CONICET | Buscador de Institutos y Recursos Humanos

Gastrointestinal parasitism is a major constraint to animal health, productivity, and profitability in grazing livestock production systems. Nowadays, it is critical to identify parameters to focus anthelmintic treatment, avoiding massive drug use which may certainly generate drug resistance. The study was performed in the dairy farm at the Experimental School of Inchausti, 25 de Mayo, Province of Buenos Aires, Argentina (35°36 S, 60°32 W). Cows were individually sampled for rectal feces, coccigeal vein blood and milk during their first month after calving. Nematode eggs (EPG) were counted in feces by the Mc Master method adapted by INTA. Pepsinogen (P) was measured in serum by the colorimetric method of Ross et al. and expressed as Tyrosine mU/ml. Anti Ostertagia antibodies concentration was evaluated in milk by the Svanova ELISA kit and Optical density ratio (ODR) calculated according to manufacturer instructions. Individual daily milk production was recorded by means of the Alpro-Milking computarized system and lactation curves were performed for each cow. Average milk production of the herd at 305 days was 7173 + 18 liters (N=127). For each parameter indicating parasite infection, cows were separated in two groups (low and high infection) and total milk production was compared between both groups by Student t-test (EPG = 0 vs EPG >0, P <= 1000 vs P > 1000 and ODR <= 0.5 vs ODR > 0.5). Milk production in liters at 305 days was (mean + SEM) 7303 + 21 vs. 6867 + 31, 7275 + 180 vs. 7127 + 99 and 7078 + 75 vs. 6825 + 37, for each previously mentioned parameter, respectively. Significant differences in milk production were only evidenced when cows were separated by their EPG values in high and low infection groups (p< 0.05). We conclude that EPG evaluation post-calving is a useful tool for determining gastrointestinal parasite infection which depresses milk production and may help to focus anthelminthic treatment in adult producing cows