Carryover effects of pre- and postweaning planes of nutrition on reproductive tract development and estrous cycle characteristics in Holstein heifers.

The objectives of this study were to investigate the carryover effects of differing pre- and postweaning planes of nutrition on prepubertal reproductive tract development and postpubertal estrous cycle characteristics in Holstein heifers. Heifer calves (n = 36) were randomly assigned to receive either a low or a high (5 or 10 L of whole milk/d, respectively) preweaning diet from 1 to 7 wk of age and either a low or a high (70 or 85% of concentrate dry total mixed ration, respectively) postweaning diet from 11 to 25 wk of age. Starting at wk 26 of age, heifers were subjected to weekly transrectal ultrasonography until wk 33 or until first ovulation to assess endometrial thickness and ovarian follicular count and size in the prepubertal phase. In a subset of heifers (n = 28), ovarian ultrasonography continued weekly until at least the second ovulation was confirmed; thereafter, ovarian dynamics (through ultrasonography) and blood progesterone (P4) were assessed every 2 d throughout 1 complete estrous cycle in the postpubertal phase. In the prepubertal phase, endometrial thickness (12.0 ± 0.4 vs. 10.8 ± 0.3 mm) and largest follicle size (11.8 ± 0.3 vs. 10.9 ± 0.2 mm) were greater in heifers fed the high postweaning diet than in those fed the low postweaning diet. Furthermore, the number of class 2 (6-9 mm) follicles was greater in heifers fed the high preweaning diet than in those fed the low preweaning diet (1.6 ± 0.1 vs. 1.1 ± 0.1), whereas the number of class 3 (>9 mm) follicles was greater in heifers fed the high postweaning diet than in those fed the low postweaning diet (1.2 ± 0.1 vs. 1.0 ± 0.1). In the postpubertal phase, overall corpus luteum and P4 dynamics did not differ among pre- or postweaning treatments; however, P4 at 4 d preceding luteolysis was lesser in heifers fed the high postweaning diet than in those fed the low postweaning diet (6.1 ± 0.4 vs. 7.7 ± 0.4 ng/mL). In addition, compared with heifers fed the low postweaning diet, those fed the high postweaning diet had a greater number of antral follicles (31.4 ± 2.2 vs. 21.4 ± 2.3) and tended to have more class 3 follicles (3.6 ± 0.3 vs. 2.7 ± 0.3). Results indicate positive carryover effects of increasing the preweaning plane of nutrition from 5 to 10 L of whole milk/d on prepubertal follicular growth in Holstein heifers. Furthermore, an increased postweaning plane of nutrition (85 vs. 70% of concentrate dry total mixed ration) advanced reproductive development through greater endometrial thickness and follicular growth in the prepubertal phase and increased the population of antral follicles in the postpubertal estrous cycle.