Deposition rates and accretion patterns of intramuscular fat, loin muscle area, and backfat of Duroc pigs sired by boars from two different time periods

¹ Department of Animal Science, Iowa State University, Ames 50011

^* To whom correspondence should be addressed. E-mail: tjbaas{at}iastate.edu.

	Abstract

A study was conducted to evaluate differences in performance, carcass composition, and deposition rates between purebred Duroc pigs sired by boars currently available and pigs sired by boars from the mid 1980s. Two lines were developed by randomly allocating littermate and half-sib pairs of females to matings by current (CTP) or old (OTP) time period boars. Pigs from 2 replications were weighed on test at a group mean live BW of 63.5 kg. Serial ultrasonic measurements of 10^th rib LM area (LMA), off-midline backfat (BF10), and intramuscular fat percentage (IMF) were collected every 2 wk in the first replication and used to assess deposition rate differences. Off-test ultrasonic LMA, BF10, and IMF measurements from a total of 557 pigs from 23 CTP sires and 232 pigs from 15 OTP sires across 2 replications and at a mean live BW of 109 kg were evaluated. All available barrows and randomly selected gilts (n = 277) were sent to a commercial abattoir and carcass measurements of 10^th-rib backfat (CBF10), last rib backfat (CLRBF), last lumbar backfat (CLLBF), and LM area (CLMA) were collected. Analysis of serial backfat measurements revealed a linear relationship between backfat and BW between 73 and 118 kg for pigs from both time periods. Pigs sired by OTP boars deposited more backfat (P < 0.05) at a faster rate than pigs sired by CTP boars over the entire test period. A curvilinear cumulative tissue deposition pattern was revealed for ultrasonically estimated LMA and IMF within both time periods. Significant linear and quadratic regression coefficient differences between lines indicate that pigs sired by CTP boars deposited more LMA and less IMF per kg of BW gain than pigs sired by OTP boars. Pigs sired by CTP boars had more LMA and less BF10 (P < 0.05), while pigs sired by OTP boars had more IMF (P = 0.04). Carcass evaluation revealed more (P < 0.01) CLMA and less (P < 0.05) CBF10, CLRBF, and CLLBF for pigs sired by CTP boars. No difference (P > 0.05) between the 2 time periods was found for ADG over the entire test period. Results from this study illustrate that significant progress in carcass composition has been realized within the Duroc breed since the mid 1980s. Long term selection response in carcass leanness has also resulted in changes in deposition rates of correlated traits such as LMA and IMF.

Key Words: carcass, deposition, leanness, performance, selection, swine

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