Can You Extend the Length of Gestation?

by 5m Editor
21 June 2011, at 12:00am

Altrenogest (Matrix) can be used to delay the onset of farrowing if circumstances dictate such a management intervention although it delayed nursing in piglets in litters from gilts, writes Ronald O. Bates, State Swine Specialist at Michigan State University in the latest issue of Pork Quarterly from MSU.


There are several products available within the swine industry to assist in reproductive management of the sow herd. Products like P.G.600® can synchronise the onset of oestrus among non-cycling females. Matrix® will synchronise oestrus in cycling gilts and products like Lutalyse® and Prostamate® will induce farrowing for females about to farrow. However, the question does come up, “Can you ‘hold’ a sow from farrowing?” In other words, can some product be used to delay the onset of farrowing? This could be useful when there are more sows to farrow than farrowing stalls to put them in. An extra day or two may allow a farm either to early-wean or to cross–foster enough litters to open up stalls to put sows into before they farrow.

Matrix is synthetic progestagen that acts like progesterone in pigs. Progesterone is the primary signal that maintains pregnancy. It can be used to synchronise oestrus or heat in cycling gilts by ‘fooling’ the gilt to ‘think’ it is pregnant. When Matrix is no longer fed, the gilt’s biological system takes over and the gilt comes into heat. However, the question comes up from time to time if Matrix can be used to delay the onset of farrowing. The product elevates plasma levels of progesterone like compounds so it does make sense that it could be used to ‘fool’ the gilt and not allow the gilt’s biological system to begin the farrowing process as farrowing day approaches.

There have been several studies to show that this is possible. A recent study (Foisnet et al., 2010) investigated feeding altrenogest (Matrix) from day 109 to day 112 or 113 of gestation and determined how it impacted the length of gestation, along with several other litter performance characteristics. In this study, 20mg/day of altrenogest was fed to pregnant gilts starting on day 109 of gestation. One group of gilts was fed altrenogest for four days (including day 112 of gestation), while another group was fed altrenogest for five days until day 113 of gestation. These two treatment groups were compared to an untreated control group of gilts. Sows were not induced to farrow. Litters were kept with their birth mother for the first 24 hours and then cross-fostered to standardise litter size at 12 piglets. Farrowings were attended and piglets were weighed at birth, at 24 hours and at weaning. Piglets that had not nursed within 40 minutes of birth were assisted. Colostrum yield during the first 24 hours after farrowing was estimated. Litters were weaned at approximately 25 days of lactation.

The altrenogest treatment was successful in delaying farrowing (Table 1). Gestation length for control sows was 114.7 days, while those fed altrenogest from day 109 to day 112 and day 113 had gestation lengths of 115.8 and 116.3 days, respectively. It appears that sows farrowed two to three days after altrenogest was no longer fed. Duration of farrowing appeared to be shorter for sows fed altrenogest compared to controls; however, this was not significant.

Table 1. Influence of feeding altrenogest in late gestation a
Item Control Day 109-112 b Day 109-113 b
Gestation length, days 114.7 c 115.8 d 116.3 d
Duration of farrowing, minutes 238 (1 hr, 59 min.) 157 (2 hr, 37 min.) 189 (3 hr, 9 min.)
First time to nurse, minutes 25 e 18 e 34 f
Colostrum yield first 24 hours after farrowing, lb 9.3 c 10.5 c 8.3 d
Average piglet weight on Day 1, lb 3.2 3.4 3.0
Average piglet weight at weaning, lb 15.8 16.1 15.6
aAdapted from Foisnet et al., 2010
b Altrenogest was fed from Day 109 of gestation to either day 112 or day 113
c,d Means within a row with different letters differ (P<0.10)
e,f Means within a row with different letters differ (P<0.05)

An interesting result was that the time for pigs to nurse after they were born was influenced by treatment (Table 1). Piglets from gilts that were fed altrenogest to day 113 of gestation took approximately 12 minutes longer, on average, to begin nursing after they were born than piglets from control gilts or those fed altrenogest to day 112. Colostrum yield was also influenced by treatment. Gilts fed altrenogest from day 109 through day 113 of gestation had slightly less colostrum yield than control gilts or those fed altrenogest through day 112. Even though piglets from sows fed altrenogest to day 113 of gestation took longer to nurse, treatment did not influence piglet weight 24 hours after birth and averaged 3.2lb. Average piglet weaning weight (15.8lb) also was not influenced by treatment.


Altrenogest (Matrix) can be used to delay the onset of farrowing if circumstances dictate such a management intervention, such as a lack of open farrowing stalls for sows ready to farrow. Gilts that were fed altrenogest from days 109 to 113 farrowed piglets that took longer to begin nursing. However, piglet weight at 24 hours after farrowing and at weaning was similar across treatments.

Final Thoughts

The dosage used in this study (20mg per day) is 5mg higher than the recommended dosage to be used among cycling gilts to synchronise oestrus. The label dosage for synchronising oestrus in gilts may not yield the same results that were observed in this study. It should also be mentioned that farrowing was supervised intensively and piglets that did not nurse within 40 minutes were assisted to consume colostrum. If farrowings had not been assisted, the mean time from birth to initial nursing, for pigs born to gilts fed altrenogest to day 113 may have been greater. This also could have influenced pre-weaning mortality, which was similar across treatments. Producers considering using this product to delay the onset of farrowing, must consult with their veterinarian regarding this off-label use.

Literature cited

Foisnet, A., C. Farmer, C. David, and H. Quesnel. 2010. Altrenogest treatment during late pregnancy did not reduce colostrum yield in primiparous sows. J. Anim. Sci. 88:1684-1693.

June 2011