Scanning electron microscopy (SEM) was used to study the endometrium of nine 1-year-old thoroughbred mares after twice intrauterine infusions of gentamicin, on 2 consecutive days. Five mares were infused on 2 consecutive days with 40 ml gentamicin (50 mg/ml) mixed with 80 ml of normal saline. Four mares served as controls and were infused with 120 ml of saline on 2 consecutive days. Endometrial biopsies were obtained from all mares 3 days after the second intrauterine infusion. Each biopsy was processed for SEM by standard methods. The endometrial epithelium of the gentamicin-infused mares had more cellular perforations than the saline-infused mares. The gentamicin-infused mares had less and shorter microvilli. The ciliated cells were fewer and some ciliated cells had disrupted and some had drooping cilia. The endometrial epithelium of the gentamicin-infused mares had a considerable number of endometrial cells that lost their luminal surfaces and some that lost their microvilli, compared to the saline-infused mares. We suggest that the information gathered in this pilot study should be used as basis for further investigation, on a larger scale basis, of the effects of repeated intrauterine infusion of gentamicin on the endometrial mucosa of mares.

Voluntary food intake, milk production and blood characteristics were measured in mares between the 3rd month before foaling and the first 5 weeks of lactation. The effect of breed during pregnancy was determined using 15 light mares and eight heavy mares (522 and 763 kg live weight (LW) after foaling respectively). The effect of parity was studied on light mares (seven were primiparous and eight were multiparous). In lactation, only four primiparous and four multiparous light mares were retained. Diet consisted of 900 g hay and 100 g concentrates per kg and was offered ad libitum. Voluntary food intake in pregnancy was higher for heavy mares than for light mares: 15·2 v. 10·3 kg dry matter (DM) daily. This difference was explained by differences in LW, since DM intake was the same when expressed as a fraction of LW or metabolic weight (M). Energy and nitrogen supply exceeded requirements, in the same way for light and heavy mares. No significant variations in blood measurements were observed between light and heavy mares, except for glucose. Primiparous mares ate less DM than multiparous mares in pregnancy: 9·7 v. 10·8 kg DM (P > 0·05), significantly so relative to LW and M. DM intake per kg LW or M depended on the parity. This difference had no effect on blood measurements, except for acetate. During lactation, no other differences in voluntary food intake were observed with regard to parity, whatever the week of lactation. Milk yield was higher for multiparous mares than for primiparous mares (16·6 v. 14·6 kg daily). Gross energy of milk varied according to a similar pattern, principally because of variations in fat concentration (20·2 v. 16·5 g/kg for multiparous and primiparous mares respectively). Energy balance was significantly more positive for multiparous than for primiparous mares.