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.
Feedlot performance of beef heifers implanted with Synovex-H: effect of melengestrol acetate, ovariectomy or active immunization against GnRH.
The effects on anabolic steroid implantation on feedlot performance and carcass composition and quality were examined in control (CNTRL), ovariectomized (OVX) or melengestrol acetate-fed (MGA) beef heifers or heifers actively immunized against GnRH (Anti-GnRH). Heifers (n = 112) were assigned randomly to a 2 x 4 factorial experiment. The two classes were made up of heifers not implanted and those implanted with Synovex-H. The four treatments were 1) CNTRL, 2) MGA, 3) OVX and 4) Anti-GnRH. Heifers were housed in individual pens and fed a high-energy diet for the 4-mo study. Synovex-H increased final live weight (P less than .005), carcass weight (P less than .005), ADG (P less than .0001) and feed efficiency (P less than .005) but did not alter carcass quality and yield grade (P greater than .05). Synovex-H increased deposition of protein (P less than .0001) and reduced deposition of fat (P less than .0001). Oral administration of MGA had no significant effect on feedlot performance or carcass quality. For heifers not implanted, active immunization against GnRH, but not ovariectomy, depressed ADG (P less than .05) and increased fat deposition (P less than .05) while reducing protein deposition (P less than .05). These effects of active immunization were reversed by concurrent administration of Synovex-H. Feedlot performance and carcass composition of heifers were improved by administration of anabolic steroids. When heifers were housed singly, neither ovariectomy, active immunization against GnRH nor oral administration of MGA improved feedlot performance of heifers implanted with Synovex-H.
Hill country sheep production. I. The influence of age, flock, and year on some components of reproduction rate in Romney and Border Leicester × Romney ewes.
Data from 7,091 straightbred Romney and Border Leicester × Romney ewes grazed at the Whatawhata Hill Country Research Station over the period 1959 to 1967 have been used to obtain estimates of flock and age-of-ewe effects on reproduction rate and its components and of year-to-year variation. The ewes were from six groups: a Romney control (RCR) flock, a Romney flock in which ewes were mated either to Romney (RER) or to Border Leicester rams (REB), and flocks of first-cross (F1), second-cross (F2), and third-cross (F3) Border Leicester × Romney ewes mated to first-cross Border Leicester × Romney rams. The ewes' ages at lambing varied from 2 to 5 years and no selection was practised. The ratio of number of lambs weaned per ewe present at lambing increased from the RCR (0.84) to the F1 (1.07), then declined with interbreeding to the F2 (0.92) and further to the F3 (0.87) ewes. Similar changes were evident for the percentage of ewes lambing, of multiple births, and of lambs surviving to weaning. Over...