The effect of cross fostering on PRRS transmission and litter performance

Abstract Text:

Cross fostering is used in swine production to improve growth performance and reduce mortality; however it is unknown how much cross-fostering transfers PRRS. Therefore, the objective of this trial is to determine the effects of cross-fostering programs on transmission of PRRS, piglet growth, and pre-wean mortality (PWM). On a commercial sow herd, 235 multiparous (1-5) sows, 10 weeks post-LVI from an acute PRRS break, were utilized. Four cross-fostering treatments were applied prior to farrowing:  A) no movement of piglets, B) movement at 24 hours, C) movement at 5 days, and D) movement at 10 days. Litters were assigned a treatment at birth and randomized throughout the room and the litter received no new piglets. Corresponding to treatment, the 4 heaviest pigs were moved (excluding treatment A). Litters that received the fostered pigs farrowed on the same day, same room, and same treatment. Eight tagged pigs/litter were tested for PRRS by PCR at birth and weaning. Litter birth and wean weights were recorded. Performance data were analyzed using Proc GLM by SPSS with litter as the experimental unit and PRRS transmission data was analyzed using Proc GLIMMIX in SAS with piglet as the experimental unit. Cross fostering pigs at 10 days of age produced an elevation in the prevalence of PRRS, with an increase of 8.8% in positive pigs at weaning (P < 0.01).  Other treatments showed no significant difference in PRRS transmission (P > 0.10; Table 1).   No difference between treatments in ADG and PWM (P> 0.10). Cross- fostering at 10 days of age at 10 weeks following LVI enhanced the spread of PRRS. Results confirm restricted cross fostering programs should be implemented to reduce PRRS transmission even after 10 weeks post PRRS intervention.

Table 1. Effect of cross-fostering programs on PRRS transmission

	Cross-foster treatment
Values	None	24 h	5 d	10 d	SE	P-value
Pigs blood tested	454	503	488	479
PRRS positive at birth, %	0.1	0.8	0.8	0.1	0.400	0.9999
PRRS positive at wean, %	4.3b	3.2b	2.2b	8.9a	0.800	<0.001
Increased PRRS positive*, %	4.2b	2.4b,c	1.4c	8.8a	1.000	<0.001
a-c within a row differ indicate P< 0.05 *The mean represented as “Increased PRRS Positive” was generated by (PRRS positive at weaning - PRRS positive at birth = Increased PRRS positive)

Keywords: cross fostering; PRRS transmission; Pre-wean mortality