Mixing sows for group housing
This important skill must be learned, in countries that previously have put their pregnant sows in individual stalls
It has been quite a year for sow housing methods in North America. The starting point was the announcement by Smithfield Foods that it would adopt a policy of phasing out individual gestation stalls over a period of 10 years. Soon after, a similar course of action was announced by Maple Leaf in Canada. Then the US states of Florida, Arizona and Oregon had electoral votes that, in effect, banned the use of the single-sow stalls or crates.
More recent events have included a decision by members of the Colorado Pork Producers' Council also to stop using gestation crates, which was said to be in response to public concerns and changing market conditions. In addition, major fast-food companies such as McDonalds and Burger King have indicated they would use pork only from units whose sows were not housed in gestation stalls during pregnancy.
Crates at a crossroads
Single stalls or crates therefore seem to have reached a crossroads in their long history. First developed on a commercial scale in the Scandinavian countries in the 1950's, they spread to the UK and other European countries in the early 1960's before entering widespread use in the USA. Until the end of the last century they represented the system of choice for gestation housing, especially in large confinement units.
Their imminent demise in Europe and North America has come about because of pressure from animal welfare lobbyists, public opinion and widespread attention in the mass media. Consumers have also been influenced in the marketplace by the growth of niche marketing of meat produced under welfare-friendly conditions. Gestation stalls and tethers were banned in the UK as long ago as 1999. The other European Union countries will outlaw stalls by the year 2013.
So it seems the pork production business internationally must find alternative ways of housing its sows during gestation. In the USA, this has posed a problem for producers due to the shortage of scientific information about the various choices available. For an industry that has developed without knowledge of the management of group systems, it is also difficult that these demand more skilled husbandry than was necessary for managing sows in individual stalls.
Discussions in North America over the last year have rotated around some general points for and against each system, but without reference to the all-important issue of how to manage the mixing of sows into a group. The whole exercise of group formation and maintenance presents a formidable challenge to the herd manager because of the considerable aggression shown by sows to each other as they sort out dominance and establish a peck order.
Fighting at mixing can lead to body scratches, torn ears and even (in severe cases) to severe wounds and broken limbs. Udders and teats can be damaged when they are swollen and vulnerable and some sows can be deprived of feed and water. Not exactly a welfare-friendly situation!
Rules show the right time
As the first practical question to consider, when do we mix them? There are a few rules on mixing and one of them states the general agreement that it should be done either immediately after weaning or after embryo implantation has occurred — which means in practical terms 26 to 28 days after the sows were weaned. A routine of post-implantation grouping allows pregnancy checks to be performed before the sows are mixed.
Early morning is the ideal time for mixing them as it leaves more opportunity for observation during the working day. I recommend giving them access to full feed and water at this time. Experience shows, too, that sows for mixing should be sorted by size and parity while also taking their body condition into consideration. Age of weaning is also another factor. The trend towards later weaning at 28 days means peak milk production has passed and udders may be less tender and swollen.
Mixing should take place on neutral territory, free of obstructions if possible, and preferably on a solid floor rather than slats. It is probably too much to ask herds in the USA to provide straw bedding or corn stalks across the floor of the mixing pen, but a few strategically-placed large bales will offer some privacy and a convenient escape area for the members of a newly-formed large group.
Actions against aggression
Sedatives have been tried on occasions to reduce aggression, but not with any great success. Doses are sensitive to weight of sow, site of injection and fat-cover. Although they may calm her when first applied, the sow is likely to resume aggressive behaviour and antagonistic interactions on her recovery a few hours later.
Other managers have sprayed a strong-smelling disinfectant or deodorant on sows before mixing, to act as a masking agent. Years ago I used a colourless mineral oil (liquid paraffin) on the backs of the sows. This made the sow slippery and more difficult for others in the group to grip, as well as helping to soothe bites and scratches.
The presence of a boar as a so-called 'policeman' can certainly help, this job usually going to a vasectomised boar.
Let us say we have mixed sows into a group, they have farrowed and they are about to be regrouped for the next parity in gestation. At this stage it would be useful if the same animals could be kept together for another round.
In my experience this familiarity means less fighting among sows mixed at weaning time. Unfortunately, however, another consequence of the practice is that group size cannot be retained because of the need to replace some members. Replacement rates of approximately 40% are quite common, with culling for poor reproductive performance, parity profile and health reasons. At the final analysis we must accept that some mixing of sows will be essential in order to arrive at the appropriate group size.
The difficulties of maintaining groups for gestation across multiple parities can be resolved by management, but perhaps there are also other possibilities. For example, is it time to reconsider once-bred gilts in this context? Young gilts could be selected and mixed at weaning, when any fighting among them would not be a major problem. Further selection could be made at 70kg and 115kg liveweight — when they would still be considered market pigs if rejected for breeding purposes. The selected gilts would be housed in groups throughout gestation, farrowed and then sold into the meat market as soon as their litter had been weaned. PIGI