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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Relationship of Sow Nutrition and Post-weaning Return to Estrus

Livestock Update, April 1999

Allen Harper, Extension Animal Scientist, Swine, Tidewater AREC

On commercial swine breeding farms, it is expected that a large percentage of sows exhibit a fertile estrus within 3 to 8 days after weaning. A varying percentage of sows, however, fail to exhibit estrus within this time span and may experience extended periods before returning to normal reproductive function. Delayed return to estrus has a major negative impact on breeding herd efficiency by disruption of breeding schedules, increasing "non-productive sow days," reducing pigs produced per sow per year, and perhaps causing premature culling of sows with good genetic potential for milk production and heavy litter weights. There is a substantial information base indicating that sow feeding and nutrition during lactation has a direct relationship on return to estrus after weaning. This article offers a brief review of the sow nutrition and return to estrus relationship with suggestions on management steps to optimize return to estrus for efficient breeding herd performance.

Low Consumption of Energy and Protein
For many years swine herdsmen and veterinarians have observed that sows which are visibly in poor condition at weaning time often exhibit rebreeding problems. But Australian researchers R. H. King and A. C. Dunkin (1986) were among the first to demonstrate the linear relationship between reduced daily feed intake during lactation and increased time required for sows to express estrus after weaning (figure 1). Further studies demonstrated that younger first litter gilts were more sensitive to the negative effects of reduced feed consumption during lactation than older gilts or multi-parity sows. It was presumed that deficient dietary energy intake by the underfed nursing sow was the principle cause of poor return to estrus after weaning. Work at the University of Nebraska (Reese and co-workers, 1982) supported this assumption. In this study protein and other nutrient intake was kept adequate for all lactating sows but energy consumption was varied among sow groups to be 8, 12 or 16 mega-calories per sow per day. Sows consuming only 8 mega-calories per day lost 57 lbs. of body weight during lactation. They also lost 8.4 mm of backfat and only 65% of these sows expressed estrus within 8 days after weaning. Those consuming 12 mega-calories per day only lost only half as much weight and backfat and over 91% were in heat within 8 days after weaning. Those consuming 16 mega-calories per day lost less weight and backfat and 96% were in heat by day 8 after weaning. Clearly getting the sow to eat enough total calories to meet the heavy demands of milk production is critical to reduce weight and fat losses during lactation and insure timely return to estrus. One nutritional strategy that has become more routine to enhance caloric intake of lactating sows is adding fat to the sow diet to increase caloric density. This has proven to be especially helpful during the summer and early fall months when sows tend to consume less feed.

Figure 1.

But what about consumption levels of protein (or essential amino acids) during lactation? The Australian animal scientists helped provide the answer to this question also. They fed groups of lactating sows diets that were high energy-high protein, high energy-low protein, low energy-high protein or low energy-low protein. Sows fed the diet high in energy and protein (approximately 13 mega-calories and 650 grams of protein per day) had an average return to estrus interval of less than 7 days while those fed the other diets required 15 days or longer to return to estrus. Therefore failure of sows to consume enough energy, protein or a lack of both during lactation will result in poor return to estrus after weaning. In effect sows nursing large litters have an excessive nutritional demand for energy and protein for milk production. If consumption is low, the sow produces milk at the expense of tissue reserves of energy (fat) and protein (muscle). If this nutritional stress becomes severe, the normal pattern of reproductive hormone release in the sow is disrupted and cyclic function after weaning is impaired.

Modern Sows and Early Wean Systems
Genetic improvements in sow productivity have resulted in an even greater need for adequate energy and protein consumption during lactation. Today's improved maternal line sows have larger mature body size and are capable of producing larger litter sizes and greater milk production. Larger body sizes increase energy and protein requirements for body maintenance while larger litter sizes and greater milk production increase nutritional needs even further.

The increase in segregated early weaning production systems has also increased the importance of sow nutrition during lactation. It has been well documented that decreasing lactation length in commercial sow herds has a negative impact on the weaning-to-estrus interval and this negative effect is more pronounced in first litter females than in multi-parity sows. In segregated early wean systems in which lactation lengths may be as short as 12 to 14 days, feed consumption during lactation is especially critical. Minnesota workers (Koketsu and co-workers, 1996) examined over 10,000 pigCHAMP records and determined that weaning age had no effect on the wean-to-estrus interval when lactation feed consumption exceeded 12.3 lbs. per day. However, when sows consumed less than 9.2 lbs. of feed per day during lactation, weaning at a piglet age of 11 to 13 days resulted in a lower subsequent farrowing rate than when weaning at 14 to 22 days of age. Based on this large data set, weaning at very early pig ages (11 to 13 days) may result in poorer rebreeding performance of sows but this reduction in performance can be largely prevented by achieving sow feed consumption rates of more than 12 lbs. per day during lactation.

Feeding Management Considerations
In order to optimize rebreeding performance in sows after weaning it is critical that a very high plane of nutrition be achieved for the sow during lactation. The following are some key considerations for managers and herdsmen striving to achieve this level of nutrition for lactating sows.

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