1995 ^. Volume 18, Number 4

Mature animals typically consume enough feed to meet their energy requirements based on the size or weight of the animal. For example, an animal weighing in at 300 lb. will consume less feed than a one weighing in at 400 lbs. Thus, first parity gilts will not consume the same amount of feed as multiparous sows. However, the gilts nutrient needs are similar to (or exceed) those of sows if they are nursing the same number of pigs. Often times, one may observe an average of 2 to 3 lb. difference between first parity sow intake when compared to multiparous sows. It is not uncommon to observe gilts eating 8 to 10 lb. during an average lactation, compared to 11 to 13 lb. for sows. As a consequence, the potential for poor reproductive performance is greater in first-parity gilts due to lower nutrient intakes. Several methods exist for offsetting this problem, but the implementation of these programs is very producer dependent. The producer may choose to have the lactation diet formulated to meet the gilts need, rather than that of the mature sow. However, this is a very expensive alternative, unless a method of supplying both a gilt and sow diet can be found. Alternatively, the producer may opt to develop of a sow/gilt supplement. Several commercial supplements are available, and development of such a supplement will be discussed in a later issue.

Current research suggests that sows and gilts require no less than 44 g of lysine per day when nursing moderate to large litters. This is substantially higher than NRC (1988) recommendations, and probably represents genetic progress, improved reproductive performance, and reduced mortality over the past three decades. One rule of thumb that has been taught in the past suggested that the sow needs approximately 4-4.5 lb. of feed for herself (or the quantity normally fed during gestation) and 1 lb. of feed for each piglet she is nursing. Thus, if the sow is nursing 8 pigs, she only needs to consume about 12 to 12.5 lb. of feed during lactation. The diet in this situation would be a corn-soybean meal diet formulated to about .7% lysine. Iowa State researchers (Sauber et al., 1995) suggest that the sow only requires about 3 g lysine/d and each piglet requires about 4 to 4.5 g lysine/d. Thus, for the sow nursing 8 pigs and eating 12 lb. of feed, her requirement is about 37 g lysine/d (3 g for sow, 4.25 g/pig). This can easily be met by using a diet containing .7% lysine (12 lb./d × .007 lb. lysine/lb. feed × 453.6 g/lb. = 38 g lysine/d consumed). However, if the sow is nursing 10 pigs, she needs to consume about 14 to 14.5 lb. of feed during lactation to meet her nutrient needs. Sows will not eat this quantity of feed, so adjustment of the diet is required for sows nursing large litters. An example of how to determine dietary lysine needs based on daily feed intake is provided in Table 1.

It is obvious that changes in diet formulation are necessary to meet the changing needs of lactating sows. However, it appears that changes in the number of piglets nursing the sow and differences in daily feed consumption account to a large extent for the differences between current and past recommendations. As researchers develop a better understanding of how nutrients are partitioned, diet formulation will become easier and more precise. It is not specifically known if different genotypes partition nutrients differently to a significant degree to justify reformulating diets. However, as we have changed genetic bases, these issues become confounded with changes in litter size and daily intake. Currently, you can use the data presented here along with known feed consumption's to determine the dietary nutrient needs for your animals.

Jeffrey A. Hansen

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