In 2002, Grisi et al. made an attempt to assess the economic impact of cattle parasitism in Brazil. The resulting study was regarded as an important source of data on the economic drag that endo and ectoparasites inflict on cattle, especially from the producer's point of view. More than 10 years later, a lot has changed in the Brazilian livestock scenario: new data regarding production losses due to parasites have become available from many regions of the country. Hence, there was a need for an update.

Occurrences of internal and external parasites in cattle throughout Brazil are favored by the predominance of tropical and subtropical climates. The national cattle herd is estimated to comprise 212,797,824 heads, distributed over 8 million square kilometers of land (IBGE, 2011).

The economic impact of external parasites on cattle is mostly associated with infestations by the cattle tick, Rhipicephalus(Boophilus) microplus, horn fly (Haematobia irritans), cattle grub (Dermatobia hominis) and New World screwworm (Cochliomyia hominivorax). Furthermore, the importance of the stable fly (Stomoxys calcitrans) has increased over the last few years because of outbreaks associated with postharvest residues of the sugarcane industry (^{BARROS et al., 2010a}). Other ectoparasites, such as the cattle mange and sucking and chewing lice, are seasonal and limited to the southern regions.

^{Drummond et al. (1981)}estimated the annual losses due to cattle parasites to be $2,260 million in the United States, not including the costs of parasite control. This figure represented 10% of the value of production and sales at the time. The annual loss estimates for specific pests ranged from $29.7 million for scabies and mange mites to $730.3 million for horn flies. The cattle population in the USA in 1981 was estimated to be 124.7 million (NASS; USDA, 2011).

^{Grisi et al. (2002)} estimated that the total economic losses due to ectoparasites in cattle in Brazil were $2,650 million. At that time, economic losses relating to the most important ectoparasite, the cattle tick, were based in a previous estimate by Horn (1983) of $968 million for a national cattle herd of 76 million head.

The potential economic losses due to cattle parasitism in Brazil caused by major ectoparasite species and gastrointestinal nematodes are evaluated here. Estimates of the potential economic losses of each parasite species or group are based on numbers of animals at risk and on the available data on losses in milk production and weight gain of beef cattle. Most of the data are from local studies; when such information is unavailable, estimates are based on selected studies conducted elsewhere. Because information regarding production losses was obtained from control animals (animals kept untreated in the respective studies), the resulting estimates of economic losses represent potential losses among untreated cattle. Thus, the estimates presented do not necessarily represent the actual impact of cattle parasitism in Brazil but the potential losses expected in the absence of parasite control measures.

The impact of gastrointestinal nematodes on cattle production has been extensively studied worldwide. ^{Lima and Grisi (1984)} assessed the milk production of cows medicated with albendazole at parturition in the state of Rio de Janeiro in comparison with controls, and reported an increase of 51.90 kg of milk per cow in the medicated group during the 90-day study period, which corresponded to 0.58 kg of milk/cow/day. ^{Ploeger et al. (1989)} conducted a similar study in Holland and reported an increase of 0.44 kg of milk/cow/day. ^{Charlier et al. (2009)} summarized the data prior to 1997 from studies on the impact of subclinical gastrointestinal parasitism in dairy cattle, and showed that medication produced an increase of 0.4 to 0.8 kg of milk/cow/day. Considering an average loss of 0.6 kg of milk per cow per day without medication, the potential losses of the dairy cattle population at risk due to gastrointestinal worms in Brazil would be $1,870.48 million (Table 1).

Based on 6 years of field trials with weaned Nelore cattle on improved pastures in central-western Brazil, ^{Bianchin et al. (1995)} showed that there was a superior average weight gain of 41 kg when the animals were dewormed following a strategic program. Likewise, studies conducted by Pinheiro (1983) showed that there was a difference of 67 kg in weight gain per animal between treated and untreated groups in the southern region. Analysis on data relating to beef cattle yearlings and heifers up to 2 years old showed that the potential losses due to helminth parasitism amounted to $5,237.49 million. Because of control problems commonly observed in the field, the potentially high losses due to gastrointestinal nematodes in dairy and beef cattle, estimated as $7,107.97 million (Table 1), strongly suggest that this parasitism represents the most important economic problem due to parasites in the country.

