Our working hypothesis was that a significant period of severe underfeeding of dairy heifers during early lactation would not prevent the continuation of normal length oestrous cycles following hormonal induction of oestrus and ovulation in the early postpartum period (pp; 26.0 ( 0.7 d pp). Each of 16 Friesians (F) and 15 Jerseys (J) was treated with a CIDR device for 5 days, with one injection of prostaglandin-F2a the day before device removal and another injection 1.0 mg oestradiol benzoate 24 h after removal. The feed allowances of 8 F and 7 J heifers were reduced over the following 3 oestrous cycles, to a level where live-weights and milk yields were depressed finally by up to 15% and 36%, respectively, compared to fully fed contemporaries. Ovarian ultrasonography and monitoring of concentrations of milk progesterone (mP4) during the 1st (Cyc 1) and 3rd (Cyc 3) oestrous cycles showed that 3 Fs (1 FH and 2 FL) did not respond to initial treatment, and remained anovulatory throughout. Another 3 heifers (2 FL and 1 JL) became anovulatory after an initial positive response. The size of the first dominant follicle (DF1) and concentrations of mP4 were reduced by restricted feeding, but only during Cyc 3. This study has shown that a hormonal treatment can induce oestrus and ovulation in the majority of heifers which have been calved between 20 and 30 days. Subsequent restrictions in feeding level may convert some cycling heifers into an anoestrous state, although most will continue to cycle.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 230-232, 1996
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