The effect of feeding hay containing high levels of molybdenum on reproduction in beef heifers

• Main Author: Stephens, Lisa Anne
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/10012

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<0.05), although still within the normal range. Fertility was assessed by comparing conception rates after artificial insemination. There were no significant differences in conception rates, number of inseminations required for pregnancy, gestation length, calving rate or calf birth weight between the treatment groups. Four weeks after calving, weekly ultrasound examinations were done and blood samples were taken to determine the presence of the first post-partum CL and associated P4 levels to determine the length of the post-partum anestrus period. There were no statistically significant differences between the treatment groups. After the resumption of estrous cycles, superovulation and embryo recovery were used to assess post-partum fertility. There were no significant differences in superovulatory response, ova recovery or embryo quality between the groups. On three occasions during the study, liver biopsies and blood samples were taken to monitor Mo and Cu concentrations. Although there were significant differences between the treatment groups, the levels of Mo and Cu appeared to reflect the intake level of each group. There did not appear to be any interactions between Mo and Cu. Only when an ancillary experiment was done in which heifers were fed inorganic Mo and additional S were any symptoms of molybdenosis encountered. Therefore, it is concluded that high Mo hay can safely be fed to beef heifers without any adverse effects on reproduction. [Scientific formulae used in this abstract could not be reproduced.] === Land and Food Systems, Faculty of === Graduate