Big improvements in weaned pig diets, disease eradication strategies and sow performance have shortened average lactation lengths. Many U.S. producers wean sows at 18-21 days, in striking contrast to the 42-day and 28-day lactation lengths in the '70s and '80s, respectively.

Perhaps no other management decision impacts sow performance, facility use and pig flow as much as lactation length.

A short lactation length (12-14 days) holds pig health and performance benefits. But, sow physiological limitations restrict lactation lengths to about 17 days for consistent breeding and reproduction performance.

It's vital to understand the impact of altering lactation lengths. Some sows can reproduce well on 12-day weaning schedules; others experience numerous reproductive problems.

Additionally, greatly altering lactation length can require a large financial investment in remodeling.

This article addresses factors limiting the success of early weaning and describes intervention strategies.

Physiological Limitations Producers face several difficulties in implementing early weaning strategies. Unlike other species, the sow remains in a state of anestrus during lactation. In this state, two events occur that affect her ability to produce a large litter.

First, ovarian and pituitary hormonal activities are suppressed throughout lactation by the suckling influence of the baby pigs. Second, this activity stimulates the release of a hormone called prolactin. The combination of these two events is believed to be mainly responsible for this anestrus period. Prolactin levels gradually decline during lactation as suckling decreases or stops.

In the ultimate early weaning system, the litter would be removed immediately after farrowing. However, it appears the suckling stimulus is actually needed for about three days for normal resumption of reproductive hormone (luteinizing hormone, LH) activity. Therefore, the mythological 3.0 litters/sow/year eludes us - for now at least.

After weaning or suckling is reduced, an increase in blood levels of LH and estradiol work to stimulate estrus. It appears this hormonal suppression provides the female time for uterus repair for future pregnancies. This regenerative process is called uterine involution.

The sow's uterus rapidly begins to lose length and weight during the first two to three weeks of lactation and continues until after weaning. If breeding occurs too soon after farrowing, it appears that uterine conditions are not favorable for successful fertilization or implantation.

The rate of uterine involution and subsequent embryonic deaths have often been linked to lactation lengths under 19 days.

Sow Challenges Decreasing lactation length creates challenges to female reproductive performance and may also mandate major building changes. Most notable is the conversion of farrowing space into nursery space. In doing so, producers must weigh the benefits of improved piglet health and a modest increase in pigs and litters/sow/year, with the potential for variable wean-to-estrus intervals, farrowing rate and litter size reductions when weaning below 17 days and more anestrus.

Thus, as producers expand or build new units to accommodate early weaning, large deviations in sow reproductive performance can result in poor facility utilization as biological targets become harder to meet.

Large variations in sow performance often occur between herds with similar management strategies and similar lactation periods. Therefore, the key point may be whether reducing lactation lengths should be based on current performance levels and conventional lactation lengths. Existing reproductive problems are likely to continue, if not worsen, by reducing weaning age.

Factors Affecting Reproduction Numerous factors contribute to lower sow reproductive performance. Anestrus, lower conception and farrowing rates and smaller litter sizes have been directly linked to reducing lactation length from the optimal 28-35 days.

- Season and environment - Much like humans, pigs feel heat based on temperature and humidity. Sows and boars both suffer from acute and persistent exposure to elevated temperatures and humidity.

As a result, infertility can be short-lived or a permanent disability.

In most cases, heat stress impacts reproduction when temperatures exceed 80ø F. Experiments have shown elevated temperatures increase anestrus in sows and gilts, and decrease conception rates and embryo survival. It's likely heat-stressed conditions exaggerate reproductive problems in early weaned sows. Effective cooling strategies, ventilation maintenance, lactation feeding strategies and genetic selection for more heat-tolerant animals can help reduce the seasonal effect.

- Breeding strategies - Our research suggests that lactation lengths averaging 17 days have no apparent effect on estrus and time of ovulation characteristics. Mistimed breedings are an unlikely contributor to poor reproductive performance on farms that practice early weaning.

It's important to note, as reported by others, we do see a consistent increase in return to estrus intervals of about a day when lactation lengths are reduced from 21 days to 14 days.

- Parity and nutrition - The greatest metabolic demand on the sow is during lactation. Many post-weaning reproductive problems are due to low feed intake and depletion of body fat reserves.

Lactation lengths have been shortened to conserve sow body stores, thereby reducing the interval from weaning to estrus and the likelihood of anestrus, specifically in parity-1 females. Parity-1 females have the greatest metabolic demands during lactation when they are growing and lactating.

Canadian researchers report sows weaned at 14 days have much higher body weights and backfat scores than sows weaned at 24 days of lactation.

In theory, then, 14-day weaning should improve reproductive performance and perhaps boost sow longevity through body condition maintenance. Unfortunately, this theory has not panned out. Most field reports suggest that parity-1 females are more susceptible to the negative effects of short lactation lengths. Dial and Bevier (1988) estimated that for every 10-day reduction (from 35 days) in lactation length, the wean-to-conception interval would increase by one day. Reductions in conception rate and litter size also occur.

