Summary

Rearing

• Feed to maximise protein gain
• Restrict feeding can reduce lameness
• Use a gilt rearing diet from 60 or 100 kg live weight.

First pregnancy

• Optimise protein supply
• Do not over feed energy
• Feed a gilt rearing diet

First lactation

• Encourage high feed intake
• Feed a gilt lactation diet

Introduction

Historically, it was believed that the level of fat reserves achieved during rearing the gilt and during pregnancy was very important in maintaining the fertility of the gilt. However it is becoming more apparent that the relationship between life time productivity of the sow and level of body fat is very poor as demonstrated in Figure 1 by Gill (2007).

Figure 1. Back fat level was not related to sow productivity

Also some of the original work which had been used to support the concept that fat level was linked to life time productivity was confounded by weight of the sows (Figure 2) (Challinor, 1996). In this work, the highest number of piglets born over 5 parities was obtained from sows with a P2 at mating of 20mm but this result could also have been interpreted as an effect of animal weight or indeed, protein mass. Today the evidence is very strong that the main nutritional effect affecting reproductive performance is the level of body protein.

Figure 2

Rearing the Gilt

The mature weight of the breeding female has steadily increased over the years. Sow weight at weaning in 1967 has been documented at less than 180kg whereas in 1993 an equivalent weight was 250kg and animals have been slaughter at weights up to 500kg. Animals with larger mature weights are generally leaner and contain less fat at a given age than less improved genotypes. This results in animals depositing much greater quantities of lean tissue during their first and possibly second parity which must be allowed for in nutrient supply.

The major consequence of not meeting the protein requirement of the gilt is a delay in age at puberty and a reduction in ovulation rate. However there are few documented long-term effects of gilt rearing regimes on overall sow productivity. In fact, where culling for leg problems is a significant issue, a reduction in the growth rate of the gilt, from approximately 60kg live weight, by restricted feeding can reduce the problem. This will reduce ovulation rate unless an increased feed level is supplied for a period of 11 to 14 days prior to service. The effect of providing an increased feed level over this period was thought to be primarily due to an increase in insulin levels caused by an increased starch intake (Anderson and Melampy, 1972) but more recently Crisol et al. in 1997 demonstrated that flushing with protein also increased the rate of ovulation (Table 1).

The gilt therefore appears to have an innate need to reach a certain protein mass to achieve optimum reproductive performance. It is therefore recommended to feed a diet to growing gilts that allows protein deposition to be maximised unless lameness is a significant issue where a degree of feed restriction may be advantageous.

Nutrition During First Pregnancy

Following service evidence is available which demonstrates that embryo survival may be improved by almost 30% when a low feed intake is adopted for a period of 14 days (Jindal et al., 1996). This is believed to be due to high feeding levels causing an increase in the metabolic clearance rate of progesterone which is necessary to maintain pregnancy. The lower levels of progesterone which remain are believed to be insufficient to support the total number of embryos and hence embryo mortality increases. What has also been observed, but not fully explained, is that a higher lysine diet supplied in gestation has shown a significant increase in the number of piglets born per litter (MLC, 1999). This work suggests that a lysine level of approximately 0.7% may be needed during the first gestation. Other research has also supported the view that a higher lysine level may be required in the first gestation (Kusina et al., 1994). The work of Kusina (Figure 3) demonstrated that a lysine intake of 16g per day during gestation allowed a higher growth rate of piglets during the subsequent lactation. This was thought to be due to the ability of the sow to use the increased body protein mass to support an increased lactation since dietary protein has been shown to have little effect on mammary development.

Figure 3. Lysine in gilt pregnancy increases piglet gain in lactation

The level of fatness of sows during gestation should be controlled for several reasons:

• Mammary development can be impaired by feeding high energy levels during mid- to late pregnancy (3.5kg per day)
• High fat levels can reduce intake in lactation particularly in hot conditions
• Fat sows have a lower milk yield unless given a high protein diet in lactation.

The main benefit of body fat levels to the sow is one of welfare in that it affords protection and reduces the incidence of shoulder sores but an energy intake of 30 MJ digestible energy (DE) per day during mid-pregnancy of the gilt should be sufficient. Outdoors, fat also provides insulation, which is of importance in exposed conditions especially during winter.

Nutrition During First Lactation

In addition to lameness, another major cause of culling young breeding animals is reproductive failure. The reason for failure can often be linked to excessive loss of condition during lactation. It has also been shown that an increase in first litter size is related to a drop in the size of the second litter this may be due to the loss of body weight during the first lactation. A reduction in feed intake whether from day 1–21 or day 21–28 of lactation significantly reduces subsequent ovulation rate and increases weaning to service interval. Also restricting feed from day 21–28 of lactation significantly reduced embryo survival by over 25% but restricting before this period had no effect. All feed restriction treatments resulted in a significant increase in sow weight loss (Table 2).

It has also been demonstrated that feeding higher protein levels in lactation can reduce the weaning to conception interval (Sinclair et al., 1996), which is associated with reduced sow weight loss. As long ago as 1986, King and Dunkin showed that a reduction in protein loss during lactation gave a linear reduction in the weaning to oestrus interval. Previous work has demonstrated that a reduction in sow weight loss during lactation increases the size of the next litter. In general, a reduction in sow weight loss of 10kg in lactation resulted in an increased litter size of 0.5 piglets. It has been shown that weight loss can be reduced by increasing the protein content of the lactation diet. Similarly, an increase in the lysine level of the lactation diet has given benefits (Figure 4) and the total number of piglets born in the next litter was increased linearly as the level of lysine fed during lactation was increased up to 61g lysine per day (Tritton et al., 1996).

Figure 4. Increasing lysine intake increases size of next litter

The genotype of the sow can also affect the response to additional protein during lactation (Figure 5). Feeding a higher protein diet to Meishan-based stock did not increase milk production in the first lactation but did in later lactations. The reason for this may be that using the dietary protein to maintain the lean growth rate of the sow may take priority over milk production during the first lactation when the demand for lean growth is still high. However during subsequent lactations, the Meishan sow may have achieved her maximum lean mass and consequently additional dietary protein may be used to support further milk production (Sinclair et al., 1996). This is not the case with white type breeds with a very high lean tissue growth rate. These extreme animals have a much larger mature weight and continue growing lean tissue well into their second parity. Therefore an increase in dietary protein does not increase milk production but is used to increase the growth of sow lean.

Figure 5. Response to dietary protein level depends upon lean gain of animal

With more conventional genotypes raising dietary lysine levels sufficiently has been shown to increase milk production however this must be associated with the correct balance of dietary energy as demonstrated by Tokach et al., in 1992. This work demonstrated that an optimum level of dietary lysine relative to digestible lysine was 0.72g lysine per MJ DE in primiparous sows (Figure 6).

Figure 6. Lysine and energy must be balance to maximise milk yield