389 Proportionate mass of bovine heart, lung, and liver in response to animal mass.

Abstract Finished slaughter cattle increase in size by approximately 2.5 kilograms of additional carcass weight annually. Additionally, as cattle weights have increased, the frequency of late term mortality has increased concomitantly. Proportional size of the lungs and heart may affect risk of cardiovascular stress, and thus the ability of an animal to live and thrive. Our objective was to quantify the association of body mass and organ mass in cattle. Cattle (n = 2,030) were harvested in Canyon, TX, Amarillo, TX, Lubbock, TX, and Kuna, ID. Breeds of cattle varied; cattle included finished steers and heifers (n = 654), cull cows and bulls (n = 1,015), steer calves (n = 157), and fetuses (n = 204). Body mass (kg) was recorded immediately before or after immobilization. Fetal weights were recorded after evisceration of the dam and removal of amniotic sac. After evisceration, heart, lungs, and liver were separated and weighed. Data were subjected to regression analyses and used to identify the association between calculated empty body mass and mass of each organ (heart - HP; lung - LuP; liver - LiP) expressed as percentage of body mass. Body mass range varied (0.11 kg to 1,080 kg) due to the wide variation in life stages. Variability in percentage of organ mass for heart was moderately associated with body mass (Adj R² = 0.49; P < 0.01), conversely, lung (Adj R² = 0.88; P <0.01) and liver (Adj R² = 0.64; P < 0.01) mass were strongly associated. As body mass increased, percentage of organ mass decreased at an exponential (heart) or logarithmic (lung and liver) decreasing rate. The rate of change for HP was best estimated by the equation: HP = 0.70491e-0.00089x. The rate of change for LuP was estimated as LuP = -0.54180ln(calculated EBW, kg) + 4.08306. Moreover, the rate of change for LiP was estimated by the equation LiP = -0.43960ln (calculated EBW, kg) + 4.40514. Further analysis distinguished the cull and finished cattle populations. Finished cattle had lower proportions of heart (cull µ = 0.48%, fed µ = 0.40%, P < 0.01), lung (cull µ = 0.78%, fed µ = 0.52%; P < 0. 01), and liver (cull µ = 1.85%, fed µ = 1.31%; P < 0. 01) compared to cull cattle. These results suggest organ mass as a percentage of live bovine body mass decreases notably as cattle reach maturity, particularly for finished cattle. Specific to the cardiovascular system, proportional lung mass declined at a rate 3-fold faster than the heart. This data may provide insight into the stress placed on organs as cattle approach maturity.