tion but subsequently early pregnancy loss and, then late returns suggest late pregnancy loss. Additionally, 33% of the first-returned females had a second return in the same or a later parity. For example, 21% of the first- returned gilts had a second return in the same parity 0, and another 20% had a second return in a later parity from parity 1 to 6 or higher. So, to decrease non-productive days, one needs to pay attention to returned gilts and sows. In gilts, summer servicing increases three types of returns. Also, increased gilt ages at first-mating increase late return risk. In con- trast, low gilt age at first-mating increases regular returns, but not related with irregular returns. For sows, summer servicing, lower parity, farrowing more still- born piglets and having a WMI of seven days or more increase three types of returns. In lifetime, 33.5% of serviced females had one or more returns. These returned females had 41.5 more life- time non-productive days than non-return females. Producers need to closely monitor females in the high risk groups to reduce their return-to-service intervals of non-productive days.


preservice mean daily temperatures for individual pigs obtained from local weather stations close to the herds. This way, pro- ducers were able to predict how farrowing rates are likely to decrease by parity, based on the information from local weather news on TV. Lower feed intake during lactation also decreases farrowing rate. This is particularly the case with parity 1 sows where low feed intake during lactation is a detrimental factor related to farrowing rate. In addition, herds performing first insemination immediate- ly after first detection for gilts, had a 8% higher farrowing rate than those with later times for insemination. So, insemination timing is critical for farrowing rate, especially in gilts.


Reservice interval Approximately 10% of mated females have a return and they are reserviced. There are three types of reservice interval: regular (18- 24 days), irregular (25-38 days) and late returns (39 days or later). Gilts have more regular returns than sows, and sows have more irregular returns than gilts. What follows is that gilts have a prob- lem that is different from sows in terms of returns. The regular returns indicate either no conception or failure of maternal rec- ognition. In contrast, irregular returns imply successful concep-


Weaning-to-first-mating interval Parity 1 sows have prolonged weaning-to-first-mating intervals (WMI). Also, increased outside temperature increases WMI. The WMI varies depending on parity and season. As maximum temperature increased from 25 to 35°C, WMI in parity 1 sows increased by 0.8 days whereas in sows of parities 2 or higher, the increase in WMI was only 0.3 days. Parity 1 sows are three times more sensitive to high temperatures for WMI than gilts and sows in parity 2 or higher. This type of sensitivity in parity 1 sows appears to be related to their low feed intake during lac- tation. Like farrowing rate, low feed intake during lactation is a detrimental factor for WMI especially in parity 1 sows. Also, the weaning-to-first mating interval can be used as a pre- dictor for other types of reproductive performance. For exam- ple, sows with prolonged WMI will have lower farrowing rate and fewer pigs born alive. In addition, prolonged WMI is sug- gested to be related to a short duration of oestrus and a shorter interval between onset of oestrus and ovulation. A consequence of this is an increased risk of inseminating at a suboptimal peri- od, which can be a major cause of low farrowing rate and fewer pigs born alive.


Removal interval Removal interval accounts for 40% of non-productive days. Guidelines and actual culling intervals for mated sows and gilts are at least ten days higher in high-performing herds than in low- performing herds. Also, culling guidelines for mated sows and gilts are not strictly followed in any herd productivity group.


Pigs weaned per sow The number of pigs weaned depends on the pigs born alive and the pre-weaning mortality, as can be seen in Figure 1.


Pigs born alive (PBA) The PBA depends on total number of pigs born, stillborn piglets and mummies. Total number of pigs born varies depending on parity and season. For example, the highest PBA is in parity 3-5 which is about 10% higher than parity 1 sows. Also, as outside temperatures increase from 25 to 30°C, total numbers of pigs


PIG PROGRESS VOLUME 32, No. 6, 2016 7


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