Lactic starter culture activity in milk from cows on rye pasture and in milk from cows on dry feed was compared, using two cultures widely distributed by commercial laboratories. The milk was pasteurized at 62.5°C. for 30 min. In 16 and 24 hr. at 21°C. one culture developed slightly higher acidities in milk from the pasture cows than in milk from the dry-feed cows, as shown by the means of 8 trials. The differences were statistically significant. On the other hand, the second culture, which showed lower activity in the test milks, developed a higher acidity in the milk from cows on dry feed. The differences at the 16-hr. period were statistically significant.
The total solids content of milk averaged 13.70% from the cows on pasture and 13.20% from those on dry feed. The proteose-peptone content varied but the mean value was about the same for milk from the pasture cows as for that from the dry-feed cows: 2.4 and 2.3 mg./10 ml. milk, respectively. Non-protein nitrogen averaged 4.5 mg./10 ml. milk from cows on pasture and 2.8 mg./10 ml. milk from cows on dry feed.
Although the differences in milk composition might have influenced lactic culture activity, it is considered that the effect of milk from cows on pasture depended on the characteristic of the lactic culture. Such effect appears to be of doubtful practical significance.
1Contribution No. 269, Department of Dairy Husbandry, and No. 44 Statistical Laboratory, Kansas Agricultural Experiment Station, Manhattan.