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).
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.