Plasma LH, FSH, testosterone, and age at puberty in ram lambs actively immunized against an inhibin α-subunit peptide
Introduction
Development of a method to advance puberty in ram lambs may prove worthwhile by enabling younger males to be used in the breeding flock. Use of younger males may reduce production costs, accelerate benefits of genetic selection, and allow earlier progeny and libido testing. Benefits of advanced puberty in ram lambs may be accentuated in year-round breeding programs that can take advantage of development of early fertility. Active immunization against inhibin as a method to induce early and enhanced gametogenesis has been shown to advance puberty and to increase ovulation rate in ewe lambs [1], [2]. In ram lambs, however, Al-Obaidi et al. [1] reported that active immunization against inhibin did not advance puberty. The authors noted that observations may have been started too late to reveal differences in the first appearance of spermatozoa in ejaculates.
Different types of inhibin immunogens have been employed [3]. These include partially purified (PP) inhibin preparations derived from follicular fluid, recombinant DNA-produced inhibin α-subunit, and synthetic α-subunit peptides. Immunogens comprised of PP inhibin or a synthetic α-subunit peptide have been used successfully to advance puberty in ewe lambs [1], [2]. Synthetic α-subunit peptides afford purity, chemical consistency, and availability compared to the other types of immunogens.
The objective of the present study was to determine whether active immunization against an inhibin α-subunit peptide advances the onset of puberty in St. Croix hair sheep ram lambs in St. Croix, US Virgin Islands. At this location, most St. Croix ewes express estrus during each month of the year [4].
Section snippets
Materials and methods
St. Croix ram lambs born from November 12 to 19 were assigned alternately to control (n=8) and inhibin-immunized (n=7) treatment groups. Lambs assigned to the latter group were immunized against a synthetic peptide, α-(1–25), that matched in sequence the N-terminal 25 amino acids of the αC segment [5] of the ovine inhibin α-subunit (residues 233–257 as reported by Forage et al. [6]). The α-(1–25) peptide was coupled through a glycine–tyrosine C-terminal extension with human α-globulin (hα-G).
Results
Plasma samples collected from all ram lambs at 3 and 4 weeks of age and from control lambs throughout the study contained little if any α-(1–25)-Ab as binding of -α-(1–25) was nondetectable with few exceptions. In inhibin-immunized lambs, α-(1–25)-Ab titer was detected consistently in the plasma sample collected 1 week following the second immunization, which was administered at 7 weeks of age. Thereafter, α-(1–25)-Ab titer increased to 25 weeks and then plateaued (Fig. 1). Each boost was
Discussion
Active immunization against an inhibin α-subunit peptide conjugate did not promote early or enhanced sperm output in St. Croix ram lambs. Ram lambs were immunized against α-(1–25)-hα-G beginning at 3 weeks of age. Plasma α-(1–25)-Ab titer was detectable within 1 week following the first booster immunization administered at 7 weeks of age. Thereafter, α-(1–25)-Ab titer increased and subsequently plateaued at a level that varied among rams. Characteristics of the immune response were similar to
Acknowledgements
We thank the National Hormone and Pituitary Program, the National Institute of Diabetes and Digestive and Kidney Diseases, and Dr. A.F. Parlow for purified hormones and antisera. Appreciation is expressed to Carla Dean, Bryan Pannagl, and William Gonzales for technical assistance. The study was supported in part by the Minnesota Agricultural Experiment Station and the North Central Regional Research Project NC-111.
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