True digestibility of amino acids and protein in pigs with 13C as a label to determine endogenous amino acid excretion
1995
Arentson, R.A. | Zimmerman, D.R.
The objective of this study was to determine whether differential labeling of 13C occurs in pigs fed diets with different 13C abundances and, if so, to use 13C as a label to determine true amino acid digestibility. Forty-eight pigs averaging 10.5 kg BW were fed dietary treatments consisting of a corn-corn gluten meal-crystalline amino acid diet (C-CGM) and a wheat-soybean meal diet (W-SBM). The 13C abundance of the amino acid fraction (AAF) of the C-CGM and W-SBM diets averaged delta 13C -14.19 per thousand and -26.36 per thousand, respectively. Three pigs/treatment group were killed when groups averaged 10.6 (initial), 22.9, and 46.6 kg BW, and AAF of organs were analyzed for 13C abundance. Carbon 13 in empty body AAF increased (-18.14, -13.98, and -12.66 per thousand) with increasing body weight in pigs fed the C-CGM diet and decreased (-18.06, -22.78, and -24.76 per thousand) in pigs fed the W-SBM diet. Liver, small intestine, and longissimus muscle tissues showed similar trends. Each tissue had dietary treatment effects (P < .001) and dietary treatment X weight group (P < .001) interactions. Ten pigs averaging 55.0 kg BW from each treatment group were assigned to metabolism cages and fed at 0700 and 1900. Six of these pigs from each treatment group were implanted with T-cannulas in the ileum and given a 17-d recovery period. At 1900 on d 0 of the collection phase, pigs were switched to the opposite diet that contained chromic oxide. Digesta were collected from 1000 to 1400 and 2200 to 0200 on d 1, 2, and 9, and feces were collected on d 7 and 8. Additionally, the four pigs from each treatment group that were not implanted with cannulas were fed similarly and a pig was killed at 1200 and 2400 on d 1 and at 1200 and 2400 on d 2, and AAF of organs were analyzed for 13C abundance. By using 13C abundance of small intestine AAF as an index of endogenous protein label, ileal protein was partitioned into endogenous and undigested protein. True and apparent amino acid digestibilities for W-SBM were as follows: Lys 79.9, 73.7; Thr 79.2, 70.6; Ile 86.1, 81.6; and Phe 86.6, 82.4, respectively. True and apparent amino acid digestibilities for the C-CGM were as follows: Lys 85.0, 81.5; Thr 74.6, 66.7; Ile 90.8, 88.2; and Phe 89.4, 86.5, respectively. In summary, pig tissue protein was labeled with 13C according to diet, and 13C can be used to determine true amino acid digestibility.
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