The effect of pituitary extract on the secretion of milk in the cow

Ott and Scott (1), Schäfer and Mackenzie (2), Mackenzie (3), and Hammond (4) are agreed that the intravenous, intramuscular or subcutaneous administration of pituitary extract (posterior lobe) to lactating animals causes a marked increase in the rate of secretion of the mammary gland. The effect appears within twenty or thirty seconds after injection and lasts for three or four minutes.

In order to find out what effect the extract might have on the total quantity of milk per diem and on its quality Gavin (5) experimented with dairy cows under ordinary farm conditions; he found that there was no change either in the amount or in the composition of the milk for the twenty-four-hour period.

We 1 have found that in the goat, within fifteen minutes after the injection, there is invariably an increase in the quantity of milk obtained and likewise in the percentage of fat. This has also been observed by Hammond. In one of our experiments the fat reached the high figure of 18 per cent. in the milk yielded after injection, while the normal for this animal was about 5 per cent. There is, however, a diminution in the quantity of milk obtained at the next milking period but the fat content remains above the normal for a day or two. The solids-not-fat of the milk do not appear to be affected.

The experiments which we desire to report on this occasion were made on the cow. Two animals at different periods of lactation were used. They were milked by hand, twice a day, at 6 a.m. and 5 p.m., and records were kept of the amount yielded and the percentage of fat for some days before and after the injection, as shown in the following tables: