Influence of Concentrate Allocation and Energy Balance on Postpartum Ovarian Activity in Norwegian Cattle

¹ Norwegian School of Veterinary Science, Department of Reproduction and Forensic Medicine, Norway
² University, College of Veterinary Medicine, Cornell Department of Population Medicine and Diagnostic Sciences, Section of Epidemiology, Ithaca, NY, 14853
³ Agricultural University of Norway
⁴ Department of Reproductive Biology, Faculty of Veterinary Medicine, Estonian Agricultural University, Tartu, Estonia

The effects of different levels of concentrate, milk yield, and energy balance (EB) on postpartum ovarian activity were studied in 164 lactations from 108 moderate yielding, dual-purpose cows. All cows were of the breed Norwegian Cattle. The cows were assigned to three different concentrate allocations and had free access to roughage. Cows in the high energy group were fed as suggested by Norwegian standards, whereas cows in the low energy group were supplied with approximately 40% less concentrate than recommended. Cows in the medium energy group were fed as the low energy group prepartum and as the high energy group during the first 90 d in milk (DIM). Energy balance was estimated by subtracting energy required for maintenance and lactation from energy intake. Ovarian activity was expressed in categories (early, mid and late responders) of days to first luteal response (milk progesterone concentration >5 ng/ml) and days to first regular cycle. Energy balance and milk yield throughout the first 100 DIM were compared between categories of concentrate allocation and ovarian activity using repeated measures mixed models. Decreasing level of concentrate was related to negative EB and declining milk yield. Both negative EB and high milk yield were associated with delayed postpartum ovarian activity. Concentrate allocation did not, however, alter days to first luteal response or days to first cycle. This study demonstrated that although negative EB was associated with delayed ovulation, Norwegian Cattle adapted to less energy-dense rations by reducing milk yield rather than delaying onset of ovarian activity.

Key Words: dairy cows • energy balance • progesterone • repeated measures

Submitted on May 25, 2000
Accepted on December 4, 2000

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