Short-term supplementation with maize increases ovulation rate in goats when dietary metabolizable energy provides requirements for both maintenance and 1.5 times maintenance.

This study aimed to evaluate ovarian follicular dynamics in goats submitted to synchronization of estrus and supplemented with diets that differed in the metabolizable energy source and amount of energy. The experiment was carried out using 42 does allocated into three treatments, fed for 9 days with a ration providing 1.0 times maintenance containing maize (1 MM, n = 14) or without maize (1 M, n = 14) or a ration providing 1.5 times maintenance containing maize (1.5 MM, n = 14). Estrus was synchronized with two injections of cloprostenol given 7 days apart. Does were also treated with intravaginal progesterone inserts and eCG. The number of ovulations and size of the follicles were measured using ultrasonography on Days 10, 11, and 12 after the start of the dietary treatment. The interval to estrus and duration of estrus did not differ between treatments (P = 0.382). Does fed with 1 and 1.5 MM had a similar number of ovulations but a greater number of ovulations than goats fed with 1 M (P = 0.028). The mean number of small, medium, large, and total number of follicles on Days 10 to 12 of ultrasound evaluations did not differ (P = 0.204) between treatments, but mean numbers changed over time (P < 0.001). The mean frequency and amplitude of LH pulses and concentrations of glucose, insulin, leptin, and insulin growth factor-1 in plasma were not significantly affected (P > 0.258) by any of the treatments. In summary, the inclusion of maize in the ration can stimulate ovulation rate at maintenance level. Similar results between groups fed diets that included maize and provided metabolizable energy at 1.0 and 1.5 maintenance demonstrate that to increase the ovulation rate when synchronizing estrous cycles in does, dietary supplementation with maize can be restricted to provide a maintenance level of metabolizable energy only, which would reduce dietary costs.

Use of GnRH agonist implants for long-term suppression of fertility in extensively managed heifers and cows.

The ability of gonadotrophin releasing hormone (GnRH) agonist implants to suppress ovarian activity and prevent pregnancies, long-term, was examined in heifers and cows maintained under extensive management. At three cattle stations, heifers (2-year-old) and older cows (3- to 16-year-old) were assigned to a control group that received no treatment, or were treated with high-dose (12 mg, Station A) or low-dose (8 mg, Station B and Station C) GnRH agonist implants. The respective numbers of control and GnRH agonist-treated animals (heifers + cows) at each station were: Station A, 20 and 99; Station B, 19 and 89; Station C, 20 and 76. Animals were maintained with 4% bulls and monitored for pregnancy at 2-monthly intervals for approximately 12 months. Pregnancy rates for control heifers and control cows ranged from 60-90% and 80-100%, respectively, depending on the study site. The respective number of animals (heifers + cows) treated with GnRH agonist that conceived, and days to first conception, were: Station A, 9 (9%) and 336 +/- 3 days; Station B, 8 (10%) and 244 +/- 13 days; Station C, 20 (26%) and 231 +/- 3 days. Treatment with high-dose GnRH agonist prevented pregnancies for longer (approximately 300 days) than treatment with low-dose GnRH agonist (approximately 200 days). In the majority of heifers and cows treated with GnRH agonist, ovarian follicular growth was restricted to early antral follicles (2-4mm). The findings indicate that GnRH agonist implants have considerable potential as a practical technology to suppress ovarian activity and control reproduction in female cattle maintained in extensive rangelands environments. The technology also has broader applications in diverse cattle production systems.