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One of the parameters used to analyze the reproductive efficiency of a farm is non-productive days (NPD). Its definition is well known: every day that a sow is not producing piglets, i.e., every day that a sow is not gestating or lactating. Although it isn't one of the most commonly analyzed parameters perhaps, one of the reasons it is very useful is because of its easy translation into economic data: we just have to multiply these NPDs by their unit cost, which currently can be around 3-3.5 €, to find the economic impact they are having on us.
Now, are we sure that all the days when a sow is not gestating or lactating are non-productive? Let's illustrate this question with two cases:
- Entry - first service interval. In many systems and management programs, non-productive days count from the time a gilt enters a farm (or from when she is selected if we raise our own replacements) until she is mated. But of course, what we are doing in that period is preparing the sow well (boar exposure and heat detection, controlling her growth and body condition, etc.), until the right time and conditions are met to mate her for the first time. Therefore, indirectly, we are working on a process that should be mandatory for the sow to produce piglets correctly during her productive life. So we should count only the days exceeding the established target age at first service as non-productive days.
- Weaning-first service interval. This situation is very similar, the non-productive days are calculated from the day of weaning, but the sow needs a minimum period of four days (with some exceptions) to trigger the whole hormonal process that leads to the expression of estrus and the ability to become pregnant again. Again, the sow is indirectly producing piglets during those days. After the fourth day, the days really would be non-productive.
Since these two intervals (entry - first service and weaning - day 4) are unavoidable and necessary for the sow to correctly fulfill her piglet production function, one could consider excluding them from the NPDs. For this, we propose a new concept, inefficient days. These would be the classic NPDs but exclude these two cases, and the name would be given because they would be the days in which a sow is not producing piglets due to some inefficiency (a return to estrus, a cull, a sow going into heat later than expected, an empty sow at farrowing, an abortion with a return to service, etc.), so it would be a more direct indicator to look at and analyze the reproductive problems of a farm.
We will illustrate this difference with a specific example. Using a typical farm with 550 productive sows and 3-week batch management, we will now compare the eight types of non-productive days (Koketsu et al, 2005) with the same types but with inefficient days, showing their corresponding intervals in days. Considering that the target age at first service is 240 days in this case, we see how the two intervals are clearly reduced, especially the one related to gilts before mating. Of course, the target age at first service (240 days in this example) should be determined by individual farm, based on the genetics used and the management system for replacement sows. And if a sow is mated before that target age but in the ideal conditions, she simply does not accumulate non-productive days.
Table 1. NPD intervals vs. inefficient day intervals (days)
NPDs
| Intervals | Days |
|---|---|
| Entry - first service | 152.5 |
| Entry - remove | 161.6 |
| Gilt first service - fertile service | 40.8 |
| Gilt first service to remove | 63.8 |
| Weaning - first service | 8.3 |
| Weaning - remove | 12.6 |
| Multiparous first service - fertile service | 55.0 |
| Multiparous first service to remove | 73.6 |
Inefficient days
| Intervals | Days |
|---|---|
| 240 days - first service | 18.0 |
| Entry - remove | 161.6 |
| Gilt first service - fertile service | 40.8 |
| Gilt first service - remove | 63.8 |
| 4 days post weaning - first service | 4.3 |
| Weaning - remove | 12.6 |
| Multiparous first service - fertile service | 55.0 |
| Multiparous first service - remove | 73.6 |
Below we group the eight types and translate these days into non-productive and inefficient days per sow per year, i.e. the average number of days a sow is non-productive or inefficient per year. We show the averages per sow present (since her entry into the farm) and per productive sow (since her first service).
Table 2. Average NPDs per sow per year versus inefficient days per sow per year (days)
| Sow present | Productive sow | |
|---|---|---|
| NPDs | 96.7 | 39.0 |
| Inefficient days | 43.8 | 32.2 |
The difference is very clear if we consider present sows, which is logical since for the inefficient days we excluded all the days from farm entry to 240 days. But it is also significant considering productive sows.
From this last table, we can affirm that each sow on the farm is not producing an average of 32.2 days per year due to various inefficiencies if we consider only productive sows, or 43.8 days if we also consider gilts that are mated after more than 240 days or are not ever mated.
In summary, we can state that inefficient days, since they exclude theoretically non-productive days that are actually unavoidable and during which the sow is indirectly producing piglets, would be a more accurate indicator to assess the impact of the different reproductive inefficiencies of the farm.
