Abstract

Inter-relationships between nutrition, milk production and reproduction in dairy cows were investigated in dairy herds with previous high reproductive performance. Ten herds were selected as `benchmark` farms from one area of the Waikato. Pasture and supplement intakes, and milk production were monitored on a herd basis. Bulk milk samples were taken weekly from calving through to the first three weeks of mating and assayed for levels of progesterone, urea nitrogen and b-hydroxybutyrate (BOH). Pre-mating oestrus, mating (AI) and pregnancy data were recorded. All data was expressed in relation to the planned date of mating (PSM) for each farm. Significant between farm differences were detected in all the reproductive parameters but there was no effect of supplement feeding. The mean proportion of cows cycling at PSM was 65.6 ± 3.3% (range 50.5 to 81%).The mean proportion of cows pregnant to AI at PSM + 3 weeks was 51.3 ± 2.1% (range 43 to 61.5%); at PSM + 6 weeks the mean was 74.5 ± 3.3% (61 to 89.5%); at PSM + 9 weeks it was 84.7 ± 2.2% (74.9 to 91.6%) and at PSM + 12 weeks it was 91.3 ± 1.2% (85.6 to 95.4%). Bulk milk progesterone rose linearly from a mean of 0.5 ng/ml at 8 weeks before PSM to 5.0 ng/ml at PSM and to 6.0 ng/ml three weeks later. The difference between farms at PSM ranged from (2.1 to 7.1 ng/ml). While the pattern of increase in bulk milk progesterone tended to mimic the overall pattern of oestrus activity, there was no relationship in the ranking of farms for these parameters at any time. Bulk milk BOH showed no consistent pattern over the period of measurement and levels ranged between farms in any one week from 0.01 to 0.05 mM. Bulk milk urea nitrogen concentration also showed little change on average (7.25 mM) over the pre-mating and mating periods. The significant between-farm differences in these bulk milk parameters did not appear to be related to reproductive performance. Metabolic indicators measured in bulk milk samples appear of little value for predicting reproductive performance at herd level.

JF, Smith, GA Verkerk, BA Clark, BJ McKay, and DM Duganzich

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 195-198, 2001