Study of Successive Experimental Lactations in Dairy Cows

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Abstract
Regrowth of the mammary gland with daily injections of 200 mg progesterone and 20 [mu]g estradiol benzoate for periods of 120 or 180 days followed by injections of 0.3 mg of estradiol benzoate per 100 lbs. body wt. for 14 days to initiate lactation was attempted in 19 lactating cows. In no case did the milk yield following the second attempt approach the level of the first experimental lactation. The mean maximum average daily milk yield of the 19 cows following the second treatment was only 22.7% of that obtained after the first hormone treatment. The 14 day estrogen injection at the end of the 120 or 180 day estrogen-progesterone treatment stimulated a slight increase in milk yield in 6 of the 11 lactating cows ranging from 0.4 to 4.2 lbs. per day, whereas 6 of the 8 cows that were dry the last 30 to 60 days produced from 0.3 to 8.5 lbs. per day with a mean maximum daily milk yield of 3.2 lbs. per day for the group.

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