# Serial Correlations of Partial Body Weight and Feed Intake in Crossbred Cattle

## TL;DR

This study determines how many days of data are needed to accurately measure feed intake in beef cattle, finding that 36 days are sufficient for 80% accuracy.

## Contribution

The study provides a novel estimate of test duration for feed intake accuracy without relying on part–whole relationships.

## Key findings

- A 36-day test period achieves 80% accuracy for mean feed intake in beef bulls.
- Partial body weight has a high serial correlation (r = 0.94), requiring little averaging for accurate estimates.
- Variation in feed intake serial correlation is not related to breed composition.

## Abstract

An applied question of importance in performance testing of beef cattle is the number of days for which data needs to be recorded in order to achieve a pre-specified accuracy of the mean, particularly for feed intake. However, many estimates of the necessary test period are based result from part–whole relationships between a short test period and a longer one. The objective of this study was to estimate the number of days required to produce a reasonably accurate record of feed intake individually fed beef bulls that does not rely on this part–whole relationship. The average serial correlation of daily feed intake (r = 0.10) was interpreted to suggest that a test period of 36 days was needed to achieve 80% average accuracy for the mean feed intake of an animal being evaluated. Because the serial correlation of partial body weight was very high (r = 0.94), there is little need to average values over days to achieve an accurate estimate of an animal’s partial body weight at any specific point in time.

Feeding behavior in cattle affects feed efficiency, which is important for increasing the profitability of production while simultaneously reducing the environmental impact. Over a six-year period, indigenous beef cows (Afrikaner, Bonsmara, Nguni) were crossed with indigenous and exotic (Angus, Simmental) sires in a hot and arid area, to produce 15 breed groups. After weaning, the bull calves were fed in a feedlot setting wherein daily feed intake and partial body weight were measured. The serial correlations of daily feed intake and partial body weight on consecutive days were estimated for each animal. Analyses of variance for the z-transformed serial correlations of daily feed intake and partial body weight were conducted. The linear model included the fixed effect of test group comprising pen and date at the beginning of the test and a fixed breed group effect. The average serial correlation of daily feed intake (r = 0.10) was interpreted to suggest that a test period of 36 days was sufficient to achieve 80% average accuracy for the animals being tested. The average serial correlation of partial body weight was very high (r = 0.94). Thus, there seems little need to average values over days to achieve an accurate estimate of the weight of an animal at any specific point in time. Variation among animals in the serial correlation of daily feed intake indicates differences in feeding behavior over time, but this variability was not related to breed composition. The results indicate that a test period of 36 days is sufficient to achieve 80% accuracy of the mean for daily feed intake of the animals being tested.