Effects of ionophore feeding and anthelmintic administration on age and weight at puberty in spring-born beef heifers

• Published in: Journal of animal science Vol. 74; no. 4; p. 736
• Main Authors: Purvis, H.T. (Oklahoma State Univ., Stillwater.), Whittier, J.C
• Format: Journal Article
• Language: English
• Published: United States 01.04.1996
• Subjects: ADDITIF AUX ALIMENTS DES ANIMAUX; ADITIVOS DE PIENSOS; AGE; Aging - drug effects; Aging - physiology; Animals; Anthelmintics - pharmacology; Body Weight - drug effects; Body Weight - physiology; BOVIN DE BOUCHERIE; Cattle - blood; Cattle - physiology; DIETA; EDAD; EFFICACITE ALIMENTAIRE; EFICIENCIA DE CONVERSION DEL PIENSO; ENSILADO; ENSILAGE (PRODUIT); EPOCA DE APAREAMIENTO; Feces - parasitology; Female; Fertilization - drug effects; Fertilization - physiology; GAIN DE POIDS; GANADO DE CARNE; GANANCIA DE PESO; GENISSE; GRAINE DE COTON; HELMINTHE; HELMINTOS; Ionophores - pharmacology; IVERMECTINA; IVERMECTINE; MADUREZ SEXUAL; MAIS; MAIZ; MATURITE SEXUELLE; MONENSIN; MONENSINA; NOVILLA; OVULE; OVULO; Parasite Egg Count - veterinary; PERFORMANCE DE REPRODUCTION; PESO; POIDS; Pregnancy; Pregnancy Rate; Progesterone - blood; Random Allocation; REGIME ALIMENTAIRE; REPRODUCTIVIDAD; RESIDU DE RECOLTE; RESIDUOS DE COSECHAS; SAISON D'ACCOUPLEMENT; Seasons; SEMILLA DE ALGODON; Sexual Maturation - drug effects; Sexual Maturation - physiology; VACA; VACHE
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/1996.744736x

Two hundred eighty-eight heifer calves in two 1-yr replications were used to test the hypothesis that ionophore (ION) feeding, anthelmintic (ANT) administration, or the combination (COMB) would cause heifers to express pubertal estrus at a younger age than control (CONT) heifers. Heifers were assigned randomly within three weight blocks in a randomized complete block design with a 2 X 2 factorial arrangement of treatments. A high-fiber diet was fed for 172 d during yr 1 (Y1) and 199 d during yr 2 (Y2). Monensin sodium (200 mg.animal-1.d-1) was fed to ION and COMB treatments and ivermectin (200 micrograms/kg of BW) was given to ANT and COMB groups at weaning and 84 d later. Rate of gain was monitored every 21 d and diet intake was adjusted to obtain equal rates of gain across treatments. Fecal samples were collected from one-third of the heifers in each group and analyzed for internal parasite egg counts every 21 d. Serum progesterone samples taken twice weekly were used to estimate onset of puberty. There was no treatment X year interaction in any parameter measured and the data were pooled across both years. Total weight gain was similar (P 0.10) for all treatments. Fecal egg output decreased (P 0.01) after initial application of anthelmintic. The ANT, ION, and COMB heifers had greater (P 0.05) gain:feed ratios than did CONT (.132, 0.142, and 0.148 vs 0.125 kg for ANT, ION, COMB, and CONT, respectively). Age and weight at puberty were different (P 0.05) for ION (425 d, 351.8 kg), COMB (425 d, 349.5 kg), and ANT (424 d, 348.8 kg) compared with CONT (433 d, 362.5 kg). There was no difference (P 0.10) in age and weight at puberty between COMB, ION, or ANT heifers. During Y1, but not Y2, there were a greater (P 0.05) number of COMB, ION, and ANT heifers pubertal before the breeding season. Additionally, there was a tendency (P