PSI-31 Retrospective analysis of growth performance and carcass ultrasound data of yearling bulls enrolled at the Cal Poly Bull Test

Abstract

Since 1956, the Cal Poly Bull Test has evaluated performance of yearling bulls in a multi-breed contemporary group in the western United States. The main objectives of this study were to evaluate the consistency of the relationship between growth and ultrasound traits and between the number of bulls selling and sale price over a 19-year period from 2001–2019. Out of 3,712 bulls, a total of 2,503 Angus and 453 Hereford bulls were used in the analyses using SAS. Bulls were sold in the following pre-determined breed categories; Angus Heifer Bulls, Multi-Trait Angus Bulls, Growth Angus Bulls, and Hereford Bulls. The breed × year interaction significantly (P < 0.01) affected sale price, scrotal circumference (SC), ultrasound ribeye area (UREA), ultrasound intramuscular fat percentage (UIMF), end weight, and average daily gain (ADG). Overall, Hereford bulls had significantly (P < 0.0001) lower ADG than Angus bulls. A positive relationship between ADG and UREA (P < 0.0001; r2 = 0.10) and between UREA and SC (P < 0.0001; r2 = 0.05) was observed. A significant, positive relationship (P < 0.01; r2 = 0.24) between end weight and REA was also exhibited. A significant breed × year interaction (P < 0.01) was observed for sale price, wherein Angus heifer bulls consistently sold for the highest price. Additionally, sale price analyses indicated a moderate, negative relationship (P = 0.02; r2 = -0.584) between number of animals entered in the sale and price. Consistently, Angus bulls had higher (P < 0.0001) sale prices. Sales with higher bull numbers were those with the lowest average prices. The year and breed category explained 31 and 22.5 % of the variance in the price, respectively. Growth performance and sale price may have a biological or genetic component as indicated by breed differences consistently over the 19-year period.