Domestic Quarter Horse (Equus caballus) Milk Macronutrient Composition Analyses Within Micro Quantities from Two Different Geographical Locations.

Microquantity laboratory procedures (<5 mL) are often used to analyze milk from non-bovid or less common species due to limited available samples and small sample sizes, unlike the large quantities of milk needed for macroquantity (~20 mL) assays standard in the commercial dairy industry. To better understand microquantity milk laboratory analyses, quarter horse (Equus caballus) milk from North Carolina State University (females = 4, n = 43) and California Polytechnic State University (females = 4, n = 42) equine centers was compared to investigate differences in macronutrient composition from 4 to 130 days after parturition. All mares were healthy, but consumed different diets. Major milk macronutrients were measured at the Smithsonian National Zoo and Conservation Biology Institute using a microquantity analysis of ash, crude protein (CP), dry matter (DM), crude fat, sugar, and gross energy. Of the six measured nutrients, only CP and crude fat differed (p < 0.05) by location, while sugar and crude fat had differences among individual mares. Californian mares had greater fat concentration means on a dry matter basis (DMB) than the North Carolinian mares (ANCOVA, p = 0.003). North Carolinian mares had greater CP concentration means than Californian mares. These findings indicate that dietary differences and/or environmental factors may play a role in CP and crude fat milk macronutrient composition within horse breeds. However, despite the differences noted, the microquantity analyses for nutritional means for all eight mares were within macroquantity horses ranges available in the previous literature. The results indicate that micro versus macroassays are comparable and supports clinical and scientific research on milk from species where large sample quantities are difficult to obtain.