Short communication: Effects of fluoxetine on lactation at weaning in sheep.

Selective serotonin reuptake inhibitors have been considered for use in the dairy industry to aid in dry-off procedures because of their ability to delay the onset of lactation. Fluoxetine (a selective serotonin reuptake inhibitor; FLX) is an agent that has been shown to delay the onset of lactogenesis stage II when taken during pregnancy and lactation in women. Two experiments were conducted to determine whether ewes would be an appropriate model to evaluate the effects of FLX on milk production at weaning. In the first experiment, 12 Suffolk cross ewes (body weight = 83.4 ± 12.2 kg; body condition score = 2.1 ± 0.4) in late lactation were assigned to treatments of 0 (control), 40, or 80 mg of FLX. They were given a single subcutaneous injection with the appropriate level of FLX mixed with propylene glycol at 0700 h on approximately d 78 of lactation (the day lambs were removed). In the second experiment, 18 Suffolk cross ewes (body condition score = 1.8 ± 0.3) from a previous lactation study were selected in late lactation. On approximately d 66 following parturition, weaning was initiated and ewes received a single oral bolus treatment (0, 80, or 160 mg of FLX). Treatment was administered using gelatin capsules containing the appropriate dose of FLX. For both experiments, milk production was estimated: in experiment 1 on d 0 (before treatment), 1, 2, and 3 (after treatment) at 0800 and 1100 h, and in experiment 2 on d 0, 1, and 2 following treatment at 0800 or 1100 h. Milk production was measured over a 3-h period. We observed no treatment differences or day effects on milk production in either experiment. In experiments 1 and 2, as the dose of FLX increased, milk production decreased linearly. Serum lactose concentrations were depressed in ewes treated with FLX in experiment 1 but similar across treatments in experiment 2. Overall, FLX depressed milk production in ewes; therefore, there is potential to use FLX as a dry-off agent in the dairy industry.