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Effect of Lasalocid on Growth and Puberal Development in Brahman Bulls^1,2,3,4,

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

Abstract

Twenty-four half-sib Brahman bulls (171 to 276 d of age; 140.9 to 243.2 kg) were paired by age and weight and randomly allotted to one of two treatment groups (12 bulls/treatment) with two replicates (six bulls/replicate). Control treatment (C) was a 4:1 corn (IFN 4-02-931):cotton-seed meal (IFN 3-01-621) diet fed at 1% of the average body weight plus Coastal bermudagrass hay (IFN 1-00-716) ad libitum. Lasalocid treatment (L) was the control diet with the addition of 200 mg lasalocid·head^–1d^–1. Lasalocid resulted in lower acetate and butyrate with higher propionate and no change in total ruminal volatile fatty acids. Lasalocid-fed bulls tended to gain more weight (L = 153.6 ± 8.5 kg, C = 138.4 ± 7.9 kg; P<.08), tended to have a greater average daily gain (ADG; L = .78 ± .05 kg/d, C = .71 ± .04 kg/d; P<.09) and had greater feed conversion (11.5% less feed/kg gain) than did the control bulls. Lasalocid did not affect bull height (HT), weight: height ratio, length (LE) or heart girth (HG) at any time tested during puberal development. Lasalocid bulls exhibited a greater increase in HG through 175 d on treatment (L = 27.6 ± 1.0 cm, C = 24.3 ± 1.8 cm; P<.05) and through first detected sperm (FS) in an ejaculate (L = 30.1 ± 2.2 cm, C = 26.1 ± 1.4 cm; P<.05), but the increase in HG from the start of the trial through puberty was not different between treatments. Bulls fed lasalocid also exhibited a greater growth in scrotal circumference (SC; L = 5.3 ± .7 cm, C = 3.1 ± 1.0 cm; P<.05) and in testicular volume (TV; L = 91.0 ± 21.9 cm³, C = 56.6 ± 12.4 cm³; P<.07) through 175 d of the trial and tended to have a greater SC (L = 24.4 ± .6 cm, C = 23.0 ± 1.1 cm; P<.10) and TV (L = 170.2 ± 16.7 cm³, C = 133.5 ± 16.2 cm³; P<.05) at detection of the first sperm. Scrotal circumference and TV were not different between treatments at puberty. Bull weight was not different between treatments at either FS or at puberty, but L bulls reached puberty at an average of 30 d before the C bulls (P<.06). It can be concluded from this study that addition of 200 mg lasalocid·head^–1d^–1 to a growing diet for young Brahman bulls improves feed conversion and decreases age at puberty.

¹ Journal paper TA 19446, Texas Agr. Exp. Sta.

² This study was a contribution to Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.

³ The authors thank R. J. Davis and J. Schenk for valuable technical assistance.

⁴ Reference to a company or trade name does not imply approval or endorsement by the Texas Agr. Exp. Sta.

⁵ Tom Slick Fellow.

⁶ Hoffmann-La Roche, Inc., Nutley, NJ.