There are a lot of studies, opinions and articles on when gilts should be bred for optimum lifetime productivity. So what is the correct answer? We believe it depends on how intensively you manage your gilt development process. Even though the average annual replacement rate of females is in the range of 45-50%, many operations still pay little attention to gilt development until they can’t meet their breed targets. In this article, we want to focus on the key aspects of gilt development.
There are five areas that require focus:
• Correct boar exposure
• Weight at first boar exposure
• Age at first boar exposure
• Which estrus to breed gilts on
• Body condition
In a previous newsletter (May 2009), Dr. Don Levis described effective boar exposure. He stated that research has shown that boars must be a minimum of 10 months old to effectively stimulate puberty onset in gilts. Five to ten minutes per pen of 15 gilts per day of physical boar exposure should be adequate to stimulate puberty. Only boars with a high level of sexual behavior should be used and they should be rotated to prevent fatigue and disinterest. Many farms tend to use the boar that is easiest to move, which may not be your best heat check boar. Research is also clear that the boars need to be housed away from the gilts, preferably in a different air space, to prevent continuous boar exposure. Continuous boar exposure will make gilts less likely to exhibit estrus quickly. Instead, it may require exposure for as much as 20 minutes to get a standing estrus response.
The weight and age at first boar exposure are inter-related. If gilt growth rate is depressed due to disease, overcrowding, or inadequate nutrition, they will not reach puberty until they are older. If gilts have adequate growth, they can still be stimulated at too young of an age. Research has shown that puberty is attained more rapidly and with greater synchrony when first boar exposure starts at later ages. However, you also need to take into account the increased feedcosts required to take gilts to older ages and heavier weights before they enter the herd.
Shows results from a commercial production system. Gilts were either weighed or weight was estimated with a flank-flank body measurement at 24 weeks of age. The goal was to identify gilts that should reach a body weight of 300 lbs at 27 weeks of age. Gilts that met both the age and weight criteria were then moved to an estrus zone, where boar exposure was taking place. If they did not meet either requirement, they were left in the gilt developer. After one recorded heat, the gilts were moved to the breeding row for breeding on the subsequent estrus. The gilts bred early were very productive.
Shows results from a different commercial farm, where growth was more limited by disease and overcrowding.
Notice that there is a much different pattern based on how they flow gilts into their system and how the farm is set-up. In their system, 221-230 day old gilts were the most productive.
A large amount of research has been performed to study the effect of breeding gilts on their pubertal estrus or waiting to breed on the second or third observed estrus. The data is very clear that skipping the pubertal estrus and breeding on a subsequent estrus has a positive effect on productivity. Notice that regardless of age at pubertal estrus, waiting to breed on a subsequent estrus improved productivity.
Lastly, gilt body condition at breeding and at farrowing has a profound impact on lifetime productivity. Gilts need to be in a positive energy balance, i.e., gaining weight, during the breeding phase and up to the first positive pregnancy check. This will result in better conception rates and higher total born. Gilts are continuing to grow, so they have higher maintenance requirements than gestating sows. However, gilts that are over conditioned have a greater tendency to give birth to stillborn pigs and will eat less during lactation. This will result in the gilts being in a negative energy balance at weaning time, producing longer wean-estrus intervals and lower subsequent total born, when compared to those gilts in a positive energy balance at weaning.
Gilt litters can represent 20-30% of all litters every year. And improving gilt productivity at the first parity often results in improved lifetime productivity. An intense focus is needed on gilt development in order to achieve high productivity in a sow system. Each individual system will need to identify the growth rate and age of its gilts, so that they can breed them at the appropriate time. The health status and acclimatization period must also be taken into account. Implementation and execution of proper gilt development sets the stage for superior lifetime performance.