The lactation curve of the cow at the ascending phase
Authors: Mäkelä Aarne 
Published: July 2018

Since the year 1947 daily milk yields of Ayrshire cows at the ascending phase have been obtained at the University Farm Viik. In this paper only healthy cows are considered. Because the yearly milk production has considerably increased since 1947, the milk records have been divided into three sequences: the first consists of the control years 1946-47 – 1949-50, the second 1950-51 – 1956-57 and the third 1957-58 — 1960-61. In each sequence average lactation curves have been drawn separately for heifer-cows and older cows in both the winter and pasture feeding periods. The lactation curves have been designed in such a way that both productions and the durations of the ascending phase or fixed fractions of them (1/8, 1/4, 1/2, 3/4, 5/4) are averages (Figures 1—3). The designing of these curves has been more thoroughly described in an earlier paper (12, p. 162). In the present paper attention has been paid to some of the factors influencing the lactation curve at the ascending phase. The following points were noted. The average peak production of cows older than heifer-cows at winter feeding was 21.8 kg in the first sequence, 26.0 kg in the second sequence, and 26.6 kg in the third sequence. At pasture feeding the corresponding figures were 21.6 kg, 20.8 kg, and 24.2 kg. The duration of the ascending phase at winter feeding in cows older than heifer-cows in the first sequence was on an average 31 days, in the second sequence 32 days, and in the third sequence 36 days. At pasture feeding the corresponding figures were 25, 28, and 33 days. The average peak productions as well as the average of the times involved in reaching them were higher at winter than at pasture feeding. The feeding in both periods was intensive during the second and third sequences. At winter feeding the duration of the ascending phase was generally longer in heifer-cows than in older cows. The lactation tangent at the ascending phase, which is the ratio between the peak production and the duration of the ascending phase (kg/day), was on an average lower in heifer-cows both at winter (about 0.5) and at pasture feeding (about 0.6) than in older cows (both at winter and pasture feedings 0.8—0.9). No significant difference was found in the values of lactation tangent at winter and at pasture feedings. The influence of the condition of the cows on the peak production and the duration of the ascending phase of cows older than heifer-cows is slight, assuming that the cows at parturition are in normal or good conditions. Heifer-cows in normal condition, on the contrary, do not have an average peak production as high as cows in good condition. The duration of the ascending phase of the heifer-cows in normal condition is, however, about as long as that of cows in good condition. Only a few cows in a thin condition were included in this study. The length of the dry period has no great influence on the peak production if the dry period is at least one month in length. A too short dry period before the second lactation has a detrimental effect on lactation. It was found that at winter feeding the mean production of the three first days in per cent of the peak production was smaller in heifer-cows (about 50 %) than in older cows (about 60 %). According to this, lactation in heifer-cows begins both absolutely and relatively more slowely than in older cows. There is a rather close correlation between the mean production of the three first days and peak production. At winter feeding in cows older than heifer-cows, the peak production can be predicted on the basis of the mean production of the three first days by the aid of the regression equation. The accuracy, however, will be only 5 or 6 kg if a reliability of 95 per cent is desired. There is a very close correlation between the production of the tenth day (the mean of the 9th, 10th, and 11th day) and peak production. At winter feeding in cows older than heifer-cows, the peak production can be predicted on the basis of the production of the tenth day either by the aid of the regression equation or by adding to the production of the tenth day the difference between the peak production and the production of the tenth day. The accuracy will be 4 kg for areliability of 95 per cent. In the two latter sequences the most probable value for the peak production can be found by adding 4 kg to the production of the tenth day.