Protection using PCV2 lifts growth rates
Since the later months of 2006, a vaccine for piglets to protect them against the effects of porcine circovirus type 2 (PCV2) has been widely and effectively used both in the USA and in Canada. Documenting piglet survival rates was the most obvious goal of vaccine users because mortality is a pronounced feature of PCV2 disease. But many producers reported that surviving pigs in outbreaks with severe mortality often had acceptable growth rates. Interestingly and somewhat unexpected, there were even reports that the rate of growth had improved.
With subsequent interest in measuring and evaluating the impact of vaccination on weight gains and efficiency, several studies have since shown growth benefits from vaccine use. The financial implications of vaccinating have also been addressed. One controlled study reported last year estimated the lower mortality due to vaccination to be worth US$3.32 per pig, with the improved sale price for the animals adding another US$4.21 so that the economic benefit from the use of the vaccine worked out at US$7.53 per vaccinated pig.
Conducted as part of an evaluation of the use of the Intervet PCV2 vaccine with regard to both mortality and growth performance, this study took place at a farrow-to-finish operation of 1700 sows in the American Midwest. This herd had experienced a mild increase in mortality rates and a severe increase in culling, mainly involving castrates rather than gilts, due to PCV-associated disease. Along with PCV2, the unit was also known to be infected endemically with a variety of pathogens including Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae (App), swine influenza virus, PRRSv, atrophic rhinitis and Lawsonia intracellularis. Due to these disease challenges, in fact, the herd was in the process of depopulating.
The pigs used for the study were from 2 consecutive weekly weaning groups. After weaning at approximately 23 days of age, they were allocated randomly to vaccinated or control groups with stratification by start weight, gender and litter of origin. Vaccinated and control pigs were housed together in the same pens within 4 nursery rooms and then 4 finisher rooms.
Their weights were measured when weaned and at the end of the nursery phase, then approximately 6 weeks after entering the finisher (grower phase) and about 6 weeks later (finisher phase), which was 2 weeks before the first of them were shipped to market. The weight data allowed a calculation of daily gain values for each production phase. The daily gain during the finisher phase and the final finisher weight were used to predict the expected market weight with a maximum value of 280 pounds (127 kilograms).
The presence of PCV2 and PCV-associated disease was confirmed by serology and virus identification and the presence of lesions in tissue samples. Among the control pigs there were 30 out of 32 found to be seropositive at 3 weeks old, 25 out of 28 at 6 weeks, 13 out of 28 at 9 weeks, 5 out of 28 at 12 weeks, 19 out of 28 at 15 weeks and 27 out of 28 at 21 weeks. The overall health status of the pigs was similar to previous groups, although 2 moderate outbreaks of App occurred during the study in one room in the grower phase and one room in the finisher phase. The rate of App mortality was similar among the vaccinated and control groups.
Both mortality and growth rates were improved by vaccination. The greatest difference in growth rate occurred during the grower phase. Cull rates were 7.5% for vaccinates and 11.0% for controls; this difference was not statistically significant.
The effectiveness of the vaccine with regard to mortality has been well documented. But the data in the Tables clearly show the benefit of vaccination with regard to growth performance as measured by daily gain and final market weight. With the reduced mortality and extra sale value estimated to be worth $7.53, the net benefit to the user was predicted as approximately US$5.90 per pig.