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Causes of regular returns to estrus: the sow

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This article covers the main sow-related factors that can cause regular returns to estrus.

Regular returns to estrus occur 18 - 24 days and 38 - 44 days post-service. A sow has a regular return (maintaining the normal duration of an estrous cycle: 18-24 days or its multiples) when fertilization of the eggs has failed or when all fertilized embryos have been lost within the first half of the estrous cycle (<10-12 days).

Under normal conditions these should make up a very small percentage of the matings, < 5%.

Sow-related causes

Management


1. Lactation length: Lactations shorter than 21 days predispose first parity sows to regular returns, and in multiparous sows the same is true for a lactation length less than 16 days.

Table 1. Sow-related factors that influence farrowing rate. Koketsu, Y. 1997

Lactation length
(d)
n Farrowing rate ± SE
(sow level)
Farrowing rate ± SE
(farm level)
8-10 146 79.7 ± 3.3cd 79.8 ± 5.1c
11-13 1005 80 ±1.2c 81.7 ± 3.1cd
14-16 1195 84.4 ± 0.6cd 83.6 ± 2.3cd
17-19 2749 83.9 ± 0.7cd 84.7 ± 2.3cd
20-22 2003 89.1 ± 0.7de 88.1± 2.7cd
23-28 682 91 ± 1.1e 90.2 ± 2.5dd

2. Recurring returns: Each time a sow returns and is serviced, she is more likely to return than when was serviced previously (the farrowing rate is estimated to be reduced by 10%). It is important to cull sows with more than two returns to estrus.

Table 2. Data from 106 comercial farms. Carlos Piñeiro. 2007

Total 1st service 1st return 2nd (or more)
return
Number of matings 131,650 16,295 4,678
Total number of matings in the study 116,172 14,387 4,220
Returns 14,525 3,374 1,108
% Returns 12.5 23.5 26.3
Number of farrowings 91,153 8,713 1,780
Fertility (%) 84.4 68.1 52.2
Farrowing rate (%) 78.5 60.6 42.2
Adjusted farrowing rate (%) 82.4 66.4 52.7
Total born 12.1 12.0 11.6

3. Wean to service interval: Sows serviced late after weaning (7 - 12 days post-weaning) are usually less fertile.

Table 3. Fertility according to the wean to service interval. Koketsu, Y. 1997.

Wean to service interval
(d)
n Farrowing rate ± SE
(sow level)
Farrowing rate ± SE
(farm level)
1-6 6299 86.6 ± 0.4c 87.6 ± 1.9c
7-12 1333 81.8 ± 1.1d 76.1 ± 4.4d
≥ 13 900 85.4 ± 1.2c 85.4 ± 2.4c

4. Post-insemination management: Stress, in all its forms, can be one of the causes of sows having a regular return to estrus. Two times are especially critical:

  • The first 30 minutes post-insemination. Stress during this time will block the oxytocin, responsible for sperm transport, which can affect the correct fertilization of the ova.
  • The first 10-12 days post-service (may be heat stress). At this time stress can easily affect the correct implantation of the embryos leading to the loss of gestation.

Table 4. Influence of post-AI management. Flowers, B. 1996

Frequency Farrowing rate (%) Born alive
Mixing sows 8//19 -7 -1.8
Moving sows 7/19 -10 -1.2

Overfeeding during the first 72 hours post-service can cause returns by reducing the levels of progesterone needed to maintain gestation.

Table 5. Effect of feeding level on embryonic survival. Aherne & Kirkwood. 1985

Feed rate Embryonic survival Progesterone
d1-3 d3-15 d28 ng/ml
1.9 kg 1.9 kg 12.4 86 % 10.5
2.5 kg 1.9 kg 11.5 77 % 3.7
2.6 kg 2.6 kg 10.2 67 % 4.5

Body condition

1. Sows that have lost more than 2 body condition points during lactation are more likely to return to estrus.

Table 6. Relationship between average intake during lactation and farrowing rate. Koketsu, Y. 1997.

Average feed intake, lactation
(kg.)
n Farrowing rate ± SE
(sow level)
Farrowing rate ± SE
(farm level)
≤ 4.2 2068 83.2 ± 0.8c 83.6 ± 2.5
4.2-5.7 4642 85.8 ± 0.5d 85.3 ± 2.4
≥ 5.7 2252 84.8 ± 0.8d 88.5 ± 2.3

2. Lameness, lesions: sows that are serviced being at a sub-optimal condition are more likely to return (Photo 1).

Photo 1. Lesion on the foot of a sow.

Photo 1. Lesion on the foot of a sow.

3. Toxicity or deficiencies: Lack of vitamins or amino acids, or presence of mycotoxins.

See the semen/boar-related causes for regular returns

Use the button above or the flowchart to continue troubleshooting the returns, or to access other parts of the tool.

Types of gestation losses that can lower the farrowing rate, detailing the different types of returns to estrus based on they occur.
Types of gestation losses that can lower the farrowing rate, detailing the different types of returns to estrus based on they occur.

Article Comments

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11-Jan-2021 j.dupuisNice support figures Enric, very useful, thank you, Jeanne😃
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