AGE AT FIRST CALVING
A series of Articles over the next few Journals will look at how the
Centre for Dairy Information is turning our data into interesting analyses of the current dairy industry. Here, Henry Richardson explains the fi rst – how age at fi rst calving may refl ect on lifetime production
H
eifer calving age has long been regarded as a key measure of herd management
policy and effi ciency. It encompasses the crucial, but largely unproductive, rearing period of the animal. Nutrition and growth during this period are key to the heifer’s future earning capability.
This study aims to collate the earlier, well known, picture with the more recent trends and age at calving patterns achieved in today’s herds. Partly to discover how the current trends have changed in response to infl uences such as improved genetics and nutrition. Also to see if the results from the smaller populations studied in the more scientifi c works can be related to the wider UK picture.
Results
A - Heifer Calving Age in the 1980s
In all, records from some 192,000 UK-born animals were collated for this group. Only registered animals were selected initially, so that the results would be representative of the breed and not affected by cross- breeding or other infl uences. Records from individual
25% in qtr
40 THE JOURNAL JUNE 2010
2010 The Centre for Dairy Information.
www.thecdi.co.uk
24-26 months
Mean 29.9 mo
21% in qtr 32-34 months
animals were included where the registration details were present and marked as genuine, plus registered as UK-born (i.e. breed code 01 in UK milk recording terminology). Imported animals were excluded. First lactation calving dates were used to calculate age at calving (in months) for all animals who also had genuine (i.e. not estimated) dates of birth and calving. Calvings from a three-year period 01 January 1986 to 31 December 1998 were selected to reduce the effects any one season might have on the pattern revealed. No other selections or fi lters were applied. Chart [1] shows the pattern for the period, with the proportion of heifers calving at each age expressed as a percentage of the total in the group. There are two distinct peaks of calvings (a “bimodal” pattern in statistical terminology). The fi rst at around two years old includes one quarter of the total population in the three-month period from 24 to 26 months. A second, subsidiary peak, accounts for a further 21% of the total, in the period from 32 to 34 months. The inference being that heifers during this period were generally reared to either achieve two-year calving or come into the milking portion of the herd closer to three years old. Particularly relevant perhaps for herds aiming to exploit the seasonal milk pricing policies at the time, with production targeted to match peak pricing.
B - Milk Yields versus Calving Age 1986-1998
Throughout the 1980’s and early 90’s, the received wisdom was, with considerable justifi cation, that two-year calving was not only possible, but economically highly desirable, in order to reduce the expensive rearing period and thus increase overall economic effi ciency of the herd. This was further re-enforced by the improvements in the milk yields achieved by those fi rst-calf heifers over the same period, as illustrated in charts [2] and [3]. In the mid-80’s peak yields were being achieved by animals calving in the 32 to 35 month period, coinciding with the second peak of calvings seen at the same time. By the mid-late 90’s, heifers calving between 24 to 30 months were achieving yields much more comparable to the later calvers, thus reducing the yield penalty seen previously in the earlier calvers.
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