Effects of the use of a morantel sustained release bolus in first and second year grazing cattle

In an experiment carried out in 1981 and 1982, the effect of the use of a morantel sustained release bolus (Paratect bolus) on the weight gain and a number of parasitological parameters of cattle was studied. In the first year 42 calves were divided into 3 equal groups, one group was kept outside and treated with a bolus (B), the second group was kept outside and was not treated (C), while the third group remained indoors (I). Groups B and C were grazed separately on contaminated pasture. During the first months Group B had a negligible egg output. The egg output in the controls was much higher and in mid-August they had to be treated for parasitic gastroenteritis. At the end of the grazing season the advantage in weight gain of Group B was 20 kg compared with the controls. During the housing period the growth in the 3 groups was not significantly different. At the start of the second grazing season half the animals of Groups B, C and I received a bolus (Groups BB, CB and IB). The other half remained untreated (BC, CC and IC). The animals treated with a bolus in 1982 gained significantly more weight (64 g/day) than untreated animals. Heifers turned out for the first time (IB and IC) showed much less weight gain than heifers in their second grazing season. The heifers which had previously grazed in 1981 had a very low egg output compared with Groups IB and IC, although the level of egg output of the latter was also not very high (max, almost 40 (eggs per gram (EPG)). In faecal cultures of heifers of Group BC, CB and CC, no Cooperia oncophora-larvae were seen from May onwards, indicating a strong immunity against this species. In Group BB very low numbers of C. oncophora-larvae were observed. In Groups IB and IC, C. oncophora was present during the whole season. At the end of the first season the level of herbage infestation on the control pastures was much higher. In 1982 only slight differences in level of infestation between the pastures were observed. At the start of the season in 1982 serum pepsinogen levels were much higher in the groups which grazed in 1981, compared with the indoor-fed groups. Groups BC and CC had significantly higher levels than Groups BB and CB and all 4 groups always had higher levels than Groups IB and IC.(ABSTRACT TRUNCATED AT 400 WORDS)