Effects of lactational level on reactivation of ovarian function, and interval from parturition to first visual oestrus and conception in high-producing holstein cows

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Abstract
Data were collected on 19 high-producing Holstein dairy cows from day 20post partumuntil they were either determined pregnant or reached 150 dayspost partum. Blood metabolites (progesterone (P4), glucose, beta-hydroxybutyrate (BHBA) and free fatty acids (FFA)) were related to the interval from parturition to first luteal phase, first visual oestrus and conception. Prior to data analysis, cows were divided into two groups based on their 120-day milk production and designated as below herd average (BHA; no. = 9) or above herd average (AHA; no. = 10). Average 120-day milk productions for BHA, AHA and herdmates (no. = 56) were 3932 (s.e. 157), 4841 (s.e. 60) and 4353 (s.e. 96) kg, respectively. Days from parturition to first luteal phase were not different between the BHA and AHA groups (31·7 (s.e. 1·7) and 31·5 (s.e. 6·9), respectively). In contrast, days from parturition to first visual oestrus and to conception oestrus were less for the BHA group than for the AHA group (46·8 (s.e. 4·6) and 76·9 (s.e. 7·5)v.67·7 (s.e. 5·2) and 102·5 (s.e. 9·2) days, respectively (P< 0·05)). Further, average glucose concentration from day 20 to first luteal phase was higher (P< 0·05) for the BHA group than for the AHA group (64·1 (s.e. 1·6)v.58·4 (s.e. 1·6) mg/dl). From day 20 to first visual oestrus, plasma glucose concentration increased while BHBA and FFA declined; all three metabolites then remained relatively constant until conception. These data suggest that as the amount of milk a dairy cow produces increases, the interval from parturition to first visual oestrus and conception increases. These data are consistent with a suppression of oestrus behaviour rather than with a delayed interval to ovarian cyclicity.