The beef production system relies on each cow weaning a calf each year. There are many factors that determine the success of the cow weaning a calf. First of all the gestation length of a cow is around 283 days, leaving only 82 days for the cow to begin cycling again to then conceive by natural mating. In beef cattle this can be measured as inter-calving interval (the number of days between each calving). If the inter-calving interval exceeds 365 days then the cow is conceiving later in the mating period, reducing the time from birth of calf to weaning but also potentially reducing the chance of the cow conceiving next season.
International studies had reported a relationship between body condition score (BCS) and production traits, however, this had not been analysed in New Zealand cattle.
I presented this paper at the New Zealand Society of Animal Production conference in Rotorua in 2017. The aim of this research was to determine if BCS measured at different times of the year influenced the production traits of inter-calving interval, pregnancy diagnosis, birth weight, weaning weight and weaning rate.
Key Points
Cows of BCS ≥8 tend to have lower pregnancy rate than cows with BCS <8.
BCS at joining and pregnancy diagnosis influenced cow production.
Beef cows can lose BCS between winter and calving as this had a positive influence on inter-calving interval.
The animals used in this study were from Koromiko Farm in the Wairarapa. Records were collected from November 2012 to March 2015. The breed of the cows were Angus and Angus crossbred. They were managed as a commercial farm with heifers first bred at 15 months of age and non pregnant cows were culled after pregnancy diagnosis.
BCS in beef cattle is a visual score measured on a 1-10 point scale. The BCS measurements were taken four times annually at joining/rebreeding (November), pregnancy diagnosis/weaning (March), winter (June) and calving (August).
Weaning age was calculated as time in days from birth to weaning. Weaning rate was recorded as either 0 (calf not present at weaning) or 1 (calf present at weaning) for cows which were present at the winter BCS measurement.
BCS ranged from 3.5 to 9 (0.5 increments) which, after rounding up to the nearest whole number, were subsequently grouped into four BCS groups:
≤5
6
7
≥8
These groups were chosen based on distribution of BCS in the herd and to reflect the range of scores in the industry BCS targets.
Change in BCS was calculated as the difference among the four BCS groups and categorised as:
BCS increase
maintain BCS
BCS decrease
The first graph shows the differences in pregnancy rates (%) between the BCS groups at joining and pregnancy diagnosis BCS measurements.
There was no difference in pregnancy diagnosis between the BCS groups at the joining BCS measurement (blue bars).
There was a slight difference in BCS at pregnancy diagnosis (purple bars), in that the pregnancy diagnosis was lower in the cows that were greater than BCS 8 at pregnancy diagnosis compared with cows that were a BCS 7, 6 or ≤5.
This means that it will be best to keep cows below BCS of 8 at pregnancy diagnosis.
There was a difference in birth weights of the calves between the BCS groups at the Joining BCS measurement (Graph 2). The cows that were BCS of 6, had lower birth weight calves than cows with a BCS of 7 or greater.
This means that the cows of slightly greater BCS at joining are likely to have heavier calves at birth.
The effect each BCS group at each BCS measurement period, joining, pregnancy diagnosis, winter, calving and re-breeding, can be found in the full paper, however, there were no differences found between the remaining production traits of weaning weight and only BCS at pregnancy diagnosis influenced weaning rate.
The next two graphs are the groups of BCS change to show if an increase, decrease or maintenance of BCS had any effect on the cow production.
A decrease in BCS from winter to calving resulted in cows with a shorter inter-calving interval than that of cows which increased in BCS or maintained BCS as shown in the graph above. This could be a result of the cow using the energy reserves towards the foetus and also being a lower BCS could result in less complications at calving resulting in a shorter period between calving and conception (re-breeding).
Either way, this result looks like it is a good thing if cows are losing condition to calving. Keeping in mind that the majority of cows in this herd are already in good condition (BCS 5-8).
Weaning rate and birth weight were not influenced by change in BCS. However, a decrease or no change in BCS from joining to pregnancy diagnosis resulted in 18 kg greater calf weaning weights compared with those of cows that had increased BCS as can be seen in the graph above.
In summary, for the BCS in this herd there was a benefit to having the cows in greater BCS at joining for greater calf birth weights and the other BCS measurement periods were less important. The cows can reduce in BCS between winter and calving as this had a positive influence on inter-calving interval.
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