Summarized database records from Mabry and Culberston (1998) indicate sows in their third or higher parity can be weaned, recycle and conceive efficiently at lactation lengths as short as nine days. First- and second-parity sows appear to need 14- and 12-day lactation lengths, respectively, to cycle and conceive efficiently.

From these records, it appears that a whole-herd average lactation length of 14 days is possible. But, this number is probably not suitable in all herds since some studies suggest a minimal lactation length for parity-1 sows needs to be closer to 18 days.

- Lactation feed intake - Without question, maximizing lactation feed intake is crucial to top reproductive performance. Some authors suggest poor reproductive performance can be negated by sows consuming 12.3-13.2 lb. feed/day.

In many ways, early weaned sows act like conventionally weaned, feed-restricted sows - higher levels of anestrus, increased wean-to-estrus intervals and lower conception rates.

To ensure sow lactation diets meet National Research Council guidelines, refer to Table 3.

The fail-safe approach is to provide sows with as much feed as possible during lactation, regardless of lactation length. Other plans are:

1. Increase feeding frequency: Producers who switch from feeding twice daily to three times daily report a 10-15% increase in sow feed intake. Some North Carolina farms feed four or more times daily in the summer. This strategy could effectively increase early weaned sow feed intake.

Remember, when you increase the frequency of feeding, you must decrease the amount that you feed each time. For example, if you feed 6 lb. twice a day (12 lb. total), when you increase to three times/day, you may want to feed around 6 lb. at the first feeding and 4 lb. at each subsequent feeding (14 lb. total).

2. Keep feed fresh: Sows tend to be picky eaters compared to most animals. In warm conditions, feed is more likely to spoil, especially if it contains high levels of fat. Feeding more often and feeding slightly smaller amounts are excellent ways to keep feed fresh.

3. Try liquid diets: Liquid feeding, commonly used to push feed intake in finishing, can be used during lactation.

However, because of the limited time sows spend in lactation, it may be more beneficial to acclimate females to this diet change during late gestation. Success with this strategy varies greatly, but it can reportedly boost sow feed intake up to 15%. One drawback is wet feed doesn't stay fresh long, and molds will accumulate without regular cleaning.

4. Add fat: As a result of poor feed intake, many sows aren't able to meet the metabolic demands of lactation and may fall into a negative energy balance. This situation probably accounts for most of the reproductive disorders during periods of elevated temperatures. To ensure sows consume enough energy, even though they are eating a smaller quantity of feed, add fat to the lactation diet. Supplemental fat (7-10% animal or vegetable fat) will increase the dietary metabolic energy content of the feed.

Consider two important factors in adopting this practice. First, a diet containing high amounts of fat will become rancid more rapidly than a traditional diet with only 1% to 2% fat. Sows will not eat rancid feed. Therefore, feeding smaller quantities more often and smelling feed leftover in the sow feeder at each feeding to check for spoilage should be a standard practice.

Second, because sows are consuming less feed, dietary levels of essential vitamins and minerals also need to be boosted to compensate for less feed consumed on a daily basis.

5. Give water constantly: Hot weather will increase water requirements. Increased water consumption coupled with increased urinary water loss is one mechanism by which pigs lose body heat. A temperature increase from 54-60ø F to 86-95ø F will cause pigs to drink more than 50% more water. Nursing sows need to consume 8-10.5 gal. of water every day. Gestating sows need 3-5 gal. A water-to-feed ratio of 5:1 is a good rule of thumb to follow.

Fresh, constant water is also critical during breeding and gestation. The watering system should deliver a minimum of 0.25 gal./minute and ideally 0.5 gal./minute. Sows will quickly become frustrated if the flow rate is low, and this will reduce their appetite for dry feed.

Water temperature and quality are also important. During periods of high temperatures, pigs will consume almost double the quantity of cool water (50§ F) as warm water (80§ F).

Sow Farm Personnel Farms with the same genetics, nutrition, buildings, health status and standard operating procedures can have very different reproductive responses to short lactations. This is probably true for any operation regardless of lactation length. Good sow farm personnel make significant contributions toward a successful early weaning program.

Intervention Programs The three basic ways to improve reproductive performance are: improve whole-herd reproductive parameters (i.e. piglets born alive), identify problem groups of females that are dragging down these parameters and intervene where possible and treat each sow for reproductive failures like anestrus.

Whether intervention strategies are conducted on the whole herd, sub-populations, or individual sows, carefully weigh the benefits anticipated against the practicality of the treatment.

For an early weaning system, a simple adjustment in weaning age or reduction in lactation length variations may be all that's needed to fix poor reproductive performance.

In other operations in which subtle management changes haven't worked, consider a few options.

Remember, much like the impact of reducing lactation lengths on reproductive performance will vary significantly between herds, the success of intervention programs also will vary.

Producers should first identify the major factors in a herd that may compound the physiological limitations that short lactation lengths have on the sow's ability to reproduce.

If problems persist after cost-effective attempts, decide if your facilities can handle a small increase in average lactation length without suffering a drop in health and growth performance in finishing.