388 Effects of maternal nutrient restriction during late gestation on pre-pubertal beef calf testis size and histology

Abstract Fall-calving Hereford-SimAngus heifers [single-sired; body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] bred to a single sire were individually-fed 100% (control; CON; n = 12) or 70% (nutrient restricted; NR; n = 13) of estimated metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Post-calving, all females were fed to meet lactational nutrient requirements until weaning. From d 1 to 147 of lactation, dams were individually fed chopped tall fescue hay and supplemented in Calan gates to constrain diets of calves to milk only. After d 147, dams and calves were managed as a group in drylots, and calves could access the tall fescue hay offered to their dams. Bull calves (CON; n = 8; NR; n = 9) were castrated at 176 ± 3 (SD) d of age to represent a later pre-pubertal growth stage that is indicative of post-pubertal testis size. The epididymis and pampiniform plexus were removed, and calipers were used to determine the length and perpendicular widths of each testis. Testis weight was recorded, and testis volume was determined by water displacement in a graduated cylinder. Testis parenchyma was fixed in neutral buffered formalin for histological analyses. Seminiferous tubule diameter was measured on perpendicular diameters of 40 randomly chosen tubules with a visibly round cross-section. Data were analyzed with late gestational nutritional plane and calving date as fixed effects. Birth weight of bull calves was not affected (P > 0.99), but we previously reported that late gestational nutrient restriction decreased (P ≤ 0.04) milk production by 15% during the first 147 d of lactation. By d 63 of age, bull calves born to previously NR dams weighed less (P = 0.03) than bull calves born to CON dams. Body weight remained different (P ≤ 0.04) until castration, at which point bull calves born to previously NR dams weighed 14% less (P = 0.02) than bull calves born to CON dams. Average testis diameter was less (P = 0.03), and average testis length tended to be less (P = 0.07) for calves born to previously NR dams. Paired testes weight and volume were less (P ≤ 0.05) for calves born to previously NR dams, but testes weight relative to calf BW and average seminiferous tubule diameter were not affected (P ≥ 0.20) by late gestational nutritional plane. In the current study, pre-pubertal bull calves born to NR dams had decreased testis size, but it is difficult to delineate if this is a direct effect of gestational undernutrition on fetal development or its indirect effect on post-weaning development due to decreased milk production.