Variability in Holstein heifer heart-girth measurements and comparison of prediction equations for live weight.
Measurement of heart-girth (chest circumference) is commonly used to estimate dairy heifer body weight from previously derived equations or tables. In this experiment, variability of heart-girth measurements as they are taken in the field was analyzed to determine the standard deviation within a group of 26 Holstein heifers of various ages weighing 42-590 kg. Standard deviations were 2.19 cm among 26 observers and 2.74 cm within any one observer. Repeatability between two heart-girth measurements by an individual observer on the same animal using a blind heart-girth tape was >0.99. Correlation coefficients between two measurements by different observers using blind measuring tapes on the same animal also were >0.99, with 99% of total differences due to observer and heifer, indicating very little random variation. A second part of this study was the validation of the most recently derived equation to calculate body weight from heart-girth. The equation was validated with data sets from universities across the United States and field data collected specifically for this study. Experimental and field data comprised of heart-girth and body weight measurements upheld the previously derived equation and support its continued use. These results allow more precise interpretation of heart-girth data collected from field studies with Holstein dairy heifers and provide more complete validation of existing body weight-prediction equations.
Heinrichs
A J
AJ
Department of Dairy and Animal Science, The Pennsylvania State University, 324 Henning Building, University Park, PA 16802, USA. ajh@psu.edu
Erb
H N
HN
Rogers
G W
GW
Cooper
J B
JB
Jones
C M
CM
D000005:Abdomen / Q000033:anatomy & histology*; D000367:Age Factors; D000818:Animals; D001724:Birth Weight; D002417:Cattle / Q000033:anatomy & histology*; D005260:Female; D011237:Predictive Value of Tests; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity