Internal parasite levels and response to anthelmintic treatment by beef cows and calves

Effects of extended-release eprinomectin on productivity measures in cow-calf systems and subsequent feedlot performance and carcass characteristics of calves

The objective of this study was to estimate the impact of a single injection of extended-release eprinomectin on economically relevant production variables in beef cows and calves as well as subsequent feedlot health, performance, and carcass traits of calves compared with a traditional, short duration anthelmintic. Animals from 13 cooperator herds across seven states were stratified within herd and assigned to one of two treatments; injectable doramectin (DOR; Dectomax; n = 828) or injectable eprinomection (EPR; Longrange; n = 832). Fecal samples were randomly collected from a subset of cows at both treatment and the end of grazing to evaluate fecal egg count (FEC). Continuous and categorical data were analyzed using the MIXED and GLIMMIX procedures of SAS, respectively. Cow treatment body weight (BW) and final BW were not different (P ≥ 0.40) between treatments. There were no differences (P ≥ 0.12) between treatments in cow ADG, change in BW, or body condition scores during the grazing season. While FEC at treatment did not differ (P = 0.18), cows treated with EPR had lower final FEC at the end of the grazing season (P = 0.02) and a greater reduction of FEC over the grazing season (P = 0.01). Calf treatment BW, weaning BW, and ADG did not differ between treatments (P ≥ 0.34). Incidence of pinkeye tended to be less (P = 0.06) for cows treated with EPR but was not different for calves (P = 0.43). Conception to AI, overall pregnancy rates, and calving interval were not different between treatments (P ≥ 0.45). A subset of calves from each herd was sent to Tri-County Steer Carcass Futurity (TCSCF) feedlot for the finishing phase. Calf BW did not differ at initiation of feeding (P = 0.20). While EPR calves tended to be heavier at reimplantation (P = 0.07), final BW and overall ADG were not different between treatments (P ≥ 0.13). Health records indicated lower morbidity for EPR calves (P = 0.05). Carcass performance including HCW, dressing percent, backfat, KPH, REA, YG, were not different between treatment groups (P ≥ 0.12). However, EPR calves had a greater marbling score, greater average quality grade (P < 0.01), and higher proportion of calves that graded average choice or greater (P = 0.03). Results of this study indicate no difference in cow or preweaning calf performance, however, carcass quality in the feedlot phase was improved. Thus, economic analysis indicates opportunities for return on investment if animals treated with EPR have improved health status and/or carcass quality during the feeding phase.

Efeitos da everminação de matrizes e de bezerros lactentes em sistema de produção de bovinos de corte na região de Cerrado

Estudou-se o efeito da everminação de vacas no pré-parto e de bezerros antes do desmame, no número de ovos de nematódeos nas fezes (OPG) e nos parâmetros produtivos em dois rebanhos de gado de corte na região do Brasil Central. Quatro lotes de vacas prenhes receberam os seguintes tratamentos: T1- vacas e bezerros controle, T2- somente bezerros tratados, T3- somente vacas tratadas antes do parto com ivermectina e T4- vacas e bezerros tratados. Os bezerros dos lotes T2 e T4 foram distribuídos nos seguintes grupos: A- tratados aos 3 a 5 meses de idade com ivermectina de ação prolongada, B- tratados com ivermectina e C- controle. Nas vacas a everminação não diminuiu o OPG durante a lactação, como também não teve efeito significativo na taxa de concepção, no ganho de peso e no peso dos bezerros aos 3 a 5 meses de idade. Os bezerros do Grupo A ganharam até o desmame, 84 a 108 dias após o tratamento, em média 4,2kg (P= 0,0003) e 7,1kg (P<0,0001) mais que aqueles dos Grupos B e C, respectivamente. A diferença média, no ganho de peso, de 2,9kg entre os bezerros dos Grupos B e C não foi significativa. Antes do tratamento não houve diferença significativa (P= 0,8665), mas ao desmame, o OPG médio dos bezerros do Grupo A era menor que os do Grupo B (P= 0,0004) e do Grupo C (P< 0,0001). Não houve diferença no OPG entre os bezerros dos Grupos B e C.