8
Gestation 0.7–0.8 13.5
Lactation 1.0 14.5
* restrict intake to 80–90% appetite

A major consequence of not meeting the protein (or amino acid) requirements of the gilt can be a delay in reaching puberty and a reduction in ovulation rate, both of which are costly in terms of productivity.

Weight and body condition are only two of the factors that influence gilt performance and longevity.

Considered alone, they will not guarantee good lifetime productivity but they are two of the major reasons for poor performance and premature culling, along with lameness.

The performance of gilts and young sows should be evaluated and discussed with the unit’s nutritionist, vet and breeding company and appropriate feeding strategies decided. This should take place on a regular basis as gilt requirements can change over just a few years.

August 2010