75 Sampling technique affects mare milk composition

Abstract

Accurately measuring milk composition is important for many research studies. Different techniques are utilized to collect milk samples; however, little is known of the effect of sampling technique on mare milk composition. The objective was to compare milk composition collected by 3 sampling techniques and evaluate changes in composition within an individual milking. We hypothesized that milk composition would be affected by sampling technique and that milk fat would increase within a milking. Milk samples were collected from 4 Thoroughbred mares at 7 d postpartum in 3 ways: during natural milk let down while the foal nursed (>50 mL), stripping a residual sample between nursing bouts (15–20 mL), and total evacuation of the udder after muzzling the foal for 2 h. Samples were collected at the same time of day to avoid diurnal variation. Changes in composition within a milking were evaluated by muzzling the foal for 2 subsequent 2 h intervals then allowing the foal to nurse one side of the udder while milking the opposite side. The first 2 h milking was used to calculate fractions of the total volume collected. During the second milking, milk was collected into separate containers to represent the following fractions of the total collection: 10%, 25%, 50%, 75% and 100%. Milk fat, protein, and carbohydrates were measured using an infrared-based milk analyzer (MilkoScan FT+, Foss, Denmark). Effects of sampling technique and milk fraction on milk composition were evaluated using mixed model ANOVA with repeated measures (SAS 9.4). Milk fat was affected by sampling technique ( P < 0.0001). Residual samples had the highest concentration of milk fat (2.83 ± 0.13%), the total evacuations had the lowest milk fat (1.32 ± 0.13%), and the milk collected during let down was intermediate (2.13 ± 0.13%). Milk carbohydrates tended to be higher in total evacuations compared with residual or let down samples ( P = 0.067). There was no difference in milk protein between sampling methods ( P = 0.803). Milk fat increased through the duration of an individual milking ( P = 0.0002). Fat was the lowest in the first 10% of the total milk collected (0.976 ± 0.20%) and increased to 2.53 ± 0.20% in the last 25% of the collection. The concentration of milk protein and carbohydrates were similar between milking fractions ( P > 0.05). Milk composition is affected by sampling technique. Collecting a sample during active milk let down may be more representative of the milk composition the foal is consuming. Additionally, changes in milk fat during an individual milking followed a similar pattern as other species; milk fat increases through the duration of a milking while carbohydrates and protein remains unchanged.