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The effect of feeding hay containing high levels of molybdenum on reproduction in beef heifers Stephens, Lisa Anne

Abstract

The effects of feeding hay containing high levels of molybdenum on reproduction in beef heifers were investigated. Sixty Hereford and Hereford-cross beef heifers, approximately 6 months of age, were randomly assigned to one of five treatment groups: Treatment 1 (TR1): 1 mg/kg Mo, 16 mg/kg Cu; TR2: 6-8 mg/kg Mo, 16 mg/kg Cu; TR3: 6-8 mg/kg Mo, 6-8 mg/kg Cu; TR4: 30-40 mg/kg Mo, 60-80 mg/kg Cu; and TR5: 50-67 mg/kg Mo, 115-134 mg/kg Cu. Three main areas of reproduction were investigated: onset of puberty, estrous cycle characteristics and fertility (including pregnancy and post-partum reproduction). Onset of puberty was assessed through twice monthly ultrasound examinations to determine the presence of the first corpus luteum (CL) and blood sampling to measure the associated increase in progesterone (P4) levels (>1 ng/ml). There were no statistically significant differences between the treatment groups. Once the heifers were known to be cycling, estrus was synchronized to allow for comparisons between the length of the estrous cycle, diameters of the dominant follicle and CL and maximum P4 levels. There were no statistically significant differences except for cycle length in which mean cycle length in TR4 was significantly shorter than TR1 (p

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