Gastrointestinal nematodes of young cattle. Behavior in Cuban silvopastoral systems


Mildrey Soca Pérez
Estación Experimental de Pastos y Forrajes Indio Hatuey Central España Republicana 44280, Matanzas, Cuba


In order to determine the epizootiological behavior of the gastrointestinal nematodes of young cattle in silvopastoral systems, three trials were developed under experimental and commercial conditions, related to the parasitological dynamics in the excreta, the seasonal behavior of nematode infestations in the animals and the validation studies. Two systems were evaluated: A) Silvopastoral system (SS) and B) System without trees (SWT), in the dry season (DS) and rainy season (RS) and young cattle of the genotype 5/8 Holstein x 3/8 Zebu were used, with an age between 5 and 7 months and an average weight of 60-90 kg. When evaluating the parasitological dynamics of the droppings (Experiment 1), the SS showed a fast decomposition rate (P < 0,001), higher than 95 % after 10 and 4 days of deposition for the DS and RS, respectively; in the SWT the decomposition was slower in the DS with 42 %, for the same deposition time. This process was more accelerated in the rainy season, and was related to the fragmentation and dispersal of the excreta because of rainfall. In the SS a significant increase was found (P < 0,05) of the number of individuals per square meter (1 116 vs 2 547) and of individuals per dropping (14,51 vs 32,94) (P < 0,01), in the DS and RS, respectively. The fecal egg count (FEC) showed a decrease of 98 % at 168 hours in the DS, and of 100 % at 96 hours after being deposited in the RS. Significant correlations were found (P < 0,001) between the decrease of dropping weight and the FEC, with a correlation coefficient r = 0,92 in the dry season and r =0,95 in the rainy season. This behavior was related to the presence of coprophagous coleopterans in the droppings, which were significantly higher (P < 0,01) in the SS.
In Experiment 2, the presence of the genera Oesophagostomum and Haemonchus was found; the latter was the one with the highest incidence per year and per season, in both systems. The FEC showed significant differences (P < 0,01) since the second year of evaluation in favor of the SS, with values below 800 epg. A similar behavior was shown by the average of the annual FEC (520 vs 1 412) and per seasons: DS (471 vs 1 183) and RS (596 vs 1 814), which was significantly lower (P < 0,001) in the SS. Under commercial conditions, the FEC showed a sustained decrease in time until reaching non-compromising levels for the health of the animals. The live weight upon their incorporation to the SS did not have influence on the parasite rate and the best results were achieved with higher weights than 80 kg. The deworming of the animals before their incorporation to the SS allowed them to maintain, in time, low levels of parasite infestation. The FEC did not show significant differences between the animals of different sexes, although in the males a trend was observed to show numerically higher infestation values. The stability and the better performance of these parasite infestations in the SS were related, with the decomposition process of the dropping, with the dry matter availability, the pasture height and the chemical composition of the herbaceous and tree strata. The results reached in all the experiments confirm the potential of these systems to contribute, significantly, to the decrease of nematode infestations in young cattle under Cuban conditions. The scientific novelty of this thesis is that for the first time studies are conducted in Cuba about the seasonal behavior of gastrointestinal nematodes in young cattle in SS, the first results are offered about the decomposition of calf droppings, in SS and in monocrop grazing; the role of the coprophagous fauna in the decrease of parasitism of the droppings in grazing systems is approached; the evolution of the FEC is characterized, taking into consideration the structure of the droppings in grazing systems and the potentialities of SS for calf rearing are proven.