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Length of Calving Interval and Average Milk Yield

Department of Dairy Husbandry, University of Illinois

ABSTRACT

Records published by Langmack (3) are considered with respect to the effect of length of calving interval on the average milk yield per day over the calving interval. The present data are confined to 186 Red Danish cows whose records in each case start with the cow's first calf and continue uninterruptedly through the nine following calvings, all ten calvings being normal, that is, no abortion. Yield is considered on an energy basis in terms of 4 per cent milk.

There is uniformly a negative correlation between calving interval and yield over the current calving interval, and a positive correlation between calving interval and yield over the following calving interval. Throughout, the relation is irregular and the correlation coefficients are small in value. When the several calving intervals (excluding the first because the influence of age on yield is most marked at this stage of life) are thrown together the correlation between calving interval and yield over the current interval is r = –0.134 ±0.018; that over the following interval, r = 0.142 ±0.018. Thus, while there is a small gain from a short calving interval in the current lactation it is very exactly lost in the following lactation.

The calving interval distribution shows a mean of 401 days, but with a pronounced mode between 350 and 370 days. If it should be desirable to shift the time of year of calving it appears that the calving interval may be prolonged to 18 months without adversely affecting the average yield per day, considered over both the current and following intervals.