Photo: iStockphoto_Anatolii Tsekhmister
Gilts play a paramount role in farm profitability. Together with primiparous sows, they represent the biggest group in an inventory. Gilt development is directly linked to productivity performance in later life; they are the vehicles for injecting genetic progression on a farm. Here are six critical factors for successful gilt production.
1. Provide a dedicated unit
Producing gilts is different to producing fatteners. This is especially true today, when fewer farms purchase gilts and more grow them on farm. Gilts have different requirements in their management, nutrition and housing; dedicated accommodation, management and labor is required. This can be complicated when the number of gilts does not justify a separate unit. Pen space per gilt, floor type, and humanization (accustoming animals to human presence) are parameters with different requirements compared with fatteners.
Every production system must have a constant and adequate gilt pool according to needs and targets. The size of the gilt pool should cover the target replacement rate. In order to achieve an annual replacement rate of up to 50%, grandparent sow numbers should account for 8% to 10% of the inventory. Farrowing of the multiplication herd should be spread throughout the year so that eligible gilts are available for mating every week.
The first inspection of piglets should be carried out in the first days of life, during tagging. Piglets with abnormalities can be excluded at this point. The final selection should take place at around 100kg of weight. Selection should be carried out where there is enough light and sufficient space for the gilts to move freely. Attention should be paid to the number of functioning teats, growth, conformation and leg structure scores. One person should score every animal and all measurements must be recorded. Consider pool quality and requirements for the size of the next pool. Decide the selection density based on gilt batch quality, size of next pool and future insemination targets.
4. Puberty stimulation
Environmental factors such as mixing, boar exposure and other stressors trigger the onset of puberty by acting on the last part of puberty attainment. In order to have a more synchronized estrus in a pool of gilts, boar exposure should not start earlier than 140 to 150 days. The response of gilts to boar exposure could be an indication of fertility. If boar exposure is not enough to trigger the onset of heat in gilts, artificial techniques may be used, but these gilts are expected to be less productive, having a lower retention rate and a smaller first litter (Figure 1). One quarter of the gilt pool can be expected not to respond to boar stimulation, but part of this sub group should be retained as reserve gilts.
Figure 1. Retention rate for early, intermediate, late and non-responsive gilts following boar exposure over 12 non-negotiable aspects of gilt development
Direct boar contact is more effective than contact through a fence; fewer days are needed for the onset of estrus and estrus occurs in a better distribution (Figure 2). Light also plays an important role (Table 1).
Table 1. Effect of light on puberty onset age
Figure 2. Cumulative percentage of gilts attaining a puberty response to direct contact with vasectomized boar in either a purpose built boar stimulation area (orange), in gilt home pens (purple) or fence line contact (green)
5. Synchronized breeding and record keeping
Keeping records is the most important tool in gilt management. Once gilts are selected and boar exposure starts, the heat for individual gilts should be recorded. From these records, the next expected heat can be estimated. If the next heat is not regular, the gilt can be withdrawn from the pool as a gilt with an irregular cycle would result in a lower reproductive performance. For the regular cycling gilts, estimating the next heat 21 days in advance allows time for planning. Knowing which gilts are expected in heat facilitates decision making for insemination and grouping for flushing. In addition, synchronization costs may be avoided.
6. Insemination targets
By optimizing insemination targets, reproductive performance, sow longevity and overall profitability are optimized. However, the simultaneous achievement of optimal growth rate, optimal age and optimal gilt back fat depth at insemination is unlikely as these parameters are all interlinked.
Gilts with low growth rates need more days in feed to reach their target insemination weight, resulting in more non-productive days. Conversely, if the growth rate is too high, it could have a negative impact on longevity by causing future locomotive problems, and a negative impact on productivity through excessive body weight loss in the first lactation, resulting in a delayed return to estrus.
Reviewing insemination targets and research work carried out by various genetic companies indicates that insemination weight, with an optimum at 140 ± 5 kg, seems to be the first priority. Serving a second or third cycle would maximize ovary number and litter size at first farrowing. Following target recommendations based on herd genetics is the best strategy. Each genetic company shares mean parameters that optimize profitability according to their genetic line.
These above points do not cover all the parameters that should be considered in a gilt development plan. Issues such as acclimatization for incoming gilts, nutrition, nutrient requirements, feed quality and vaccination program (immunological preparation) are also important aspects. A sound gilt development plan can positively affect subsequent productivity and longevity of the sow, supporting farm profitability.