The effect of eprinomectin treatment at calving on reproduction parameters in adult dairy cows in Canada.
A clinical trial was carried out in two provinces of Canada to investigate the effect of treatment with eprinomectin at calving on production parameters in adult dairy cattle in 1999-2000. One of the objectives of this study was to evaluate the impact of treatment on reproductive performance as measured by: calving-to-conception interval, calving-to-first service interval and number of services per conception. The ability of an indirect ELISA using a crude adult Ostertagia ostertagi antigen to predict response to treatment also was evaluated. All lactating cows in 20 dairy herds were allocated randomly to receive either eprinomectin pour-on or placebo at calving. Information on reproductive parameters was obtained from computerised cow records. Survival models were used to evaluate the effect of treatment on the two intervals and a Poisson model was used to evaluate the number of services to conception. A total of 549 cows were included in these analyses. A marginally significant treatment effect on calving-to-conception interval was observed (hazard ratio=1.24, P=0.06) but not on calving-to-first service interval. A significant reduction in the number of breedings to conception for treated animals also was observed with a longer effect in cows with short interval to first service. Milk samples from a subset of 109 late-lactation cows were tested for antibodies against O. ostertagi. The ELISA optical-density ratio (ODR) values obtained between 120 days before calving and drying off were categorised as high ODR (>or=0.5) and low ODR (<0.5). Among untreated animals, the hazard of conception was lower (hazard ratio=0.38, 95% CI=[0.19,0.75]) for high-ODR cows compared to low ODR cows suggesting that higher parasite burdens had an adverse effect on reproductive performance. Treated high-ODR cows had a hazard of conception equivalent to the hazard for all cows in the low-ODR group (indicating that treatment prevented the negative effect associated with these higher parasite burdens).
Sanchez
J
J
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, PEI, C1A 4P3, Charlottetown, Canada. jsanchez@upei.ca
Nødtvedt
A
A
Dohoo
I
I
DesCôteaux
L
L
D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage / Q000494:pharmacology*; D000947:Antigens, Helminth / Q000032:analysis; D002417:Cattle / Q000254:growth & development*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D007559:Ivermectin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*; D010028:Ostertagia / Q000276:immunology / Q000302:isolation & purification / Q000472:pathogenicity*; D010029:Ostertagiasis / Q000150:complications / Q000517:prevention & control*; D011247:Pregnancy; D012098:Reproduction; D013534:Survival
D000871:Anthelmintics; D000947:Antigens, Helminth; D007559:Ivermectin; C101434:eprinomectin