Use of recombinant gonadotropin-releasing hormone antigens for immunosterilization of beef heifers.
The objectives of this study were to evaluate the effects of immunization against recombinant GnRH fusion proteins and growth promotants on onset of puberty, feedlot performance, and carcass characteristics of beef heifers. Heifers were immunized against an ovalbumin fusion protein containing 7 GnRH peptides (oGnRH, n = 12), a thioredoxin fusion protein containing 7 GnRH peptides (tGnRH, n = 12), a combination of oGnRH plus tGnRH (otGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant injected into the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk -2. Weekly blood samples were collected from wk -2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH-immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second booster injection, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from otGnRH heifers. During the 26-wk study, ovulation was prevented (P < 0.05) in 10 out of 12, 12 out of 12, 11 out of 12, and 0 out of 11 tGnRH, oGnRH, otGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH-immunized heifers than control heifers. Synovex H-implanted heifers had greater (P < 0.05) ADG from wk -2 to 26, greater LM area, and lesser percentages of KPH, yield grade, and quality grade than nonimplanted heifers, regardless of the immunization treatment. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented ovulation in 92% of the heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.
Postpartum ovarian function and fertility in beef cattle that produce twins.
A study was conducted to determine the effect of suckling on ovarian function and postpartum reproductive performance in beef cattle induced to produce twins by embryo transfer. This study involved 31 pluriparous Hereford, Angus and Hereford X Angus crossbred cows and 24 Hereford, Angus and Hereford X Angus crossbred heifers. Seventeen of the cows and 16 of the heifers calved twins, and the remainder produced single calves. From 45 d postpartum, the dams were exposed to three Hereford bulls until pregnancy was confirmed. The first postpartum ovulation was estimated from an increase in serum progesterone level. The interval to first postpartum ovulation was slightly, but not significantly longer for dams that calved and suckled twins than for dams that calved and suckled singles or calved twins and suckled singles (50.7 +/- 3.1, 43,5 +/- 3.4, and 37.7 +/- 5.6 d, respectively). This delay, however, did not significantly affect the number of days to conception for dams that suckled or calved twin or single calves. Once estrous cycles were initiated, the interval to conception for dams with twins was similar to that for dams with single calves. Under the management scheme used, postpartum ovulation and conception in beef heifers and cows were not significantly reduced by the production of twins.
P-fimbriae of Escherichia coli as carriers for gonadotropin releasing hormone: development of a recombinant contraceptive vaccine.
The demand for an effective and low cost means of fertility control of domestic animals has raised interest in the development of contraceptive vaccines. A promising candidate for a vaccine component is the brain peptide gonadotropin releasing hormone (GnRH), which plays a central role in the regulation of reproductive functions in vertebrates. Neutralization of GnRH by vaccine-induced antibodies is expected to prevent the reproductive activity in a wide range of species. A GnRH-protein conjugate was prepared by means of recombinant DNA technology. The oligonucleotides encoding GnRH were inserted in hypervariable regions of the subunit gene of P-fimbriae of Escherichia coli. Hybrid fimbriae encoded by the manipulated fimbrial gene clusters were expressed efficiently on the cell surface of Escherichia coli. Vaccination of female rats and bull calves with purified hybrid GnRH-fimbriae strongly affected the reproductive characteristics. We conclude that P-fimbriae represent a very attractive carrier system for application of GnRH in a new type of vaccine.