title: Effect of vehicle and route of administration of letrozole on ovarian function in a bovine model.
abstract: The objective of this study was to determine the effects of vehicle and route of administration of letrozole on ovarian function in sexually mature beef heifers. On Day 3 (Day 0=ovulation), heifers were assigned randomly to four treatment groups and given 1mgkg(-1) letrozole intravenously (iv, n=10) or intramuscularly (im, n=10) or given a placebo iv (control iv, n=5) or im (control im, n=5). The interwave interval was longer in heifers treated with letrozole im than in im and iv controls (11.7±0.30 vs 9.5±0.50 and 10±0.43, respectively; P<0.05). Corpus luteum diameter profiles and plasma progesterone concentrations were greater (P<0.03 and P<0.05, respectively) in heifers treated with letrozole im compared with control im. Plasma oestradiol concentrations were lower in both letrozole-treated groups compared with controls (P≤0.03). Plasma LH concentrations tended to be elevated at the time of wave emergence in heifers treated with letrozole im compared with other groups (group-by-day interaction, P=0.06) and plasma FSH concentrations tended to be greater (P<0.09) in heifers treated with letrozole by either route compared with a single control group. We conclude that intramuscular administration of letrozole in oil is a feasible route and vehicle for the development of a letrozole-based treatment protocol for herd synchronisation in cattle.
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Yapura
authors.affiliation: Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
authors.forename: R J
authors.initials: RJ
authors.lastname: Mapletoft
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Sciences, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W8, Canada.
authors.forename: R A
authors.initials: RA
authors.lastname: Pierson
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
authors.forename: G P
authors.initials: GP
authors.lastname: Adams
mesh_terms: D000818:Animals; D019905:Benzyl Alcohol / Q000737:chemistry; D015415:Biomarkers / Q000097:blood; D002417:Cattle; D002626:Chemistry, Pharmaceutical; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism; D004958:Estradiol / Q000097:blood; D004973:Estrus Synchronization / Q000187:drug effects*; D005240:Feasibility Studies; D005260:Female; D005300:Fertility Agents, Female / Q000008:administration & dosage* / Q000737:chemistry; D007273:Injections, Intramuscular; D007275:Injections, Intravenous; D000077289:Letrozole; D007986:Luteinizing Hormone / Q000097:blood; D023421:Models, Animal; D009570:Nitriles / Q000008:administration & dosage* / Q000737:chemistry; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000378:metabolism; D014677:Pharmaceutical Vehicles / Q000737:chemistry; D011374:Progesterone / Q000097:blood; D012715:Sesame Oil / Q000737:chemistry; D013997:Time Factors; D014230:Triazoles / Q000008:administration & dosage* / Q000737:chemistry; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; D005300:Fertility Agents, Female; D009570:Nitriles; D014677:Pharmaceutical Vehicles; D014230:Triazoles; D011374:Progesterone; D004958:Estradiol; D000077289:Letrozole; D012715:Sesame Oil; D007986:Luteinizing Hormone; D019905:Benzyl Alcohol