Environmental and genetic effects on calf linear measurements
Correlations between weight and linear measurements
Three linear measurements, height at withers, scapuloischial length, and heart girth, together with body weight were available for 403 calves at birth, 3 and 6 months; 306 at 9, 12 and 15 months; and 189 at 18, 21, 24 and 30 months. Analyses of variance laid out in Table 45 show the significance of effects on the linear measurements and weight from birth to 30 months.
The estimated least squares means for girth, height and length from birth to 30 months are given in Tables 46, 47 and 48. Table 38 lays out the corresponding least squares means for weight.
Figure 9. Mean changes in linear measurements and weight.
Figure 9 illustrates the mean changes in linear measurements and weight from birth to 30 months of age. The coefficient of variation of each of the three linear measurements at all stages was about 7%, while that of weight was around 17%.
Table 45. Analysis of variance of weight and linear measurements at ten different ages
Table 46. Estimated least squares means of girth from birth to 30 months (cms)
Table 47. Estimated least squares means of height to withers from birth to 30 months (cm)
Table 48. Estimated least squares means of the scapuloischial length from birth to 30 months (cm)
Table 49 presents the correlations between weight and height, length and girth. All were significant.
Table 49. Correlations between weight and linear measurements
Age 
No. 
Correlation between weight and 

Height 
Length 
Girth 

Birth 
403 
0.51 
0.52 
0.62 
3 months 
403 
0.61 
0.74 
0.85 
6 months 
403 
0.70 
0.76 
0.88 
9 months 
306 
0.40 
0.80 
0.90 
12 months 
306 
0.63 
0.80 
0.89 
15 months 
306 
0.36 
NA 
0.65 
18 months 
189 
0.79 
0.85 
0.91 
21 months 
189 
0.81 
0.83 
0.93 
24 months 
189 
0.77 
0.83 
0.91 
30 months 
189 
0.74 
0.85 
0.89 
NA = not available
The repeatability of calf linear measurements at birth, 3 and 6 months, considered as a characteristic of the cow, are indicated in Table 50.
Table 50. Repeatability of calf linear measurements
Age 
Height 
Length 
Girth 

r 
s.e. 
r 
s.e. 
r 
s.e. 

Birth 
.18 
.06 
.13 
.06 
.03 
.06 
3 months 
0 

.28 
.06 
.34 
.06 
6 months 
.30 
.06 
.28 
.06 
.37 
.06 
Heart girth is widely recognised as the most satisfactory single linear measurement for estimating body weight. An evaluation of its use at the 12 and 24 month stages is indicated in Table 51. The overall regression equations for calculation of 12 and 24 month weights obtained from the data in Tables 38 and 46 are:
12 month weight: 
y = 170.45 + 2.50 × 
24 month weight: 
y = 278.83 + 3.43 × 
The difference in the estimated weight and the actual weight recorded was calculated as a percentage of the actual weight for the 306 animals at 12 and 189 at 24 months of age. The number of animals whose weights were estimated to within two, five, and ten percent at each stage are presented in Table 51 together with the mean deviations and standard errors.
Table 51. Frequency of percentage differences in actual/estimated weights at 12 and 24 months.
Age 
Frequency 
Mean deviation (kg) 
SE of deviation 

<2% 
2  5% 
5 10% 
>10% 

12 m 
40 
91 
104 
71 
8.2 
0.4 
24 m 
32 
45 
55 
57 
15.5 
1.1 
At 12 months of age the estimated weight came within two per cent of the actual weight in 13% of the cattle (40 out of 306); to within five per cent in 43% of the cattle (40 + 91 out of 306); and to within ten per cent in 77% of the cattle (40 + 91 + 104 out of 306). At 24 months of age, the corresponding values were 17%, 41% and 70%.