Seasonal effects (temperature and light): analysis and minimization of their consequences

It is a widely documented fact that pig production has seasonal variations mainly focused on a descent in the reproductive efficiency in the gestation phase (difficulty in the coming into oestrus, a higher number of reproductive failures) during the summer and autumn months. These variations are due to two factors:

- High temperatures. These high temperatures have a double influence:

• They decrease the animals' compound feed intake, especially during the nursing stage. This causes that the animals have a worse body condition at weaning and later on during the mating.
• The animals suffer a thermal stress (the room temperature is over the thermoneutral temperature), and this makes it more difficult for the animal to trigger all the hormonal processes that cause the coming into heat and the maintenance of the pregnancy.

- Decreasing photoperiod: this is, the decrease in the number of daily daylight hours. The sow detects these variations in the number of daylight hours, and this causes, in the same way as the thermal stress, the interference with the hormonal mechanisms related with reproduction. This is an adaptative system of the animal in front of the conditions found in nature (in the same way as in the majority of wild animals, in which the reproductive functioning is reduced or stopped during autumn and winter).

Once this effect is known, in this article we are going to:

• Try to quantify it.
• See the consequences on production.
• Suggest handling strategies that minimize these consequences.

In order to do this we are going to use data from year 2008 in a group of 72 farms obtained from PigCHAMP Pro Europa's database.

Quantification of the seasonal effects

Graph 1.- Variations in the interval from the weaning to the first mating and in the farrowing rate resulting from the matings according to the month, year 2008.

The percentage of births belongs the fertility of the farrowings resulting from the matings carried out during the period, and not to the births that happened during the period.

We can clearly see how, during the summer and early autumn months, the sows find it more difficult to come into heat after the weaning and to maintain their gestation.

In the interval from the weaning to the first mating what increases is the percentage of sows that are mated more than 5 days after the weaning, as it can be seen in the following table:

Table 1.- Range of intervals from the weaning to the first mating, year 2008

In the losses during the pregnancy (Table 2), the increases are due to the percentage of repeat oestruses, and especially to the percentage of miscarriages, that would increase a 70% (in fact, this decrease in the efficiency is sometimes also called "autumnal miscarriages syndrome").

Table 2.- Analysis of the losses during the gestation according to their cause, year 2008

Consequences of the seasonal effects

These seasonal variations in the efficiency have two effects:

• Decrease of the global annual productivity of the farm because the decrease in the efficiency during this period has a negative influence on the annual averages.
• Variations of the productive paces in the farm. A common effect in many farms is as follows: during those months, as well as during the rest of the year, the same number of sows is mated for each period of time. Due to the lower farrowing rate, the average of farrowings and, consequently, the number of weanings at the end of the year-the beginning of the following year are lower. In a farrrow-to-finish farm, the piglets that are born during this period are the ones sent to the abattoir in summer (when the price of pork is normally higher), so there is a deficit of sales of animals during the period in which their selling is more profitable.

Minimization of the seasonal effects

The first thing that must be borne in mind is that the data in this article are averages from a group of farms, so in each individual farm it is necessary to analyze the moment of the start and the end of the seasonal effect (it is not the same a farm in Andalusia [South of Spain], in which the heat will be a more important factor (so the seasonal effect will probably appear earlier) than a farm in Castilla y León [middle North of Spain], in which the decreasing photoperiod is the dominant factor) as well as the quantification of the mentioned effect (making a historical study of the data of the farm).

There are two strategies for the minimization of the effects:

- Productive: aimed at the reduction of the impact of the heat (coolings; refrigeration of the rooms, especially the farrowing quarters, constant access to fresh and good quality water...) and of the decreasing photoperiod (installation of timers in the lighting of the buildings in order to maintain a minimum of 14 daily hours of "daylight") on the animals. These strategies can minimize, but not eliminate, the seasonal effect.
- Handling: A quite profitable strategy consists in increasing the number of matings/period from the moment in which this seasonal effect appears (be careful: not when the number of returns to oestrus and miscarriages start to happen, but 3 weeks-1 month before). The mentioned increase can be of a 5-10%, and it is going to favour a sufficient number of weanings at the end of the year-the beginning of the following year and, consequently, a higher number of pigs to be sold in the most convenient moment. It is also important to end these "excessive matings" when the seasonal effect is over because if not, we run the risk of having more pigs to be sent to the abattoir in autumn-the beginning of winter, with already low prices.