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Milk yields of goats milked twice daily at 16/8 h intervals or 12/12 h intervals were equal. In goats normally milked twice daily at 16/8 h intervals, one mammary gland was milked thrice daily for one week while the other continued to be milked twice daily. This was done at 3, 7, 16, 24 and 33 weeks of lactation. Feeding level was maintained during these experiments. At every stage of lactation, thrice-daily milking increased milk yield (by about 8%). Stage of lactation had no effect on the size of the response. Yields of each gland increased by as much in an experiment involving thrice-daily milking both glands. Milk yield increased as soon as thrice-daily milking was started, and decreased towards normal values as soon as twice-daily milking was resumed. Milk composition during thrice-daily milking was unaffected with respect to concentrations of Na+, K+, Cl-, lactose, protein, fat and citrate. There was no change in milk yield of the gland which continued to be milked twice daily. The stimulatory effect was entirely local to the gland receiving the extra milking. Milk secretion rate during the 16 h period which included the extra milking was significantly higher during thrice-daily than during twice-daily milking; secretion rate during the rest of the day was unaffected. There were significant diurnal variations in secretion rate during thrice-daily milking such that the secretion rate during the 23.00-07.00 h period was highest and the secretion rate during the 07.00-15.00 h period was the lowest.(ABSTRACT TRUNCATED AT 250 WORDS)
Henderson et al. (Mon,) studied this question.