Characterizing bovine adipocyte distribution and its relationship with carcass and meat characteristics using a finite mixture model1

Abstract

The appreciation of adipose tissue complexity has initiated a new era of multifaceted investigations that continue to provide findings in adipocyte biology, but quantitative descriptions of adipocyte distribution are lacking. The first objective was to develop a finite mixture model to model adipocyte bimodal distribution and to correlate these estimates with carcass and meat characteristics. A secondary objective was to demonstrate within-animal observed variability in adipocyte cellularity. Steers were finished on a high-grain diet (n = 14) or grass (n = 16). One 12-cm thick LM steak from each steer was collected during harvest. A probability density function was developed that partitioned the cell diameter population into small and large populations and described the relative proportions of cells for each animal in these 2 distinct populations. Five parameters were estimated through the finite mixture model: the means (μ(1) and μ(2)) and SD (σ(1) and σ(2)) for the small and large adipocyte populations, respectively, and a proportion parameter (p) describing the proportion of the distribution of the smaller adipocyte populations. The proportion parameter for all animals tended to be different (P = 0.07) between groups with the grain presenting a p of 22.5 ± 12.5% and grass 16.2 ± 4.7%. The μ(2) was correlated with yield grade (YG, P = 0.04), and σ(2) with final BW, HCW, dressing percentage, YG, and quality grade score (P = 0.01). When correlating these parameters with the sensory data, μ(2) and σ(2) were correlated with tenderness (P ≤ 0.05), σ(1) and p with juiciness (P ≤ 0.05), and p with overall palatability (P = 0.01). Adipocyte cellularity variability was measured by examining the results from 5 randomly chosen steers from each group (grain and grass). In this subset, the μ(1) and p ranged from 32.1 to 46.1 μm and 1 to 27% for grass-finished steers, and ranged from 33.7 to 41.0 μm and 10 to 48% for grain-finished steers. The μ(2) and (1 - p) ranged from 75.0 to 105.1 μm and 73 to 99% for grass-finished steers, respectively, and ranged from 84.8 to 124.0 μm and 52 to 90% for grain-finished steers, respectively. The finite mixture model provides a quantitative description of the distribution of adipocytes and contributes to explaining adipocyte biology. Adipocyte cellularity variability among samples within an animal is a topic that should be further evaluated, as well as its correlation with other factors, such as gene expression and hormone secretion.

Effects of supplemental chromium propionate and rumen-protected amino acids on nutrient metabolism, neutrophil activation, and adipocyte size in dairy cows during peak lactation

“…The distribution of adipocyte area values within each cow (from 5 randomly selected cows) was plotted to assess the normality of the population. In contrast to some previous reports demonstrating bimodal adipocyte populations in relatively obese animals (Cruz et al, 2012), adipocyte populations within animal were unimodal in this study. However, distributions were right-skewed because of small numbers of very large adipocytes.…”

The effect of supplementing rumen undegradable unsaturated fatty acids on marbling in early-weaned steers1

“…Beef cattle production profitability due to carcass characteristics is directly affected by adipose tissue and its quantity in different adipose depots (Cruz et al, 2012).…”

“…Inadequacies in beef marbling and quality grades were also reported as the number one quality challenge facing the beef industry (Smith et al, 2006). Those inadequacies have a direct negative impact on beef cattle production profitability (DiCostanzo and Dahlen, 2000;Hogan et al, 2009;Cruz et al, 2012). Therefore, the beef industry is investigating methods to improve carcass quality.…”

Cellularity Description of Adipose Depots in Domesticated Animals

“…Compared with simply calculating mean cell size and the total number of adipocytes, studies that deal with adipocyte distributions are better at explaining the mechanisms involved in fat development [78]. For this reason, various approaches to evaluating adipocyte size distributions have been put forward, e.g., lognormal distribution fitting [72], normal distribution mixtures [79] and combinations of exponential Figure 2. Relationship between the first mode, second mode and percentage small adipocytes and backfat thickness in the outer subcutaneous layer in brood sows (data after Abadía et al [67]).…”