537. The composition of sow's milk during the course of lactation

1. The composition has been studied of the milk of forty-four sows in the course of sixty-eight lactations. The milk was obtained by machine milking following intravenous injection of oxytocin. 2. Definite lactational trends have been observed for all the major constituents, and the third week seems a critical stage for most of the milk components. 3. The mean values for the milk, based on the analyses of over 450 samples from the seventh to fifty-sixth day of the lactation were: fat 9·58 %, protein 6·11 %, lactose 4·62 %, ash 0·92%. Such figures are considered to be rather meaningless for most practical purposes, in view of the marked changes over the course of lactation. 4. The day-to-day variation in the composition of sow's milk has been studied. Whereas the fat value changes considerably, the non-fat constituents show a less marked variation. Difficulties in securing a representative sample of the weekly milk have been overcome by preparing a composite sample from three milMngs within the week. 5. Some preliminary work has been done on variation in the composition during the process of milking. Sequential samples show an erratic fat content, especially during the early part of the lactation. When calculated on a fat-free basis, the protein, lactose and ash contents are relatively constant during the process of milking.