The effects and mechanisms of action of nutritional changes, differential suckling intensities and time postpartum in causing ovulation failure and ovarian acyclicity in beef cattle
Undernutrition and suckling effects on reproductive performance in cattle were investigated. It was therefore, the aim of this study to (1) evaluate reproductive parameters that were to be used in assessing reproductive function in heifers and postpartum cows; (2) to assess the effect of undernutrition and realimentation on ovulation and ovarian cyclicity in beef heifers; (3) to assess the effect of suckling intensity alone or in combination with undernutrition and the time postpartum in delaying reinitiation of ovulation in lactating beef cows. The results of this experiment showed that following the reduction in feed intake to half maintenance requirements there were four different types of changes in ovarian cyclicity recorded in the ten heifers. Group 1. Three heifers (No.1, 2 & 3) became acyclic without going through an oestrous cycle. Group 2. Four heifers (No. 4, 5, 6 & 7) went through one normal oestrous cycle each before becoming acyclic. Group 3. One heifer (No. 8) underwent two normal oestrous cycles before becoming acyclic. Group 4. Two heifers (No 9 & 10) continued to cycle without becoming acyclic. One of these two heifers (No. 9) had four short oestrous cycles of 8, 9, 11 and 11 days while No. 10 had three short oestrous cycles of 10, 12 and 12 days. During nutritional acyclicity there were no increases in LH concentration over the basal concentration following naloxone challenge irrespective of the dose used. During undernutrition, one heifer (No. 8) failed to exhibit an oestradiol-induced LH surge while the two heifers (NO. 9 & 10) exhibited a oestradiol-induced LH surge. There were no LH surges following PRID withdrawal in nutritionally acyclic heifers.