Pigs Fed 15 Ppm Skycis® (narasin) Have Similar Viscera Weight, Carcass Composition and Lean Quality Compared to Controls, but Prominent Gender Differences Exist in Carcass Composition: I

The objective of this study was to evaluate inclusion of Skycis^® (NAR) in the diets of pigs and determine the source of carcass yield, specifically dressing percentage, improvements observed in previous studies. Barrows (n = 50) and gilts (n = 50) of PIC C22 x 337 genetics were randomly assigned to a diet containing 0 (CON) or 15 ppm NAR initiated at 39.5 kg of body weight and continued until slaughter. Pigs (n = 47 barrows, n = 46 gilts) were slaughtered in two groups at which time individual organ weights were recorded. Full intestines were weighed, flushed and allowed to rest for 15 min and reweighed. At 24 h postmortem carcass composition and carcass quality data was obtained. At 48 h postmortem, one side of each carcass was fabricated into wholesale cuts according to North American Meat Institute specifications. Data points three standard deviations from the mean as determined by PROC UNIVARIATE were removed and remaining data was analyzed by using the PROC MIXED procedure of SAS 9.3. Barrows had more leaf fat by weight (P < 0.01) that made up a greater percentage of HCW (P = 0.03) compared to gilts. Mesentery fat (P = 0.02), full intestines (P = 0.02) and empty intestines (P = 0.05) were a greater percentage of HCW in barrows compared to gilts. Gilts had heavier spleens (P <0.01) that accounted for a greater percentage of HCW (P < 0.01) than barrows. No treatment differences were detected during the slaughter phase of the study except, pigs fed NAR had heavier (P < 0.01) hearts. Hot Carcass weights were numerically heavier (P=0.08) for NAR fed pigs compared to the control (101.93 vs 99.65 kgs). It should be noted that 3 NAR pigs exhibited intramuscular fat percentages (IMF) greater than 3 SD from the mean and their data was removed as outliers. Barrows carried greater weight in the gastrointestinal tract as both gut fill and tissue accretion but, this did not impact the overall yield of barrows. Increased metabolism simultaneously increases the mass of organs related to digestion. Pigs with greater intake will have heavier intestinal tracts compensating for increased consumption suggesting barrows in this study ate more. Pigs are largely being slaughtered at heavier weights allowing pigs to reach more advanced physiological maturity. Gilts are likely reaching puberty and cycling through estrus causing them to have decreased feed intake late in the growth curve and at the time of slaughter. The outlier pigs for IMF are of interest for future work with regard to the possible action of NAR on marbling fat accumulation.