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Influence of Cottonseed Meal Supplementation and Cecal Antibiotic Infusion in Lambs Fed Low-Quality Forage. II. Serum Urea-Nitrogen, Insulin, Somatotropin, Free Fatty Acids and Ruminal and Cecal Fermentation^1,2,

New Mexico State University, Las Cruces 88003-0009

Abstract

Sixteen wether lambs (37 ± 3.7 kg) cannulated at the rumen and cecum were used in a 2 x 2 factorial experiment. Lambs were adapted for 15 d to a basal forage diet (50% prairie hay:50% oat straw; 5.8% CP) or basal plus 189 g · head^–1 · d^–1 of cottonseed meal (CSM; 42.5% CP). Starting on d 16, lambs in each diet group were infused via cecal cannulas with 2 g neomycin sulfate or .15 M NaCl. On d 24, ruminal, cecal and blood samples were taken at –2, 0, 1, 3, 6, 9, 12, 16, 20 and 24 h after CSM supplementation. Supplementation increased (P < .10) serum insulin and decreased (P < .10) somatotropin, but it had no effect on serum free fatty acids. Cecal antibiotic infusion decreased serum free fatty acids (P < .05). Protein supplementation increased (P < .10) serum urea-N, and antibiotic infusion increased (P < .10) serum urea-N in supplemented, but not in unsupplemented, lambs. Supplementation increased (P < .10) cecal NH3 concentrations at 0, 6, 9, 12, 16 and 20 h, whereas antibiotic had no consistent effects. Antibiotic increased (P < .10) ruminal NH₃ at all times, except 12 and 20 h, in supplemented, but not in unsupplemented, lambs. Supplemented, antibioticinfused, but not supplemented, saline-infused, lambs had lower (P < .10) ruminal acetate (mol/100 mol) than either unsupplemented, saline or antibiotic-infused lambs at 3, 9 and 12 h. Supplementation with CSM increased cecal total VFA (P < .10) at all sampling times. Cecal acetate was higher and propionate lower (P < .10) at most sampling times in unsupplemented, antibiotic-infused lambs compared with lambs in other treatment groups. Cecal antibiotic infusion appeared to enhance N recycling in CSM-supplemented lambs but not in unsupplemented lambs.

¹ Journal article 1349 of the New Mexico Agric. Exp. Sta., Las Cruces 88003-0009.

² The authors thank Lilly Research Laboratories, Indianapolis, IN, for supplying the ovine insulin (615-1112B-108-I) used in the insulin assay. Appreciation is also expressed to the National Hormone and Pituitary Program for supplying the anti-ovine GH (NIADDK-anti-oGH-2; AFP-00123080) and the biologial (NIADDK-oGH-12; AFP-4015A) and iodination (NIADDK-oGH-I-3; AFP-5285C) grade ovine GH used to quantify serum GH. Gratitude also is expressed to Paula Ross, Dale Schickedanz and Boo Reynolds for clerical assistance, and to the Animal and Range Science Endocrinology Laboratory for hormone assays.

³ Present address: Dept. of Anim. Sci., Univ. of Missouri, Columbia.

⁴ Present address: College of Agric. and Home Econ., Texas A&I University, Kingsville.

⁵ Present address: Dept. of Anim. Sci., Univ. of Illinois, Urbana.

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