The object parameters of replacement management should be:
- a replacement rate < 50%, at least in the best herds.Unfortunately this is not the reality in many herds so that there are often replacement rates of over 55-60%, with the subsequent spiral of poor consequences.
- beginning of puberty at 26-28 weeks.
- average age at first mating between 30-34 weeks.
- a maximum of 5-6% of primiparous sows that don’t reach estrus at 32 weeks
- farrowing rate of 85-90% with 12 pigs born alive in the first parity.
- an average productive life of 4 cycles.
The distinct strategies must bear in mind the key physiological characteristics of the current genetic lines, which due to selection by lean content in the final product, have a greater body size and fewer fat reserves. Many of the habitual recommendations and practices were established 20 years ago when genetic lines had more fat. Therefore, they don’t take account of the metabolic changes associated with a lean deposition and greater fat reserves in the current lines. Some traditional recommendations, especially those to do with fat, are not currently feasible and therefore are no longer valid.
The dietary strategy for replacement sows aims to have optimum values of weight, age and reserves (lean: fat) at the time of the first mating. During gestation the objective is for the sow to complete her maternal growth, basically lean tissue, and to arrive to the first parturition with a good body condition to begin the first lactation. It is extremely difficult to correct or compensate for any deficiencies or excesses of reserves once the nulliparous sow has entered the productive process. Although the sows from current lean lines tolerate better the losses of body protein to produce milk, it is vital that the ingestion of energy and nutrients is at a maximum during the first lactation. An excessive catabolic state has disastrous effects on the productivity of the second cycle, the reproductive future and longevity. Good productive results and a good body condition of the primiparous sow at the moment of the first weaning are practically a guarantee for productivity and rentability of the breeding herds.
It is extremely difficult, if not to say mistaken, to make recommendations that are valid for all conditions. The response depends on the combination of the genetic line, the type of installations, the management of the animals and the feeding programme of each farm. The correct approach is to establish objective values of the control factors (weight, age, loin depth and fat thickness) and from the results obtained in the herd to modify the dietary and nutritional levels with the aim of getting the results to be as close to the objective values as possible.
Current recommendations for the optimum conditions of sows at the time of first mating. In order of importance:
|Weight (high lean content)
|Number of estrus
||Average = 230 d (Range= 190-260 d)|
|ADG from birth to mating
|Backfat (P2)||15-17 mm|
In Denmark, a radically distinct approach to the replacement strategy is recommended. In the Danish system for primiparous sows, they recommend the nulliparous sow should mate at liveweight of +160kg and age of 9 months (+270 d), possibly in her 4th or 5th estrus. In this way, a replacement with significant reserves and a primiparous sow that is very resistant to the stress of lactation is achieved, so that the size of the first, and possibly the second litter is increased. In contrast, the number of non-productive days before first parturition is increased.
In short, the economic rentability of each replacement strategy should be evaluated while keeping in mind the starting situation, the genetic type, the costs and the improvements obtained in productivity. Depending on the specific herd characteristics the stratagies to follow should be adapted or modified.