All agree that during the time pigs are infected and sick that performance is reduced. The interesting part is what happens after the pigs recover from infection. As one talks to producers and others there are various opinions on what happens to growth performance after pigs recover from a disease challenge such as PRRS virus. These opinions, in many cases are based on personal experience, which shapes the thinking of most of us.
Some have suggested that the pigs increase their performance above normal and compensate for the reduced performance during sickness. Others have suggested that the recovered pigs increase their performance but not above what one would expect if the pigs had not been sick. Finally, some suggest that recovered pigs never regain “normal” performance and fall further behind where they would have been if they had not been sick.
Some interesting work has been conducted in this area and was reported as part of presentations at recent conferences. Groups of two littermate pigs were split into two barns after the nursery period and had ad libitum access to a standard corn-soybean meal diet and free access to water. At week 0, (72 - 75lbs body weight) gilts in one barn were inoculated with a field strain of PRRSV (PRRSV+) and gilts in the other barn were injected with a saline solution (PRRSV-). PRRSV+ gilts were all confirmed PRRSV positive and all PRRSV- gilts remained so throughout the study. No mortalities or other infections were reported in the study. Pen feed intake and body weights were recorded weekly and the trial was completed at an average body weight of approximately 285lbs. More details on the study can be found in Gabler et al. (2013).
The PRRSV+ animals took 14 days longer (119 vs 105) to reach the final body weight. Over the complete feeding period average daily feed intake and average daily gain were 6 and 10% lower, respectively and feed conversion was 7% poorer for the PRRSV+ pigs compared to the PRRSV- pigs (Gabler 2015). What is interesting is shown in Figure 1. Notice that for all three measures there were significant reductions during the 4-week period after inoculation. Clearly PRRSV had a significant impact. However, from week 5 until the end of the trial there were no significant performance differences between PRRSV+ and PRRSV- pigs. So the PRRSV+ pigs did not perform poorer nor did they compensate for their reduced performance. Their performance increased to “normal”, not different from the PRRSV- pigs.
The next obvious question is - did the reduction in growth rate have a different effect on the main components of growth rate, namely fat and protein deposition? After the first 80 days of feeding, the PRRSV+ pigs had estimated protein and fat deposition rates that were 15% and 20% lower, respectively compared to the PRRSV- pigs. Thus, both fat and lean deposition rates were negatively affected by similar amounts in the face of a PRRSV challenge.
So what does this all mean? Assuming the impact of most diseases is similar to what has been shown for PRRSV then a focus on enhancing the pig’s performance while it is exposed to a disease makes sense. Once the pigs fought off the disease they went back to their previous potential, although in this case the overall impact of the disease is clearly seen in terms of lost performance. So, we need pigs that exhibit a reduced impact of disease on feed intake, growth rate and feed conversion while they are “fighting” the disease challenge. This leads us to the idea of increasing a pig’s disease resilience. This is a pig that has an ability to mount an effective and appropriate immune response, reduced impact on performance and will recover sooner getting back to normal production. This is the area of opportunity that is being explored in new work on resilience – not all pigs behave in the same way, and there can be significant variation in disease impact as well as the time to recover.
Genesus Inc. has invested significantly in health research and is currently participating in projects focusing on improving disease resilience in both sows and grow-finish pigs. Improving disease resilience will contribute positively to the profitability of our customers.
Figure 1. Effect of PRRSV on weekly performance (from Gabler 2015).