The major causes of culling in a pig unit are many but according to recent field data and scientific literature, age related performance reduction, reproduction failure and lameness are the three major causes. An increased culling rate will result in decreased farm profitability through the inevitably high costs for replacement, as well as the lower number of pigs produced per sow per lifetime.
Sows are replaced in the herd either when the farmer strategically decides to remove a sow because she is too old (maximum parity approach) and as such less productive compared to a young gilt or when forced to do so as the sow is shown to be unproductive (low milk production, non return into heat, low number of piglets weaned etc) or she has locomotion problems.
Age related culling
Old age is often farmer subjective but normally covers old parities (e.g > 5th parity). As common practice, I usually advise pig farmers to consider their sows old enough to be culled when in their last farrowing they wean fewer piglets than the herd’s 1st parity sows average.
Reproductive failure is more closely associated with management factors and genetics. Sows culled for reproductive failure usually have a lower number of live born piglets, poorer mothering ability, more empty days and as such lower productivity which in turn makes them less profitable.
The third most important reason for premature culling is lameness. The term lameness is used to describe any deviation from normal locomotion and includes hoof and leg problems, poor movement, injuries and trauma.
Sows culled because of lameness -usually- are removed at a younger age and as such produce fewer litters and less slaughtered pigs in their life. Not surprisingly, recent data confirms that almost 50% of the removed sows due to lameness occur in the developing gilt phase and first parity sows. In these circumstances it is obvious that the economic significance of sow culling due to lameness is detrimental to overall farm profitability and any direct or indirect actions taken to minimize lameness through management and nutrition should be a priority in order to reduce overall production costs.
Before going any further, I should point out that some lesions that can cause lameness are not visible on external examination, while at the same time most available treatments are ineffective in commercial production systems. Therefore, the timely identification of lameness is critical, as well as understanding the real causes behind it and hence applying preventive measures.
Bearing in mind the above, the best way to identify lame animals is to observe them while focusing on a number of indicators such as:
- Off-Feed behavior & constipation
- Laying down to urinate, defecate or eat
- Poor body condition
- Hair loss on one side of the body
- Sliding while standing
- Excessive effort to stand or sit down
Putting aside any reference to primary and secondary infectious disease and housing -while accepting that both are critical in the incidence of lameness- I will focus on nutrition and how it influences lameness.
Tailor made feeding program for young breeding stock
Genetic improvements have increased sow potential productivity to nearly 35 piglets weaned per year and this obviously means much more pressure on the sow both in terms of weight carrying (more piglets equals more weight!) and milk production requirements (greater mobilization of calcium, phosphorus and other minerals from the bones to the blood stream to support milk production).
Modern gilts are great eaters and characterized by very high growth rate. While this characteristic is ideal for growing pigs it is not so for young, developing gilts where high growth rates negatively influence leg structure, longevity and life time performance.
To address this, a tailored gilt feeding program should be applied based on controlling feed intake and daily gain while optimizing gilt nutrition. This approach will ensure that young gilts will build a strong skeletal system ready to support 75+ pigs produced in their lifetime. A complete feeding program would include at least two and ideally three diets as a follow up from 50 Kg live weight to ensure proper gilt development. All these gilt diets should be fed at around 2.5 to 3.5 kg per head per day, depending upon desired growth rate, housing facilities, health, genetics and management conditions.
If, for practical on farm reasons, feed restriction is not an option then weight development should be very closely monitored and any necessary adjustments to dietary levels, based on daily intakes, are carried out in time to prevent over-developed gilts.
Calcium & Phosphorus
Calcium and phosphorus are the two most important factors influencing bone structure (size and width). Calcium is vital for the development and maintenance of the skeleton and provides strength. Phosphorus, on the other hand is essential for bone formation and skeleton mineralization.
Cereals and vegetable proteins contain significant amounts of absorbable calcium and phosphorus but the presence of phytate (which is a well proven ‘enemy’ of good nutrition as it acts as a major anti-nutrient) will reduce mineral (calcium, phosphorus, zinc, magnesium) bio-availability for bone mineralization. In this respect, increasing doses of phytase as a feed additive will speed up phytate break down and have beneficial effects.
In every case, make sure that the diet is adequate in calcium (aim for 7-7.5 gr/Kg) and phosphorus (aim for 3.5-4 gr/Kg available phosphorus) from limestone and monocalcium phosphate and use the extra phytase inclusion as an over the top application.
Magnesium is indirectly associated with calcium and phosphorus in the bones, as it is involved in the conversion of vitamin D to the active form 1,25 dihydroxy clolecalciferol which is necessary for Ca absorption. While it is well established that magnesium deficiency increases bone re-absorption, little work has been done on magnesium requirements for young breeding stock. Cereals and soybean meal are rich in magnesium and as such deficiencies are rather rarely experienced.
The main function of Vitamin D is the transportation, absorption and deposition of calcium and to a less extent of phosphorus. Before utilized, Vitamin D will be formatted to 1,25 dihydroxy clolecalciferol which is the active metabolite and controls calcium and phosphorus homeostasis by regulating Ca/P absorption and bone mineralization. Bearing in mind that Vitamin D3 is toxic at very high levels and at the same time insufficient supply will negatively affect calcium absorption and utilization, the suggested level is 1,200-2,000 IU/Kg of feed.
Biotin and claw lesions
Claw lesions play a significant role in sow lameness especially now days with group housed pens. Biotin is very important in the integrity of the hoof and can prevent cracked toes and certain foot trauma. The standard recommendation would be of 300 mg/ton of final feed but this could be increased up to 500 mg/ton if there is history of feet problems or inappropriate floors.
Microminerals constitute a small portion of the diet but their importance and contribution to bone structure and hoof health -especially in gilts and young parity sows- is undeniable.
Zinc is essential through its action to increase osteoblastic activity while suppressing osteoclastic bone re-absorption and building keratin proteins in hoof horn.
Copper is heavily involved in bone development, connective tissue and collagen production thus making the hoof stronger.
Manganese is necessary for bone formation and at the same time is critical for its role in proteoglycan synthesis which in turn is essential for joint cartilage formation.
Until recently, these trace minerals were generally added to sow diets as inorganic salts (because of their lower cost) but lately more and more field trials and scientific data support that chelated forms -designed to enhance absorption from the small intestine- are gaining ground in the industry due to their higher availability.
Given that mineral absorption might be limited because of antagonism with other feed elements, diets for breeding stock should be of a careful formulation while always bearing in mind that higher inclusion of inorganic forms does not guarantee an increased absorption and as such a better performance. In my formulations I use a targeted mixed supplementation of inorganic as well as organic minerals that combine effectiveness and economy and arrive at 100,50,15 mg/kg for zinc, manganese and copper respectively. And this has proved a very successful combination on the farms of our clients.