ENDOCRINE AND METABOLIC RESPONSES TO TRANSPORTATION IN PERIPARTURIENT

Periparturient equidae are particularly susceptible to hyperlipaemia, a severe metabolic disorder that can be induced and aggrevated by stre ssful situations. To define maternal endocrine and metabolic adaptatio ns to the peripartum period, plasma concentrations of progesterone, oe stradiol, 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM), trigly ceride, cholesterol, glucose, total protein, urea, cortisol and insuli n were examined in two donkey mares throughout late gestation (-50 day s), parturition (Day 0) and early lactation (+100 days), and in one no n-pregnant mare over six oestrous cycles. Maternal progesterone and oe stradiol concentrations increased towards term, to maxima of 50-60 nmo l l(-1) and 130-170 pmol l(-1), respectively, and decreased rapidly fr om 2 days prepartum to <5 nmol l(-1) and <15 pmol l(-1) at parturition . Plasma PGFM concentrations of 8-11 nmol l(-1) over 1 week prepartum decreased to <1 nmol l(-1) 1 day postpartum. Maternal triglyceride con centrations increased from 1-2 mmol l(-1) over late gestation to a max imum of 2-4 mmol l(-1) at parturition. Thereafter, values rapidly decr eased to <0.5 mmol l(-1) by 3 days postpartum. Plasma cholesterol and total protein profiles also followed this pattern; no consistent chang es were evident in glucose, urea, cortisol or insulin concentrations. To assess endocrine and metabolic responses to a stressor in animals u nder gestational or lactational energy demands, plasma cortisol, trigl yceride, cholesterol, glucose and insulin concentrations were examined in the same two donkey mares transported for approximately 4 h at 3-1 0 weeks prepartum and 2-9 weeks postpartum. These responses were compa red with those observed in non-pregnant donkeys. Transportation increa sed cortisol concentrations in pregnant (maximally by 215 and 130%), l actating (32 and 85%) and non-pregnant animals (145+/-9%). Plasma gluc ose concentrations remained stable in all but one lactating donkey; th e hyperglycemic effect may have been an indirect indicator of a reduce d tissue sensitivity to insulin. Stressor-induced suppression of circu lating insulin was apparent in postpartum (-57 and -51%) and non-pregn ant animals (-46+/-4%). Triglyceride and cholesterol concentrations in all donkeys were unchanged by transportation. The observed shifts in lipid metabolism, possibly facilitated by gestational changes in conce ntrations of progesterone and oestradiol, are likely to make the perip artum mare vulnerable to the development of equine hyperlipaemia. Howe ver, an additional environmental stressor (4 h transportation), which stimulated an adrenocortical response in periparturient donkeys, was u nable to induce any consistent alteration in metabolic function or evi dence of potential dysfunction.