Epidermal growth factor alters milk composition and fluid balance of lactating ewes

Lactating ewes were treated with murine epidermal growth factor (EGF) and its effects on concomitant milk production and composition were observed. Six ewes were infused via the jugular vein with 200 ml saline/day over 4 days (days 9-12 of lactation) followed by EGF at a dose rate of 0.5 mg/day in 200 ml saline over 4 days (days 13-16). All ewes then received a further infusion of 200 ml saline/day over 4 days (days 17-20). During the experiment a maintenance (lactation) diet was offered and ewes were machine-milked twice daily. An EGF-immunoreactive material was detected in mammary secretions and urine throughout the experiment, but only in plasma (1-9 micrograms/l) during the period of EGF infusion. The amount of EGF appearing in milk and urine increased from 37 micrograms and 10 micrograms respectively (day 1 of EGF infusion) to 56 micrograms and 17 micrograms respectively (day 4). EGF treatment resulted in lower milk yield and reduced concentration of lactose and protein; milk fat concentration fell after EGF infusion had ceased. Water intake increased markedly during EGF infusion and was 60% (4 kg) greater on day 4 than that measured during the first saline infusion. Urine volume also increased and was 164% (3.6 kg) greater by day 4 of EGF infusion compared with that recorded in the first saline infusion. Water retention (intake minus output in milk, urine and faeces) was significantly higher on the day after EGF infusion ceased than that found during the first saline infusion. The possibilities that the increased water intake was primary, or secondary, to a diuretic effect of EGF are discussed.