Over the first 30 to 40 years of intensive, technologically enhanced pork production, slow and steady progress has been made toward understanding the factors that influence sow longevity.

At times, this improvement seems to have come with three steps forward and two steps back.

The steps backward are best illustrated by gilt replacement rates of 60% and double-digit sow mortality rates.

The steps forward are reflected in new information about improved breeding herd longevity recently reported by researchers here at Michigan State University.

The effects of a growth-altering, pre-pubertal feeding regimen on gilt growth, first-parity lactation performance and reproductive longevity were evaluated in a multi-year study. From February to August 1998, 16 groups of early weaned (10 ± 2 days of age), Yorkshire x Landrace gilts were moved into the newly constructed swine facility in East Lansing.

In the nursery phase, all gilts were reared using typical commercial diets and production practices.

At 9 weeks of age and about 50 lb. live weight, 252 gilts were allotted to one of two, 16-week, nutrition regimens that we termed “moderate” or “control” (Tables 1 and 2).

Moderate regimen gilts were intermittently provided with ad libitum access to either high-fiber or conventional corn-soybean meal diets in order to achieve alternating periods of moderate and maximum growth. High-fiber diets, fed during periods 1 and 3 to slow growth, contained 35% ground sunflower hulls. During periods 2 and 4, corn-soybean meal-based diets (the same diets fed to control gilts during those periods) were fed for compensatory growth. Control gilts were given ad libitum access to corn-soybean meal-based diets in all periods to maximize growth.

The nutritional regimens resulted in two different growth patterns for gilts from 9 to 25 weeks of age. Figure 1 shows live weight differences and Figure 2 illustrates accompanying average daily gains.

Moderate gilts grew more slowly during periods when fiber was fed, and grew faster when given conventional corn-soybean meal feed. Compensatory gains were greatest in period 4, when gilts were older and able to consume greater amounts of feed (Figure 3).

Gilt Management

After the experimental grow-finish phase, all females were managed similarly so that only the effect of grow-finish growth pattern on longevity would be evaluated. Knowledge of these replacement gilt management practices is critical in interpreting the results of longevity studies.

In this study, gilts were moved from grow-finish rooms to the breeding room at about 27 weeks of age (roughly 187 days of age). For the two weeks between the end of the experimental feeding phase and this move, all gilts were given ad libitum access to the last grow-finish diet (Diet E).

Immediately after moving to the breeding room, gilts were monitored daily for signs of estrus using the presence of a boar. From the time they were moved until puberty, gilts were given ad libitum access to a standard breeding herd corn-soybean meal-based diet containing 10% wheat bran (0.65% lysine, 0.9% calcium, 0.8% phosphorus).

Age at puberty was similar for moderate and control gilts, averaging about 204 days of age. At first estrus, gilts were weighed, moved into individual crates, and fed 5 lb. of the breeding diet per day. Gilts not showing first estrus by 285 days of age were removed from the experiment.

Fourteen days prior to second estrus, feed offered was increased to 7 lb./day to flush gilts. Gilts were artificially inseminated at second estrus with pooled Duroc semen. Gilts were serviced each morning of standing heat. Those returning to estrus a second or third time were rebred. Gilts returning to estrus a fourth time were culled.

In gestation, gilts were given 3 lb./day during the first week post-service, and 4, 5, 6 and 4 lb. of feed daily, from weeks 2 to 7, 8 to 13, 14 to 15 and 16 to farrowing, respectively.

In subsequent parities, sows received 4.4 lb. of gestation feed per day. Lactating sows were provided ad libitum access to feed and weaned when piglets were 19 to 20 days old.

Al Snedegar, farm manager, made all culling decisions. He was “blinded” to previous nutrition regimen assignments by being absent at the end of the grow-finish phase when all ear tags were changed. Ear tags that were used to identify rearing treatments were removed and replaced with non-distinguishing sow herd tags.

Reasons for culling were separated into “voluntary” and “involuntary.”

Voluntary culling was a consequence of a managerial decision.

Involuntary culling was the removal of females because they were unlikely to produce as desired or in an acceptable time (see Table 3).

Growth's Impact on Longevity

Grow-finish treatment influenced the incidence of culling. At the start of the grow-finish phase, there were 128 moderate gilts and 124 control gilts. Fewer moderate gilts were culled prior to weaning their first litter than control gilts. Locomotive failure was the most prevalent reason for culling. Of the females culled prior to completing their first parity because of locomotive failure, 13 were controls and only two were moderates.

The effect of pre-pubertal feeding programs on sow longevity after parity 1 was also recorded. All sows were culled by the end of parity 8.

Average parity completed for gilts started at 9 weeks of age and involuntarily culled were 1.5 and 2.2 for control and moderate treatments, respectively. Put another way, 33.3% of control females and 60.4% of moderate females allotted at 9 weeks of age completed parity 3.

These numbers initially suggested that more control females may have been culled throughout the study, but this was not true. Of the sows completing parity 1 (64 controls and 92 moderates), equal proportions went on to complete parities 3, 4, and 5. Grow-finish nutrition did not alter the incidence of involuntary culling after parity 1 for any reason.

In conclusion, the MSU study suggests that the intermittent feeding of high-fiber diets to gilts in the grow-finish phase will alter growth pattern and decrease the incidence of culling of females early in life (prior to completing parity 1). Fewer gilts may be culled for reasons primarily associated with locomotive failure. Sow longevity after parity 1 is not expected to change.

Researchers included Pasha Lyvers-Peffer, Jiajiang Peng, Alan Snedegar and Dale Rozeboom.

Table 1. Diets Fed During the Four Pre-pubertal Periods to Comprise the Two Nutritional Regimens Used to Alter Growth Pattern in Developing Gilts

1 2 3 4
Duration, weeks 3 3 5 5
Control regimen A A C E
Moderate regimen B A D E

Table 2. Composition of Experimental Diets (As-fed Basis)

Ingredient, % A B C D E
Corn 62.26 36.20 71.95 39.57 75.87
Sunflower hulls - 35.00 - 35.00 -
Soybean meal, 44% crude protein 30.26 22.42 20.56 19.26 17.96
Calcium phosphate dicalcium 2.07 2.73 1.98 2.52 1.74
Ground limestone 0.84 0.55 0.81 0.55 0.83
Choice white grease 3.00 1.50 3.00 1.50 2.00
Vitamin premix 0.60 0.60 0.60 0.60 0.60
Trace mineral premix 0.50 0.50 0.50 0.50 0.50
Salt 0.50 0.50 0.50 0.50 0.50
L-lysine HCL, 78.8% - - 0.10 - -
Calculated analysis
ME, Mcal/lb. 7.5 5.0 7.5 5.0 7.5
Lysine, % 1.03 0.74 0.86 0.66 0.71
Crude protein, % 18.6 15.7 16.2 14.5 16.2
Calcium, % 0.88 0.88 0.83 0.83 0.77
Phosphorus, % 0.75 0.75 0.70 0.70 0.65

Table 3. Effect of Pre-Pubertal Feeding Regimen on Longevity Through Parity One

Gilt pool Breeding to parity-one weaning
Reason for culling Control Moderate Control Moderate
Unsound underline 2 1 - -
Locomotive failure 7 1 4 1
No puberty by d 285 2 1 - -
Anestrus post-puberty 1 - - -
Failure to conceive - - 16 12
Abortion - - 5 1
Failure to farrow - - 6 5
Savage sow syndrome - - - 1
Unknown* - - 1 -
Locomotion - - 2 -
Voluntary 2 2 9 11
Total culls 14 5 43 31
*Three control gilts died from unknown causes during the rearing period.