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Diet deliberations: Higher-spec diets can boost performance of immunocastrated pigs

By Joris Van den Heuvel, DVM, Business Manager, Zoetis

Today, a growing number of male pigs in Belgium receive a vaccine that reduces boar taint, without having to physically castrate. As the number of vaccinated pigs continues to rise, we get a lot of questions about their unique nutritional requirements.

Previously, nutritionists recommended feeding these vaccinated, or immunocastrated (IC), pigs diets similar to those offered to gilts. However, new research shows that adjusting diet specifications could help IC pigs access more of their inherent genetic potential for fast, efficient growth, without compromising meat quality.

A recent study indicates that feeding IC pigs a higher-lysine diet during early production (from 20 to 80 kg live weight) can boost performance at this stage, with subsequent benefits seen in performance throughout the entire finishing period. With these nutritional specifications, the data show that IC pigs can perform up to 15% better than their physically castrated counterparts, as measured by average daily growth (ADG) and feed conversion efficiency (FCE). (Table 1.)Layout 1

Similar findings are also being reported in the field. Experience on Belgian pig farms over the past five years shows that feeding IC pigs a high-protein diet allows the typical Belgian breed to express more of its genetic potential for fast, lean, efficient growth. By adjusting feed specifications, many producers have discovered that additional lysine yields better ADG and improved FCE. By comparison, feeding a gilt diet to IC pigs tends to compromise their performance at this stage and reduce profitability.

Practical pointers

For comparison, let’s assume a Belgian gilt diet has been formulated with 100% of the lysine requirement to reach target performance. Research suggests that physically castrated males would need only 98% of that lysine level in their first- and second-stage feeds and only 94% in the final-stage diet to achieve the same level of production. At the other extreme, entire boars would need a higher lysine inclusion in their diets to fuel growth potential, requiring 105% lysine in the first stage, 108% in the second stage and 114% in the final stage.

The nutritional needs of IC pigs fall somewhere in between. During the first and second stages, they should be fed a diet similar to that of entire boars, with higher lysine inclusions of 105% and 108%, respectively. For the finishing stage, however, the diet should have a lower lysine content — similar to that used for surgical castrates — to optimize growth, but avoid excessive fat deposition and grading penalties.

Minerals matter

Although protein requirements are of primary importance when feeding IC pigs, producers and nutritionists should also consider other dietary factors that can affect productivity, performance and welfare. Evaluating the mineral content of diets fed to IC pigs is worthwhile, as the physiological changes associated with hormone suppression in maturing male pigs can influence how certain minerals are metabolized.

Studies show that for every kilogram of lean protein deposited, pigs retain between 34 to 39 grams of phosphorus. Any increase in lean-tissue growth would therefore alter the metabolic demand for this mineral. Research confirms that IC pigs have higher phosphorous requirements than their physically castrated counterparts, due to their greater capacity for lean, efficient growth. Therefore, producers rearing IC pigs should consider the levels of phosphorus in their finishing feeds — particularly if they choose to adjust diets to access more of the pigs’ growth potential.

Feed intake

IC pigs have much higher feed intake than physically castrated males, particularly in the latter stages of the finishing period. Following a 14-day transition period after the second boar-taint vaccination, which is usually given 4 to 5 weeks before slaughter, feed intake rises rapidly. In fact, studies have shown that IC pigs may consume up to 40% more than they did before vaccination.

Producers must learn to manage this increased appetite, as the economics of higher feed consumption at this stage can significantly affect cost of production, efficiency and carcass quality, as well as economic returns. However, many producers in Belgium have found that a less expensive diet can be used in these pigs during the final stage of growth (80 kg live weight to slaughter). When combined with high-specification diets in the first and second stages, the result is lower feed costs and, ultimately, an improvement in margin per pig sold.


As with all pigs, practical and welfare considerations are also critical to optimizing the performance of IC pigs and return on feed investment. Feeder space, feed availability and water supplies must be sufficient to prevent stress and ensure that pigs have easy and adequate access to food and water.

Potential inefficiencies in the production system should also be identified. For example, experience on Belgian farms shows that regularly monitoring feeding strategies helps producers optimize feed use and minimize inefficient weight gain. Keeping a close eye on nutrition, in relation to pig growth and performance, helps control production costs and maximize revenue potential from the whole herd, not just IC pigs.

More than a castration alternative

The Belgian experience with boar taint vaccine over the past five years confirms that with proper nutrition at each stage of growth, IC pigs can yield lean, meaty carcasses of a consistent quality, with high levels of marbling in high-value cuts. These factors are economically relevant and clearly demonstrate that using this vaccine offers pig producers much more than just an alternative to surgical castration. The production and carcass-quality benefits of boar taint vaccination, combined with the welfare advantages and potential cost savings it offers, mean pig producers choosing this option are well placed to satisfy the discerning demands of a more welfare-oriented, efficiency-driven supply chain.

Download Technical Bulletin.



Technical Bulletin: 2014 Nutritional Guidelines for Immunologically Castrated Male Pigs, Zoetis Inc.



Diet deliberations: Higher-spec diets can boost performance of immunocastrated pigs
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