Relationship between Neospora caninum and early pregancy losses in dairy cow

Relación entre Neospora caninum y el aborto temprano en vacas lecheras

Abstract

Introduction: The fertility of high-producing lactating dairy cows has decreased during the last decades. Pregnancy losses in dairy cows are an important aspect of infertility leading to poor economic performance. Late embryo losses (LEL) are assumed to be of multifactorial origin, being N. caninum infection one potential cause.

Objective: The objective was to evaluate the association of N. caninum infection with LEL in grazing dairy cows.

Material and Methods: A case-control study was carried out in a commercial dairy herd (32°49´ S, 62°52´ W, Argentina) where Hosltein cows (n=92) were enrolled. Pregnancy was diagnosed by ultrasonography at 30-44 days post-insemination. Lack of heart beats, identification of membrane detachment, disorganization or echoic floating structures including embryo remnants were used as indicative of LEL (case). Cows with positive pregnancy diagnosis on the same date of each case were considered as control and the ratio of case-control was 1. For each case animal, the conceptus was sampled (day 0) with an insemination pistol attached to a 10 mL syringe and transported in an Eppendorf tube refrigerated at 4°C to the laboratory. Cows were bled on days 0 and 30 for serological studies. Blood samples were refrigerated at 4°C and transported to the laboratory within 24 h, centrifuged and sera were stored at -20°C until analysis. Sera were tested by indirect fluorescent antibody test (IFAT) for the detection of antibodies against N. caninum using a cut-off titer of 1:200 and processed to final titer. The DNA from conceptus from seropositive cows, was extracted using a commercial kit according to recommendations of manufacturer. The DNA samples were analyzed by PCR with the specific primer pair Np 6+/Np21+ for N. caninum. Chi squared test was used to detect differences between group and P<0.05 was considered as significant.

Results: The proportion of seropositive cows to N. caninum was similar between Case and Control groups (21% [10/46] vs. 15% [7/46]; Chi2=0.574, DF=1; P=0.448). The proportion of cows showing seroconversion was 2.1% (1/46) for both groups (Chi2=1.376, DF=1; P=0.241). Finally, PCR analysis resulted negative for N. caninum DNA in all the conceptus from Case cows (n=12).

Conclusion: We conclude that N. caninum would not be associated with LEL in grazing dairy cows from Argentina.