The recording of 600 day weight performance for heifer calves provides very valuable information regarding both the heifers and their relatives. However, when heifers are being calved down at 2 years of age, they are often 5-6 months in calf by the time they reach 600 days.
The first 1/3 of pregnancy has relatively little effect on the heifer’s weight. Beyond that it starts to become significant, particularly in the last third, as can be seen from the table below.
| Breed | Additional Weight due to Pregnancy | |||||||
|---|---|---|---|---|---|---|---|---|
| 3 | 4 | 5 | 6 | 7 | 8 | 9 | (months) | |
| Bos Taurus (39kg calf) | 7 | 10 | 14 | 20 | 29 | 43 | 65 | (kg) |
| Bos Indicus (29kg calf) | 4 | 6 | 10 | 15 | 23 | 35 | 51 | (kg) |
Recording the 600 day weight performance for heifers that are in the later stages of pregnancy can cause significant errors as variation in live weight between heifers in a contemporary group may be incorrectly attributed to differences in their genetics for growth, whereas they may simply be at different stages of pregnancy.
Considerations for Breeders
As a general rule, weights from heifers more than 3 or 4 months in calf should not be submitted to BREEDPLAN. An exception to this would be for synchronised matings or short joinings, where only pregnancy tested heifers have been retained. If so, their weights are acceptable up to 5 to 6 months pregnant, as they will be at similar stages of pregnancy. Any slight bias will be in favour of early conceiving heifers.
BREEDPLAN can analyse 600 day weights that are taken on animals when they are between 501 – 900 days of age. So if, for example, a breeder wished to submit 600 day weights on heifers joined at 15 months (450 days), it would be preferable to take the weight when they are about 3 months pregnant i.e. 18 months (around 550 days), rather then going closer to the 600 days.
The stage of pregnancy does not have the same level of influence on the carcase traits so heifers can be scanned at any stage of pregnancy.
