Evaluation of the compositional growth and predicted lysine requirements of pigs by three sire lines

Abstract Text: Barrows and gilts (n=240) from three sire lines were collected to parameterize their BW and compositional growth and predicted daily lysine requirements.  Pigs were weaned at 21 d of age with 4 pigs per pen (1.12 m²) in grow-finish.  Grow-finish diets were fed in 6 phases with the first 5 phases fed for 21 d each and the final diet fed until marketing.  Pigs were weighed at 21, 28, 35, 49, 56, 77, 98, 119, 140, and 161 d of age and close to target final BW of 145 kg. Pigs were measured via real-time ultrasound at each weigh day starting at 56 d of age.  An exponential function (Y= exp (b₀+ b₁ BW + b₂ BW²) was fitted to the serial ultrasound measurements of backfat depth (BF) and loin muscle area (LMA). Protein and lipid accretion rates were predicted from the serial ultrasound measurements  and used to estimate daily lysine requirements (NRC, 2012). Measurements were analyzed using Proc GLM of SAS with significance value of P < 0.05.  At 161d of age, sire line and sex affected BF (P < 0.001) and LMA (P = 0.035);  sire line 3 (SL3) pigs had less BF (1.27, 1.53, and 1.55 cm respectively)   and greater LMA (50.37, 48.67, and 49.64 cm² respectively)  than sire line 1 (SL1) and sire line 2 (SL2) pigs which had similar BF and LMA.  Gilts had less BF than barrows (P < 0.001) at each measurement time and the difference increased with age.  When adjusted for BW, the SL3 pigs had a much greater LMA at 161 d of age (52.45, 47.35, and 48.89 cm², respectively) and each other measurement time than SL1 and SL2 pigs. The growth of BF relative to BW gain (mm/kg) increased as BW increased.  The growth of LMA relative to BW (cm²/kg) was linear from 28 to 90 kg BW and then decreased as BW increased.  Daily SID lysine requirements increased from 30 to 50 kg BW, to nearly constant values from 50 to 100 kg BW (maximum value of 18.53 g SID Lys/d at approximately 70 kg BW), and then decreased as BW increased above 100 kg BW.  The daily Lys requirements for the barrows were 3.4% greater than the gilts.  Pigs by different sire lines and sex have different compositional growth and daily lysine requirements. 

Keywords: , pig growth, lysine requirements, backfat