The effects of lysine and hormones on amino acid and glucose venous outflow in the skin and the whole body were determined in Angora wethers (n = 5). The goats had chronically catheterized superficial branches of the deep circumflex iliac artery and vein of each side. Four experiments involved the intra-arterial test infusion on one side (60 min) of lysine (0, 0.16, 0.8, 4 mg/h; Exp 1) alone and lysine (4 mg/h) together with infusions (60 min) of successively increasing doses of insulin (0, 0.1, 1 and 10 mU/h; Exp 2), cortisol (0, 0.15,1.5 and 15 g/h; Exp 3),and triiodothyronine (T₃), 0, 0.02, 0.2 and 2 g/h; Exp 4). The other side served as control and was infused with saline only (10 mL/h). Lysine concentrations in venous outflow from the control side (80.9 M) were unaffected by lysine infusion, whereas venous lysine concentrations in the test side were 82.1, 85.7, 96.9, and 109 M during infusion of 0, 0.16, 0.8 and 4 mg lysine/h, respectively. Although venous concentrations of insulin ( 22 U/mL) were similar (P>0.05) and unchanged in both sides for all doses of insulin infused, the highest dose of insulin infusion (10 U/h) decreased (P<0.01) lysine and glucose venous concentrations in the skin. Plasma variables were unaffected (P>0.05) by cortisol despite six to ten-fold increase in the plasma cortisol concentration. The highest dose of T₃ (2g/h) increased (P<0.02) T₃ from 250 to 450 ng/dL, decreased (P<0.01) plasma concentrations of the branched-chain amino acids (BCAA) by approximately 20 - 30% and phenylalanine concentrations by 80%, and increased (P<0.01) glucose concentrations by 36% equally in venous plasma on both perfused regions. These results suggest that whole body BCAA and glucose concentrations in Angora goats are highly responsive to doubling of physiological concentrations of T₃, but apparently unresponsive to acute (60 min) pharmacological increments in plasma cortisol concentrations. Knowledge of the interaction between nutrients and hormones in the skin will allow better ration formulation and development of local growth promotants.

The effects of methionine (Met), insulin, cortisol and triiodothyronine (T₃) infusions on amino acid and glucose venous outflow in the skin was determined in Angora wethers (n = 5). The goats had chronically catheterized superficial branches of the deep circumflex iliac artery and vein on each side. Successively increasing doses of Met, or constant doses of Met and successively increasing doses of hormones were intra-arterially infused for 60 min into one side of the goat. The other side served as a control and was infused with saline (5 ml/h). Infusion of 0, 0.2, 1, 5 and 10 mg/h of Met increased venous Met concentrations in the treated side (21.1, 22.1, 25.4, 38.4 and 15.7 M, respectively), whereas venous outflow remain unchanged (19.2 M)in the control side. Met infusion increased (P<0.05) venous plasma cystine concentrations in the treated side. Increasing levels of insulin (1, 10 and 100 mU/h) with constant infusion of Met (3 mg/h), reduced (P<0.01) plasma Met concentration in the treated side from 31.3 to 21.3 M across insulin infusions. Cortisol (0, 1.5, 15 and 150 g/h) had no effect on Met concentration. Following T₃ infusion (0, 0.1, 1 and 10 g/h), plasma Met concentration decreased (P<0.01) from 29.7 to 20.3 M across T₃ infusions. A corresponding reduction in Met concentration from 20.6 to 16.6 M was observed in plasma from the control side. Plasma concentrations of Cys, Val, Leu, Ile, Lys, Arg, Thr and Gly from both iliac veins were also decreased (P<0.05) as a result of T₃ treatment. The above results suggest that insulin regulates skin Met metabolism via local effects, whereas T₃ influenced amino acid metabolism via centrally regulated mechanisms. In Angora goats skin demand for Met may be higher than average blood Met concentrations.

Nutritional manipulation of mohair quality was investigated by measuring the effects of various intraperitoneal lysine doses on mohair quality and N metabolism in 18 mature Angora wethers. Animals were infused intraperitoneally with lysine (0, 1.18, 2.23, 3.35, 4.67, or 5.92 g day^-1) for 28 days. Lysine infusion decreased linearly the percentage of fibers that were medullated (R = 0.30; P = 0.0006). Fiber diameter (R = 0.16; P > 0.10) was not affected. However, several metabolic changes were observed when the highest doses (4.67 and 5.92 g) of lysine were infused, which may be indicative of an amino acid imbalance or toxicity. Plasma lysine concentrations increased quadratically (R = 0.51; P < 0.10) when lysine infusions exceeded 3.35 g lysine day^-1 and urinary N excretion increased (linear: R = 0.55; P < 0.02). DM intake, N absorbed, N retention, and N retention as a percentage of dietary and infused N, were not affected (P > 0.10) by lysine infusion. Plasma urea was elevated (linear: P < 0.015). The percentage of medullated fibers decreased linearly with increasing lysine content of the infusate. The infusate also caused accumulation of plasma lysine at infusions greater than 4.7 g lysine day^-1.

Eight mature Angora wethers (average BW 47.2 kg) were used in a 4 × 4 replicated Latin square design to evaluate responses to intraperitoneal (IP) administration of amino acids. The IP treatments consisted of saline (Control), methionine 1 g/d (Met), lysine 2 g/d (Lys), and methionine + lysine (Met + Lys). The amino acids dissolved in Control were infused continuously for the first 14 d of each 28-d period using peristaltic infusion pumps. Average d-28 grease and clean mohair yields (grams/100 square centimeters), and fiber diameter (micrometers), and length (centimeters) measurements during Control administration were 8.8, 7.6, 40, and 2.3, respectively. Mean clean mohair yield and fiber diameter increased by 5.3% (P < 0.039) and 2.5% (P < 0.067), respectively, with Met administration but were decreased by 9.2% (P < 0.033) and 3.8% (P < 0.001), respectively, by Lys administration; however, mean fiber length was increased (P < 0.014) 21.7% by Lys infusion. The goats did not exhibit increased grease (P > 0.939) and clean (P > 0.477) mohair yields and fiber diameter (P > 0.619) when treated with Met + Lys. A N balance trial was conducted during d 10 through 14 of each period. Total retained N (grams per day) during Control administration was 18.4 and 24% greater than Met (P > 0.281) and Lys (P < 0.061), respectively. When expressed as a proportion of N intake, retained N was lowest (P < 0.127) in the Lys infusion group. Jugular blood ammonia N and plasma glucose and total protein concentrations were not affected (P > 0.10) by treatment. Plasma urea N was 6.7% lower (P < 0.008) during Met + Lys treatment at 0 and 3 h after feeding than the Control group. Infusion of Met and Lys into the peritoneal cavity of Angora goats altered mohair yield by affecting mohair diameter and length.