Beef cattle nutrition and physiology researchers have long been studying the regulation of marbling, because intramuscular (IM) fat deposition affects the meat quality and carcass value, researchers Tiago B. Freitas and Tara L. Felix with Pennsylvania State University, Wayne Shriver and Alejandro E. Relling with The Ohio State University and Francis L. Fluharty with the University of Georgia wrote in a recent edition of Translational Animal Science.
Freitas et al. pointed out that corn processing changes the digestion site of corn and that diet -- as well as its interactions with the site of absorption -- affect how and where adipose tissue grows.
However, the researchers noted that what regulates the dietary effect on each adipogenic site is not known. They added that while the glucose-dependent insulinotropic polypeptide (GIP) hormone has been studied for more than four decades in humans and other species, considerably less is known about the secretion and actions of GIP in ruminants, specifically the influence of GIP on lipid metabolism and the effect of GIP on IM fat deposition in beef cattle.
This led them to conduct a trial to evaluate the association between corn processing, GIP concentration and IM fat deposition.
Freitas et al. hypothesized that steers fed whole shelled corn (WSC) would have greater IM fat deposition than steers fed cracked corn due to an increase in plasma GIP concentration.
The researchers used backgrounded, Angus-cross cattle with an initial bodyweight of about 279 kg in a randomized complete block design in a feedlot setting for an average of 230 days. Cattle were allotted to 12 pens, with six pens per treatment and eight animals per pen. There were three blocks: heifers, small steers and large steers.
Two pens within each block were randomly assigned to one of the following treatments: (1) cracked corn or (2) WSC.
According to Freitas et al., average daily gains (P = 0.57) and final bodyweights (P = 0.34) were similar, regardless of treatment, but cattle fed cracked corn had reduced (P < 0.01) dry matter intake (DMI) compared with those fed WSC. This lesser DMI resulted in improved gain:feed ratios (P < 0.01) for cattle fed cracked corn compared with cattle fed WSC, the researchers said.
Freitas et al. noted that there was no effect (P < 0.33) of corn processing on plasma glucose, plasma GIP concentrations, hot carcass weight, dressing percentage or marbling score. However, there was a positive linear relationship (P = 0.03) between the IM fat concentration and plasma GIP concentration.
The researchers concluded that feeding cracked corn in feedlot settings decreases DMI without affecting ADG and, therefore, increases the gain:feed ratio compared with WSC. Additionally, they said corn processing did not affect the plasma GIP concentration but noted a positive association between the plasma GIP concentration and IM fat deposition.
Freitas et al. pointed out that these data do not confirm that GIP increases marbling accretion or decreases IM fat lipolysis as it does in subcutaneous adipose tissue, but more research is needed to evaluate dietary effects on plasma GIP concentration and its association with marbling.