Effect of Stage of Reproduction and Diet On Bone Density In Lactating Mares - CRF Horse Nutrition Guide
E UK17 - CRF Equine Research Trials
Effect of Stage of Reproduction and Diet On Bone Density In Lactating Mares
| CRF Horse Nutrition Guide |
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| CRF Equine Research Trials |
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During pregnancy and lactation, maternal bone mineral may be used to meet the nutrient demands of the developing fetus and milk production. In other species, a few studies have examined the balance between bone mineralization and bone resorption in pregnant or lactating individuals by measuring biochemical markers of bone turnover. But in equine most studies have involved the skeletal development in growing horses.
Two common markers of bone turnover that can be measured in serum are osteocalcin and carboxyterminal telopeptide of type 1 collagen (ICTP). Increased serum osteocalcin concentration is associated with increased bone mineralization, with the highest concentrations usually reported in young animals. ICTP is released during the breakdown of type-1 collagen and may be a useful indicator of bone resorption.
Three studies were conducted to assess changes in circulating concentrations of osteocalcin, ICTP and bone mineral density in mares with different pregnancy and lactation status; and to determine whether calcium intake affects indicators of bone mineral metabolism during late lactation or after weaning.
In the osteocalcin and ICTP studies all mares received a commercial 14% crude protein concentrate, two times a day. On average, pregnant mares were receiving approximately 30% more concentrate than non-pregnant mares (3 to 4 kilograms per day versus 2 to 3 kilograms per day). In the calcium/bone mineralization study mares were blocked and assigned to either a control treatment (100% of 1989 National Research Council requirements) or high calcium treatment at 150% of the control. The nutrients provided by the forages were also taken into account.
- Blood samples were obtained from each mare for analysis of osteocalcin and ICTP as previously described. Radiographs of the right and left third metacarpal were taken using the radiographic step-wedge method in the calcium study.
- ICTP concentrations did not differ among mares that had varying pregnancy and lactation status. Pregnant mares had lower (P < 0.05) osteocalcin concentrations than non-pregnant mares. Pregnant mares that had nursed a foal had numerically lower osteocalcin concentrations than pregnant mares that had not nursed a foal, but the difference was not significant.
- Data suggest the possibility that bone resorption is most active during late gestation and early lactation, and then bone mineralization increases in late lactation and after weaning. Bone mineralization may be decreased for pregnant mares compared to non-pregnant mares, but returns to normal late in lactation and after weaning.
- No changes in bone mineral density were detected in this experiment. Radiographs from some mares appeared to show a trend for lower bone density during lactation, but opposite observations were made for other mares.
- While these data indicate that the current National Research Council (1989) recommended calcium intake is adequate for lactating mares, the bone mineralization indicators suggest that pregnancy and lactation do put stress on the bone mineralization status of mares. Consequently, this study emphasizes the importance of feeds designed to meet the increased mineral demands of brood mares.
- Levels of calcium and phosphorus in current horse feed formulations used by CRF member feed companies are adequate for pregnant and lactating mares.