Changes in body condition of sows and gilts can have lasting effects on productivity. Provimi’s UK and Ireland technical manager, Barry Hoare (pictured), reports on trial work that shows that excessive weight loss can affect subsequent fertility and litter size
During the past decade, the number of live-born piglets in UK herds has increased by just over two piglets per litter. These extra mouths to feed challenge the milking ability of sows and we frequently find that, in high-performance herds, feed alone will not meet the nutrient demands for extra milk production. These nutrients are then drawn from body reserves, leading to bodyweight losses during lactation that can affect subsequent reproductive performance.
It’s quite normal for sows to lose weight when lactating, as it is for mammalian females in general. This isn’t a “bad” thing, but excessive weight losses should be avoided. Losses up to 11% are acceptable, providing that there’s room to recover during early gestation. Above this level could mean that sows run the risk of reduced reproductive performance in their subsequent litter.
Table 1 shows the results of a trial carried out with a group of 40 sows showing the effect of subsequent fertility performance following varying levels of weight loss.
A high lactational weight loss followed by a low litter size can have a large effect on subsequent reproductive performance, especially in young sows. Recent studies have shown that good reproductive performance in the first and/or second parity is an ideal indicator of good reproductive performance in subsequent parities. This is shown in Figure 1, where sows with a litter size of 14 piglets or higher in their second parity give 4.5 more piglets in parities three to five, compared with sows with a litter size of 10 or fewer piglets in their second parity.
It’s therefore very important to have a gilt with enough weight and backfat at the time of first farrowing. Well-developed gilts are better able to withstand lactation weight losses and perform better throughout the lactation and during subsequent litters compared with less developed gilts.
These well-developed gilts are more likely to have better feed intakes during the lactation than less-developed gilts, so lactation weight loss is reduced.
The commonly used target for bodyweight at first insemination, which is at the second oestrus during puberty, is 140kg. The age at which the gilt should achieve this weight will vary between breeds, husbandry systems and countries, but it’s typically between 210 and 240 days. Gilts should weigh between 185kg and 195kg after farrowing, which is about 205 to 215kg including piglets.
Backfat of the sow and gilt should also be considered alongside weight. First, it’s easier to measure backfat depth and, second, we know that having enough backfat at farrowing, around 17-18mm P2, allows the gilt to use body reserves for milk yield without any negative effects on reproductive performance.
Of course, there’s also a limit on backfat depth loss, with studies reporting negative effects on reproduction when backfat loss exceeds 5mm during lactation. As a rule of thumb, backfat at weaning should be at least 12mm. But gilts especially shouldn’t be allowed to get too fat as this can give problems throughout their reproductive life. Therefore, gilt rearing should focus on optimising weight and backfat development. A specific rearing diet and the right feeding curve should be in place.
Poor reproductive performance may not always be linked with earlier weight loss – the effects can be delayed and to some extent hidden. But we know from trials that high weight loss has a significant effect on reproduction, so bodyweight and backfat are very important factors to consider when optimising reproductive performance in a multiplier herd.
Even though the extra weighing and measuring seems like a lot of work, it will pay off. There will be likely benefits in being able to use a more precise ration and in managing a more uniform herd of sows. Furthermore, weight and backfat loss will be an early warning system and can be used to prevent excessive weight loss; a more proactive management approach that should bring better reproductive performance.