Lactating overseas and NZ-derived Holstein-Friesian cows were fed either pasture or total mixed ration (NZGrass, n=14; NZ TMR, n=14; OSGrass, n=12; OS TMR, n=13). For cows ovulating before breeding began, mean postpartum anoestrous intervals (PPAI) were 39±6, 29±4, 27±6 and 23±2 d, respectively. Of 13 cows with PPAI 43d, four were NZGrass (P<0.02). Of seven with PPAI >43d, four were NZGrass (P<0.05). Growth of the first dominant follicle and corpus luteum through time, and day of emergence of the second follicle wave, measured by transrectal ultrasonography, did not differ between treatment groups. Feeding system affected mean plasma progesterone concentration at emergence of the second follicle wave and number of subordinate follicles recorded during the first follicle wave (4.5 ± 0.4 and 6.1 ± 0.5 ng/ml, P<0.02; 6.2 ± 0.6 and 4.1 ± 0.7 follicles/d, P<0.05; for grass and TMR, respectively). In summary, both genotype and feed system affected length of PPAI, while feed system influenced aspects of peripheral hormone profiles.

GA, Verkerk, S Morgan, and ES Kolver

Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 270-274, 2000
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