1178
Weight, height and relative accuracy indicators as a management tool for reducing age at first breeding and calving of dairy heifers
In Québec, Canada, age at first calving occurs on average at 27 mo whereas the target is 22-24 mo to maximize herd profitability. The aim of this study was to generate indicators (such as heifer weight and height at 15 and 24 mo, and age at which optimal weight for breeding is attained i.e. 55% of mature weight) and their respective relative accuracy (RA) using a growth predicting model based on random regression. Weight and height data records from 1995 to 2012, respectively measured by chest girth, and height at the withers on Holstein (HO), Jersey (JE), and Brown Swiss (BS) dairy heifers were obtained from Valacta database (DHI agency, Ste-Anne-de-Bellevue, QC, Canada). Heifers with less than 2 records were excluded from the analysis. For each heifer, weight at 15 and 24 mo were computed using a second degree polynomial equation for which individual parameters were obtained from random regression using R (v1.15.2) and nlme package. For height, a non-linear mono-molecular random regression model was used. Age at optimal breeding weight was calculated by the square root of the second degree polynomial equation. Relative accuracy was calculated as the prediction error variance, relative to an RA of 99% when a heifer was measured routinely every 3 mo, starting at 2 mo of age. Table 1 shows the mean, standard deviation (SD) of the five indicators described above, RA and mature weight. It is possible to observe that, on average, dairy heifers in Québec, Canada could be bred at 13.6 mo, the optimal age for a first calving at 24 mo. These indicators could be calculated on an individual-heifer and on a herd-level basis, and used on farm as a management tool for reducing age at first breeding and at first calving.
Table 1. Indicators with their respective relative accuracy (RA, %)
Indicators |
HO |
JE |
BS |
||||||
Mean |
SD |
RA |
Mean |
SD |
RA |
Mean |
SD |
RA |
|
Weight at 15 mo (kg) |
425 |
34 |
87 |
297 |
26 |
92 |
379 |
36 |
87 |
Weight at 24 mo (kg) |
627 |
39 |
43 |
429 |
27 |
60 |
560 |
43 |
67 |
Height at 15 mo (cm) |
134 |
4.8 |
|
122 |
4.0 |
|
130 |
5.3 |
|
Height at 24 mo (cm) |
143 |
5.9 |
|
131 |
4.0 |
|
140 |
6.2 |
|
Age at optimal breeding weight (mo) |
13.6 |
1.4 |
|
12.7 |
1.4 |
|
14.5 |
1.7 |
|
Mature weight |
710 |
65 |
|
470 |
64 |
|
670 |
61 |
|
Keywords:
Dairy heifers
Age at first breeding
Age at first calving