89 Relationships Among Measures of Efficiency with Body Weight, Frame Score, and Body Volume in Lactating Multiparous Crossbred Beef Cattle

Abstract Sixty cows of varying frame scores (FS; 5.17 ± 1.38) were used to examine relationships between body size [BW, FS, and body volume (V)] and cow efficiency. Dry matter intake (DMI) and BW change were monitored over 64 days starting 1 month before bull turnout. Cows were fed a forage-based diet and DMI monitored using the Insentec system. Average BW (ABW; 662 ± 93.3 kg) was calculated by averaging 2-d beginning and end BW. Measurements (body length, hip height, hip width, and heart, mid, and flank girth) were collected at the beginning and end of the experiment and average V (628 ± 96.4 L) calculated. Calf BW was recorded at weaning (WW). Pearson partial correlations between body size characteristics and efficiency measures were determined using GLM (SAS) and the MANOVA/PRINTE statement. There was positive correlation (P < 0.001; r = 0.84, 0.74, 0.81) between DMI (kg) and ABW, FS, and V. There was a tendency for negative correlation (P = 0.08, 0.09; r = -0.24, -0.23) between DMI (% of BW) and ABW and V. There was positive correlation (P ≤ 0.05; r = 0.33, 0.28, 0.26) between WW (kg) and negative correlation (P < 0.001; r = -0.63, -0.57, -0.65) between WW (% of ABW) and ABW, FS, and V. There was positive correlation (P = 0.04; r = 0.26) between calf ADG and ABW, and a tendency for positive correlation (P = 0.09; r = 0.23) between calf ADG to weaning and FS. The observed correlations suggest that larger cows consume more kg of feed and wean heavier calves with greater ADG to weaning, whereas smaller cows tend to consume more feed as a percentage of BW and wean a greater percentage of cow BW. Further research is needed on the complex relationship between cow size and efficiency.