August 23, 2010

Research probes on weight variation among pigs

Being a major challenge for pig producers, UK research continues to investigate ways to both reduce and manage the variable weight of pigs.

At the Agri-Food and Biosciences Institute (AFBI), Hillsborough, pigs have been weighed individually for many years and as such a very large set of data has been compiled. With funding from Devenish Nutrition Ltd, it was possible to interrogate this data set with the aim of achieving a better understanding of factors that could reduce the variable weight of pigs.

Grouping pigs in uniform weight or mixed weight groups at the start of the weaning or finishing period has been investigated in a number of studies but results have not always been the same. Over the last number of years, pigs on the AFBI Hillsborough herd have been penned in groups which represent a range of 'variation'. For example, at weaning, in some pens the weights of all pigs were within a two-kg range whilst in other pens the weight of pigs spanned an 8 kg range.

In total 391 pens of post weaned pigs were examined. It was found that when the initial weight range within the group was very low (under approximately three kilogrammes), by the time pigs were approximately 30 kg and ready to move to finishing accommodation, the range in weights within the pen increased to a greater degree than if the weight of pigs in the group had initially spanned a large weight range (over approximately five kilogrammes). Other researchers have found similar results and have suggested that if a degree of variation in weight within a pen of pigs is not present when pigs are initially grouped, it will develop over time. This suggests that placing pigs of similar weight within a pen at weaning will not reduce the variable weight of pigs within that pen when they are due to be transferred to the finishing accommodation. The current study would suggest that at least a 5 kg spread in weight of pigs in the pen at weaning is needed to minimise the expansion in weight range by the time pigs are ready for transfer.

In the AFBI data set, the birth and wean weights of 13,158 pigs from 1,344 sows across 96 farrowings (January 2003 to April 2008) were examined. All pigs were weaned at 28 days of age (+/- 2 days) and managed similarly between birth and weaning. As expected, as birth weight increased, so did wean weight. In addition, the wean weight of pigs with low birth weight (under one kilogramme) was found to be more variable than that of pigs with a birth weight over one kilogramme and as birth weight increased to two kilogrammes variation in wean weight continued to decrease.