G. M. Schuenemann

Fertility aspects in yearling beef bulls grazing endophyte-infected tall fescue pastures

During a 2-year study, yearling beef bulls were used to determine the effects of grazing on endophyte-infected tall fescue on endocrine profiles, semen quality and fertilisation potential. Bulls were allotted to graze tall fescue pastures infected with Neotyphodium coenophialum (E+; n = 20 per year) or Jesup/MaxQ (Pennington Seed, Atlanta, GA, USA; NTE; n = 10 per year). Bulls were grouped by scrotal circumference (SC), bodyweight (BW), breed composites and age to graze tall fescue pastures from mid-November until the end of June (within each year). Blood samples, BW, SC and rectal temperatures (RT) were collected every 14 days. Semen was collected from bulls every 60 days by electroejaculation and evaluated for motility and morphology. The developmental competence of oocytes fertilised in vitro with semen from respective treatments was determined. Bulls grazing E+ pastures had decreased BW gain (P < 0.01), increased overall RT (P < 0.01) and decreased prolactin (P < 0.01) compared with animals grazing NTE pastures. Neither percentage of normal sperm morphology nor motility differed between bulls grazed on the two pasture types. Semen from E+ bulls demonstrated decreased cleavage rates (P = 0.02) compared with semen from NTE bulls. However, development of cleaved embryos to the eight-cell and blastocyst stages did not differ between the two groups. In conclusion, semen from bulls grazing E+ tall fescue resulted in decreased cleavage rates in vitro, which may lower reproductive performance owing to reduced fertilisation ability.

13 Strategies to increase ovulatory follicle size and reduce ovulation time in lactating dairy cows

In vitro exposure of oocytes to elevated temperatures hastened oocyte maturation; furthermore, performing IVF of heat-stressed oocytes 5 h earlier than the usual 24 h resulted in blastocyst development similar to that of non-heat-stressed controls (Edwards et al. 2005 J. Dairy Sci. 88, 4326–4333). If elevated ambient temperatures in vivo alter oocyte maturation in a similar fashion, then new strategies are needed to induce earlier release of the oocyte from the ovulatory follicle. Current objectives were to examine follicular growth after FSH administration and examine whether treatment with FSH and an exogenously induced LH surge would hasten ovulation. On Day 0 (8 to 9 days after estrus) of the experimental period, lactating Holstein cows (n = 31; 65–115 days in milk; 1–6 lactations) received an EAZI-BREED CIDR (Pfizer Animal Health, New York, NY, USA) plus 100 µg of gonadotropin-releasing hormone (GnRH, IM; Cystorelin, Merial Ltd, Iselin, NJ, USA). On Day 7, CIDRs were removed and cows were administered 500 µg cloprostenol (IM; Estrumate, Schering-Plough Animal Health, Union, NJ, USA). Concurrently, cows were randomly allocated to receive either 80 mg FSH (FSH; n = 15; Folltropin-V, Bioniche Animal Health, Belleville, ON, Canada) or 4 mL of sterile saline (SAL; n = 16). Forty-eight h later (Day 9), cows within the FSH and SAL groups were randomly subdivided to receive either a 100-µg dose of Cysterolin (GnRH) or 3000 IU of hCG (hCG, IM; Chorulon, Intervet Inc., Millsboro, DE, USA) generating 4 treatment combinations (FSH/GnRH, n = 3; FSH/hCG, n = 7; SAL/GnRH, n = 8; and SAL/hCG, n = 8). Ovarian activity was assessed by ultrasonography to evaluate growth of the ovulatory follicle. Following CIDR removal, frequent ultrasonography was utilized to confirm ovulation (disappearance of the dominant follicle). Data were analyzed using the MIXED procedure of SAS (SAS Institute, Inc., Cary, NC, USA). Five cows from the FSH group were removed from the combination treatment due to ovulation occurring before 48 h post-CIDR removal. Size of the ovulatory follicle at time of GnRH or hCG administration was not different between FSH or SAL groups (16.7 ± 0.7 v. 17.5 ± 0.6 mm, respectively). Total growth of the ovulatory follicle from CIDR removal to ovulation did not differ between FSH (3.04 ± 0.7 mm) and SAL (2.75 ± 0.7 mm)-treated cows. As calculated from time of CIDR removal, ovulation occurred earlier in FSH (63.6 ± 4.5 h) than in SAL (77.2 ± 4.4 h; P < 0.05)-treated cows. Combination of FSH/GnRH produced the earliest ovulation (74 ± 1.2 h) which was different only from FSH/hCG (78.6 ± 0.8 h; P < 0.05), but not from SAL/GnRH or SAL/hCG (77 ± 0.8 and 78 ± 0.8 h, respectively). Regardless of FSH or SAL treatment, cows treated with GnRH ovulated earlier than those treated with hCG (75.5 ± 0.7 v. 78.3 ± 0.6 h, respectively; P < 0.05). In conclusion, while FSH was unable to increase the size of the ovulatory follicle, earlier ovulation occurred when given alone or in combination with GnRH.

