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Dietary Alteration of Ruminal Fermentation on Efficiency of Growth and Onset of Puberty in Brangus Heifers^1,2,3,4,

Texas A&M University Agricultural Research and Extension Center, Overton 75684

Abstract

The influence of monensin and an altered roughage:concentrate ratio on age and weight at puberty was determined in 90 purebred Brangus heifers of known age and weight. The heifers were stratified according to weight per day of age and randomly assigned to a control diet of 80% alfalfa hay and 20% concentrates (C); C plus 200 mg monensin per head per day (M), or to a diet of 50% alfalfa hay and 50% concentrates (HE). Daily dietary intake of metabolizable energy (ME), crude protein (CP) and major minerals was similar for all diets and resulted in equivalent rates of daily gain (.60 kg per head per day) and similar increases in body condition score (3.46, where 1 = very thin and 10 = very fat). Analysis of volatile fatty acids (VFA) of the rumen fluid (molar %) at 3, 5 and 7 hr postprandial on day 80 of the trial showed an increase (P<.01) in propionate (C₃) due to M and HE treatments, and a reduction (P<.05) in acetate (C₂). Heifers with elevated ruminal propionate values (M and HE groups) reached puberty 29.5 days younger than controls (P<.009) and weighed 17.2 kg less (P<.03) than controls. It is concluded from these data that treatments which alter ruminal fermentation towards increased ruminal propionate production will decrease age at puberty in beef heifers.

¹ Journal Paper TA 14309, Texas Agricultural Experiment Station.

² The authors gratefully acknowledge Eli Lilly and Co. for their technical and financial support and the financial support and assistance of Chardo Pierce.

³ The authors gratefully acknowledge Premier Cattle Co. for supplying experimental animals and financial support.

⁴ Monensin (Rumensin®) Elanco Division, Eli Lilly and Co., Indianapolis, IN.

⁵ Research Scientist, Lilly Research Laboratories, Dallas, TX.