Supplementation of rangeland primiparous Bos indicus x Bos taurus beef heifers during lactation. 2. Effects upon the reproductive development of bull calf progeny

• Published in: Theriogenology 2020-08, Vol.152, p.83-93
• Main Authors: Callaghan, M.J., Rodgers, R.J., Perry, V.E.A.
• Format: Article
• Language: English
• Subjects: Animal Feed - analysis; Animal Husbandry - methods; Animals; artificial insemination; Australia; beef cattle; blood sampling; Body Composition; body weight; Bulls; Calfhood nutrition; calves; Cattle - physiology; Dietary Proteins - administration & dosage; Dietary Proteins - pharmacology; Dietary Supplements; feeding level; Female; follicle-stimulating hormone; gonadotropin-releasing hormone; Gonandotropin; grazing; heifers; Hormones - blood; hybrids; inhibin; lactation; Lactation - physiology; luteinizing hormone; Male; natural mating; Parity; parturition; pastures; Pregnancy; progeny; protein supplements; rangelands; rearing; semen; Semen quality; Sexual Maturation - physiology; Sexual maturity; spermatozoa; Testosterone; weaning; zebu
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2020.04.032

This experiment evaluated the effect of pre-weaning plane of nutrition of dams upon reproductive development in Bos indicus x Bos taurus bull offspring reared under extensively managed conditions in the northern Australia rangelands. Following artificial insemination (AI cohort; n = 26), or natural mating (NM cohort; n = 36), grazing primiparous heifers received either nil supplement (Control; CON), thereby experiencing a moderate nutritional restriction, or were provided a protein supplement (SUPP) between parturition and weaning at mean age 199 ± (SD) 26 d. Bull progeny grazed rangeland pastures without supplementation from weaning until the experiment concluded at 675 d. At 120 ± 3 d and 140 d ± 10 d age, within the AI and NM cohort, respectively, bull calves were subjected to a GnRH challenge (1.5 μg/kg of body weight i.m.). Jugular blood samples collected immediately before and at 60 min after administration of GnRH were analysed for LH, FSH, testosterone and inhibin concentrations. Overall mean concentrations of testosterone in SUPP bulls were greater in both the AI cohort (P = 0.05) and the NM cohort (P = 0.06). At 60 d intervals during the post-weaning period, scrotal circumference (SC) was measured and semen collected to assess concentration, progressive motility and morphology of sperm. Bulls reared by SUPP heifers had greater (P = 0.05) SC at 375 d and tended to have greater (P = 0.09) mean percentage of morphologically normal sperm (PNS). Within the NM cohort, NMSUPP bulls had greater (P = 0.04) overall mean SC and tended (P = 0.07) to demonstrate both greater progressive motility and PNS. A greater incidence of sperm morphological abnormalities, associated with sexual immaturity, were observed in CON bulls. Consequently, NMCON bulls demonstrated delayed (P = 0.03) age of sexual maturity as compared to NMSUPP bulls. In summary, improving the plane of nutrition supplied to Bos indicus x Bos taurus bulls between parturition and weaning via moderate supplementation of grazing dams reduces age at sexual maturity with consequent economic advantages to the producer. •Lactational supplementation of primiparous heifers initiates increased calfhood testosterone concentrations of bull progeny.•Enhanced testicular development of bull progeny increases scrotal circumference, sperm motility and morphology.•Effects commensurate with hastened reproductive development and were manifested in early age at sexual maturity.•These findings upon measured bull traits