308 TESTICULAR DEVELOPMENT IN PREPUBERTAL JERSEY BULL CALVES IMMUNIZED AGAINST INHIBIN

Previous studies have shown that immunization against inhibin (INH) in bull calves increased subsequent sperm production (Martin et al. 1991 Biol. Reprod. 45, 73; Bame et al. 1996 Biol. Reprod. 54, 328). The objective of the current study was to evaluate the effectiveness of gonadotropin administration at initiation of inhibin immunization in bull calves on testicular morphology. The study was performed using the inhibin peptide (bovine inhibin α1–26) conjugated to keyhole limpet hemocyanin (KLH). Primary treatments administered to Jersey bull calves (initial immunization at 27 ± 5 days of age; Day 1 of the experimental period) consisted of control (KLH, 250 µg, n e 9) or immunization (INH; 500 μg INH: 250 µg KLH, n e 9) with each emulsified in 2 mL of Freunds complete adjuvant (FCA). Booster immunizations (identical preparation in FCA) occurred every 21 days with the last administration on Day 84 of the trial. Subsets of calves were randomly assigned within primary treatments (TRT) to receive saline (1 mL, n e 3/TRT), FSH (20 mg, n e 3/TRT), or GnRH (50 μg, n e 3/TRT) every 8 h (0600, 1400, and 2200 h) from Day 1 to Day 3 of the study. Blood samples were obtained daily from Days 0–14 and weekly until testes collection (Day 91) for FSH, LH, testosterone (T), and determination of antibody titers. Body weight and scrotal circumference (SC) were measured at each immunization and immediately before testes removal. The right testis was weighed and used for absolute volume calculation of cell components per testis. Tissue sections were examined using a light microscope (400×). For each cell type, absolute volume of Sertoli, Leydig, and germ cells were counted according to the point counting method. Data were analyzed using MIXED procedure of SAS (SaS Institute, Inc., Cary, NC, USA). Antibody titers were increased in INH bulls compared to KLH bulls (P < 0.05) during the experimental period. Body weight (89.8 ± 14.2 kg), SC (14.6 ± 1.3 cm), and single testicular weight (19.2 ± 6.2 g) recorded at the end of the experimental period did not differ between treatments. Neither serum concentrations of FSH, LH, and T nor population of Leydig and Sertoli cells differed between treatment groups. However, a significant immunization X hormone treatment interaction was noted for germ cell volume per testis (P < 0.008). Administration of FSH at the time of initial immunization against inhibin significantly increased germ cell population (1.22 ± 0.1 cm3) compared to INH-saline bulls (0.64 ± 0.1 cm3) with INH-GnRH bulls intermediate (0.84 ± 0.1 cm3; P < 0.05). In contrast, germ cell volume was not increased following hormone administration in KLH bulls. These results suggest that gonadotropin administration at the time of inhibin immunization increases germ cell volume in the testis without altering Sertoli and Leydig cell volume.