The damage to milk production caused by cattle ticks was recently evaluated by ^{Rodrigues and Leite (2013)} in the state of Minas Gerais, where 24.2% of the country's dairy cows are concentrated. These authors estimated that ticks were responsible for a reduction of 90.24 L in milk production per cow per lactation, which, when extrapolated to the national dairy herd, amounted to about $922.36 million of losses to the national dairy herd. Estimates of the losses inflicted by cattle tick on beef cattle were based on ^{Jonsson (2006)}, who reported daily losses of 1.18 and 1.37 grams per tick per animal for Bos indicus x Bos taurus cattle and B. taurus, respectively. Average tick infestations were obtained from ^{Smith et al. (2000)} for B. taurus (94 ticks/animal) and ^{Gomes et al. (1989)} for B. indicus (3.3 ticks/animal) and crossbreeds (32 ticks/animal). Considering the whole Brazilian beef cattle herd (about 11% B. taurus and 89% B. indicus and crossbreeds), the potential economic losses caused by this tick on beef cattle were estimated to be $2,313.99 million. Therefore, the total economic loss attributable to R.(B) microplus in the Brazilian cattle herd may approach $3,236.35 million (Table 2).

Losses due to horn fly infestation were based on the studies of ^{Bianchin and Alves (2002)} and ^{Bianchin et al. (2004)}, which estimated average yearly weight losses of 3.25 kg per cow, 2.00 kg per calf and 12.19 kg per steer (value also used for heifers). Considering populations at risk, as well as current market values, the total losses due to horn fly parasitism in Brazil approach $2,558.32 million (Table 3). Although infestations by the horn fly and the closely related buffalo fly (H. irritans exigua) may reduce milk production (^{JONSSON; MAYER, 1999}), the relatively low infestations usually observed on dairy cattle, probably due to frequent cattle tick treatments, suggest that the impact of horn flies may be not so evident in Brazil. No estimate of horn fly losses on dairy cattle or beef cattle pregnancy rates is provided here, since these subjects need further investigation.

The data on damage caused by D. hominis larvae to cattle productivity were based on ^{Magalhães and Lesskiu (1982)}, who found a yearly reduction in weight gain of 40.6 g per larva. The estimates of economic losses due to the cattle grub focused on regions where this parasite is abundant and important. Thus, average infestations on B. taurus (74 larvae/animal/year) and B. indicus (18.2 larvae/animal/year) were estimated for the central-western and southern regions, as well as for the state of Paraná, based on several studies (^{MAGALHÃES; LESSKIU, 1982}; ^{SARTOR, 1986}; ^{GOMES et al., 1988}, ¹⁹⁹⁶; ^{CARNEIRO et al., 1990}; ^{OLIVEIRA, 1991}; ^{PINTO et al., 2002}; ^{FERNANDES et al., 2008}; ^{SOUZA et al., 2010}). Considering that 19.12 million B. taurus and 90.96 million B. indicus are at risk, the potential losses in weight gain due to this parasite amount to $201.93 million yearly.

The rate of damage to cattle hides caused by D. hominislarvae averaged 25.17% at slaughterhouses in the regions studied (^{BRITO; MOYA-BORJA, 2000}; ^{MARQUES et al., 2000}; ^{SANAVRIA et al., 2002}), which represented annual losses of about $181.55 million. Cattle hide damage caused by both cattle grubs and cattle ticks reached a rate of 40%, as officially reported from a previous survey (BRASIL, 1983). Considering losses in relation to both weight gain and hide damage, the potential losses due to D. hominis larval infestation total $383.48 million (Tables 4 and 5).

