Influence of maternal plane of nutrition on mares and their foals: determination of mare performance and voluntary dry matter intake during late pregnancy using a dual-marker system.

Thirty pregnant mares (538 to 695 kg BW; 4 to 19 yr of age) were used to evaluate the effects of plane of nutrition on DMI of hay and mare performance (BW, BCS, and rump fat) during the last third of pregnancy. Mares were divided into 4 blocks by their expected foaling date and randomly assigned within block to either a hay or concentrate plus hay diet (concentrate fed at 0.75% BW, as-fed basis) with 15 mares per treatment. Treatments began 110 d before expected foaling date (230 d of gestation) and terminated at parturition. Mares were housed by block and allowed ad libitum access to coastal Bermuda grass (C. dactylon) hay, and concentrate-supplemented mares were fed twice daily in individual stalls. Performance variables were recorded every 14 d, with the last measurements obtained before foaling being considered a prepartum measurement. To evaluate DMI of hay, a dual-marker system was used at 9, 10, and 11 mo of gestation. Titanium dioxide was dosed at 10 g for 14 d. Fecal grab samples were obtained on the last 4 d twice daily via rectal palpation at 12-h intervals with times advancing 3 h each day to account for diurnal variation and to ultimately represent a 24-h period. Fecal samples were analyzed for TiO2 using a colorimetric procedure. Fecal, concentrate, and hay samples were also analyzed for acid detergent insoluble ash. Treatment tended to influence prepartum BW (P = 0.09) and affected prepartum BCS (P < 0.01) and rump fat (P = 0.01), with hay-fed mares having decreased BW and BCS from d 0 (beginning of feeding trial or d 230 of gestation) until parturition, whereas mares fed concentrate gained BW and BCS (P < 0.01). Mares fed only hay consumed 2.3% BW of forage compared with 1.8% BW for concentrate-fed mares (P < 0.01). Regardless of treatment, month of gestation influenced forage intake (P < 0.06), with mares consuming less during the 10th month of gestation and more in the 11th month (1.9% and 2.2% BW, respectively). These data indicate that the altered plane of nutrition of mares in late gestation influenced mare performance. Furthermore, DMI of hay was influenced by both diet and month of gestation. Continued research investigating manipulation of maternal nutrition and its effects on DMI would be beneficial to completely understand the relationships of these observations.