IT STARTS FROM GILTS
For a gilt to be able to have a long productive life, she needs to be prepared well prior to entering the breeding herd. The objectives for growing a gilt is quite different from the objective for growing a finishing pig. The aim is for the gilt to hit the targeted weight, age, back fat and estrous simultaneously for optimal results.
Ideal live weight between 135-145kg at first mating
Ideal age at first mating 30-34 weeks of age
Ideal back fat at first mating (15-22mm but higher end is better)
The table below is illustrating the correlation between the live weight of the gilt at the first mating and the future prolificity. The difference appears from the second parity. The gilts that have not been well prepared show less number of total piglets born, either because they produce smaller litter (they may have smaller uterine capacity) or because they experienced less parity (premature culling).
To get to these targets, we need to ensure a growth rate from 60 kg to first mating of 600-700gm/day. Any female that grows slower than 550gm/day or faster than 800gm/day should be removed from the group and sold as a slaughter pig. If the gilt is growing below 550gm/day, it would imply she likely has underlying health challenges and will not be the best mother going forward.
The gilt keeps on growing and develop herself until the second parity, especially the uterus and mammary organs. If we impair her development at any stage before second farrowing, that could have negative consequences on her future reproductive performance. That means that during the first two parities, the nutrition program needs to cover sufficient nutrients for her own body growth as well as the first litter. The gilt will always give preference to the litter. So, if there are some nutritional deficiencies, her own development will be negatively impacted which will result in future reduction of her reproductive performance.
We should, therefore, carefully monitor the gilt weight during the first reproductive cycle. It is best to feed developing gilts ad libitum to avoid any disruption to mammary and structural development. We need to measure the growth rates and adjust diet density according to changes in their appetites as their metabolism slows down and their appetites rise (around 100kg live weight).
The lower appetite of lactating gilts can be partially overcome by increasing diet density using a lactating gilt diet or by offering a top dress (fish meal/Full fat soybean is a popular option). We can increase as well the feeding frequency to a minimum of 3 meals per day.
Gilts digestive tract is not as mature as it is for adult sow. Their stomach is smaller and the fermentation capacity of their colon is reduced. Therefore, they will process fiber less effectively than adult sow and it maybe necessary to offer a specific diet for gilt development with lower fibre level.
Gilts are very much exposed to oxidative stress because they need to cope with their body growth together with the development of the mammary glands. Dietary anti-oxidants could help to reduce this stress and should contribute to increase feed intake. Field experimentations demonstrated as well that the addition of 0.5% of plasma protein promote higher feed intake through its anti-inflammatory properties.
Finally, to limit the loss of weight during its first parity, we may consider reducing the weaning age slightly by 3 to 4 days for all or half of the piglets. That strategy could limit pressure on the gilt during her first lactation and help her to finish her development and get prepared for the second parity.
Regarding her bone structure, nutritionists must pay a special attention avoid future problems of lameness that would lead to premature culling (represents up to 50% of total premature culling). Mineral depletion occurs in sows over time as the intake of minerals (and vitamins) per kg of live weight declines with parity (age). We are recommending to use a breeder premix from 60kg live weight to ensure the gilt has time to maximise her mineral and vitamin status to ensure that structural soundness, oxidative status and fertility are optimised.
It is therefore critical to get the gilts to store as much calcium as possible in her bones before entering in reproduction as she will keep on loosing calcium during all her life. The Total calcium / available phosphorous ratio for optimal bone mineralisation is quite different to the ratio for optimal growth performance. Gilt developer diets should be formulated to a ratio of 1.9-2.1 total calcium / available phosphorous including the matrix uplifts from phytase. (e.g. total calcium of 0.85% and available P of 0.42%).
But even with such ratio and given the low bioavailability of calcium carbonate (only 30 to 50%), this strategy may not be sufficient to build up sufficient reserves in the bones. Increasing the level of calcium carbonate is even counterproductive. Indeed, a too high calcium level will impair the absorption of phosphorus (because of a chelation of Calcium to Phosphorus and Phytase) . Moreover, carbonate has a very high acid binding capacity and will lead to increase pH in the stomach and lower effectiveness of digestive enzymes. Therefore, the recommended strategy to improve calcium absorption is to use highly bioavailable source or to use precursor of arginine. This amino-acid is needed in the enterocytes to produce CaBP (calcium binding protein) that are the transporters in charge of exporting calcium from the enterocytes to the blood.
Next month, we will discuss about nutritional strategies to increase sow longevity.