Short communication: Comparison of 2 methods of assessing calf birth weights in dairy calves

The collection of calf birth weight on US dairies is not a common practice. Calf birth weight was collected on 3 dairies (2 Holstein herds and 1 Jersey herd) over a 6-wk period. All calf birth weights were collected less than 2h after birth. A total of 872 calves were weighed by a spring scale and their weight was also estimated using a hoof circumference tape, with both weights and sex recorded. The general linear models procedure (PROC GLM; SAS Institute Inc., Cary, NC) was used to estimate least squares means for spring scale birth weight along with sex of the calf and dairy. Calf spring scale versus hoof circumference-estimated birth weight was compared using the regression procedure (PROC REG; SAS Institute Inc.). Calf birth weight was also broken down into increments, and spring scale versus hoof circumference-estimated birth weight was compared by t-test. Bull calves had a heavier birth weight compared with heifer calves [36.7±0.4kg (n=450) vs. 34.6±0.4kg (n=422), respectively]. The dairy on which calves were born had a significant effect on calf birth weight [dairy 1: 36.8±0.4kg (n=204); dairy 2: 39.5±0.2kg (n=463); dairy 3: 25.9±0.4kg (n=205)]. When the spring scale calf birth weight was linearly regressed by hoof circumference-estimated birth weight, a significant relationship was observed, with an R² value of 0.91. For calves weighing less than 31.3kg, the hoof circumference tape overestimated calf birth weight compared with the spring scale. However, for calves that weighed between 31.3 and 44.9kg, no significant difference was observed between spring scale and hoof circumference tape-estimated birth weight. For calves weighing greater than 44.9kg, the hoof circumference tape underestimated birth weight compared with the spring scale. Collection of calf BW by spring scale or estimated by hoof circumference tape appeared to be comparable for most calves because most calves weighed between 31 and 45kg, but caution should be used for calves with a light or heavy birth weight.