# Heart Girth as a Predictor of Body Weight in Lactating Cows

## TL;DR

This study shows that heart girth can reliably predict body weight in lactating dairy cows, including locally adapted breeds in northern Italy.

## Contribution

The study provides breed-specific equations for estimating body weight from heart girth in lactating Holstein, Simmental, and Rendena cows.

## Key findings

- Heart girth strongly correlates with body weight across all three breeds of lactating cows.
- Models adjusted for days in milk and parity provided the highest accuracy for body weight prediction.
- Holstein and Simmental cows showed the highest accuracy in body weight estimation using heart girth.

## Abstract

Body weight is an important characteristic of dairy cows, with practical relevance for research and on-farm management. However, large-scale direct measurements are often difficult to collect under commercial farming conditions. Information on simple methods for estimating body weight in lactating cows is still limited, especially for locally adapted breeds. This study aimed to evaluate the use of heart girth as an indicator of body weight in different dairy cow breeds. The study involved lactating Holstein, Simmental, and Rendena breeds reared on farms in northern Italy. Body weight and heart girth were measured on the same day, and their relationship was evaluated using linear and nonlinear regression models. A strong association between heart girth and body weight was observed across all breeds, indicating that heart girth can be used as a reliable indicator of body weight in lactating dairy cows.

Body weight (BW) is an important trait in dairy cows; however, large-scale direct measurements are challenging. Heart girth (HG) has been proposed as a practical indicator of BW, but limited information is available for lactating cows, especially for locally adapted breeds. This study aimed to develop equations to estimate BW from HG in lactating Holstein, Simmental, and Rendena cows. A total of 293 cows (94 Holstein, 52 Simmental, and 147 Rendena) were selected from 6 farms equipped with an automatic milking system located in northern Italy. Both HG and BW were recorded on the same day, with HG measured using a tape and BW using a scale integrated into the automatic milking system. For each breed, linear, quadratic, and cubic regressions of BW on HG were tested, adjusting for days in milk and parity effects. The coefficient of determination and the root mean square error were reported. The best predictive performance was obtained with models adjusted for both days in milk and parity, with the highest accuracy achieved for Holstein and Simmental cows. These results corroborate that HG is a reliable predictor of BW in lactating cows of these breeds.