Occurrences of navel myiasis due to screwworm have been reported in 40.7% of calves in central-western Brazil (^{BIANCHIN et al., 1992}), which is the main region for raising beef cattle in this country. Although endectocide products have been widely used to prevent and treat navel myiasis in newborn calves throughout Brazil, considerable losses persist. Barros et al. (2010b) reported a 5.5% control failure rate for endectocide treatments against navel myiasis in calves, which was similar to the mortality rate (5.32%) observed among 432 calves monitored until weaning (^{BIANCHIN et al., 1992}). Considering a natural occurrence of 40.7% for screwworm attacks among calves and that 5.5% of treated animals may still develop myiasis, the losses due to potential calf mortality were estimated to be $310.55 million (Table 6). Considering the population at risk to be just a small proportion of the calf population (i.e. only the animals presenting control failure and at risk of death), rather than the entire population of calves at potential risk of infestation, the estimated economic losses due to this parasite are probably closer to reality, but comparatively lower than those estimated for other parasite species. No estimate of the losses due to screwworm attacks among adult animals was possible, because of the lack of specific information, but this parasite and its economic implications certainly play an important role in several regions of this country.

The potential losses due to stable flies (S. calcitrans) were based on Kunz et al. (1991), who reported estimated losses of 100 g per steer per day in feedlots (50% of the cattle were exposed to stable flies) and a 27 kg decrease in milk production per cow per year (stable flies were present for six months), in the USA. Considering that there are 4.08 million feedlot cattle in Brazil (ABIEC, 2013), the losses due to S. calcitrans were estimated as $59.49 million (Table 7). Regarding milk production, the losses inflicted on dairy cattle were estimated as $275.97 million. The total loss of $335.46 million attributed to stable flies is probably an underestimate, since the impact of this pest on pastured cattle and the size of the affected population, particularly during severe outbreaks, is unknown and was not included here. In addition to the fact that losses during outbreaks are much higher than in regular infestations, it should be considered that the frequency and severity of these outbreaks in Brazil are increasing dramatically due to the rapid expansion of ethanol production from sugarcane. The present estimate of potential losses due to stable flies is much lower than the economic impact of $2,211 million per year recently estimated for this pest among dairy and beef cattle in the USA (^{TAYLOR et al., 2012}). Further investigations are needed regarding the current impact of stable flies on cattle production in Brazil.

Thus, the following economic losses, in millions of dollars, were estimated regarding the impact of these parasite species or groups for the respective cattle populations that were considered to be at risk: gastrointestinal nematodes ($7,107.97), cattle ticks ($3,236.35), horn flies ($2,558.32), cattle grubs ($383.48), screwworms ($336.62) and stable flies ($335.46).

The annual potential economic losses due to the five major ectoparasites and gastrointestinal worms of cattle in Brazil reach the impressive amount of $13.9 billion (Table 8). This reflects the favorable environmental conditions for both livestock and their parasites in this country. The situation is aggravated by parasite control bottlenecks. When distributed across the national cattle herd (more than 212 million head), a yearly loss of $65.49 per head was found, which might seem to be more tolerable. However, considering an average age at slaughter of 36 to 42 months, this yearly impact actually represents 32% of the beef cattle sale price (CEPEA, 2013a, b, c), thus making the potential damage due to cattle parasitism unacceptable for both producers and the cattle industry.

Regardless of the limitations of some of the baseline studies used to develop these estimates, particularly when extrapolated from local situations to a national scale, the general picture obtained from the present effort demonstrates the magnitude and importance of cattle parasitism in Brazil and the unfeasibility of a profitable livestock industry without proper parasite control.

Traditionally, chemicals have been used to manage parasites, with an impact on the wellbeing and health of domestic animals, including food-producing livestock (^{ECOBICHON, 2001}; OLIVEIRA PASIANI et al., 2012). However, indiscriminate use of chemical pesticides for veterinary use has driven parasite populations to become resistant to many of them (^{ANDREOTTI et al., 2011}; ^{KAPLAN; VIDYASHANKAR, 2012}; CASTRO JANER et al., 2012). Further studies assessing the contribution of pesticide resistance to the economic harm resulting from parasitic diseases in cattle are warranted.

Ultimately, establishment of a national program of parasite control and resistance management, as well as a solid extension program, will not only reduce the real impact of parasitism on the Brazilian cattle industry – taking it far from the potential damage currently estimated – but also enhance public and animal health.