The transition period of the dairy cow generally refers to the last three weeks of gestation and the first three weeks of lactation. During this period, the dairy cow faces numerous physiological challenges, requiring both homeostatic and homeorhetic changes to support the demands of lactation. Management strategies to achieve a successful transition have developed over many decades. Historically, these strategies focussed on achieving high energy intakes pre-calving in an attempt to improve post-calving metabolism; however, more recent research has indicated that this approach may not be appropriate. Physiological and molecular data have indicated that imposing a slight negative energy balance (EBAL) pre-calving can improve post-calving EBAL, metabolic health indices and milk production. It was hypothesised that the challenges of the transition period would be less in a grazing system than in an intensive confinement system, due to the lower milk production and the difference in population density and, therefore, pathogen exposure. However, the molecular and immunological responses to the change of state are similar in magnitude in a moderate-yielding pasture-fed cow and in a high-yielding cow fed a total mixed ration. The collective data point to a peripartum immunosuppression, which is affected by body condition score and feeding level. This review will outline the literature and provide an assessment of the most recent transition cow management for grazing dairy cows.

Calving body condition score (BCS) is an important determinant of early-lactation dry matter intake, milk yield, and disease incidence. The current study investigated the metabolic and molecular changes induced by the change in BCS. A group of cows of mixed age and breed were managed from the second half of the previous lactation to achieve mean group BCS (10-point scale) that were high (HBCS, 5.5; n=20), medium (MBCS, 4.5; n=18), or low (LBCS, 3.5; n=19). Blood was sampled at wk -4, -3, -2, 1, 3, 5, and 6 relative to parturition to measure biomarkers of energy balance, inflammation, and liver function. Liver was biopsied on wk 1, 3, and 5 relative to parturition, and 10 cows per BCS group were used for transcript profiling via quantitative PCR. Cows in HBCS and MBCS produced more milk and had greater concentrations of nonesterified fatty acids and β-hydroxybutyrate postpartum than LBCS. Peak concentrations of nonesterified fatty acids and β-hydroxybutyrate and greater hepatic triacylglycerol concentrations were recorded in HBCS at wk 3. Consistent with blood biomarkers, HBCS and MBCS had greater expression of genes associated with fatty acid oxidation (CPT1A, ACOX1), ketogenesis (HMGCS2), and hepatokines (FGF21, ANGPTL4), whereas HBCS had the lowest expression of APOB (lipoprotein transport). Greater expression during early lactation of BBOX1 in MBCS and LBCS suggested greater de novo carnitine synthesis. The greater BCS was associated with lower expression of growth hormone/insulin-like growth factor-1 signaling axis genes (GHR1A, IGF1, and IGFALS) and greater expression of gluconeogenic genes. These likely contributed to the higher milk production and greater gluconeogenesis. Despite greater serum haptoglobin around calving, cows in HBCS and MBCS had greater blood albumin. Cows in MBCS, however, had a higher albumin:globulin ratio, probably indicating a less pronounced inflammatory status and better liver function. The marked decrease in expression of NFKB1, STAT3, HP, and SAA3 coupled with the increase in ALB on wk 3 in MBCS cows were consistent with blood measures. Overall, results suggest that the greater milk production of cows with higher calving BCS is associated with a proinflammatory response without negatively affecting expression of genes related to metabolism and the growth hormone/insulin-like growth factor-1 axis. Results highlight the sensitivity of indicators of metabolic health and inflammatory state to subtle changes in calving BCS and, collectively, indicate a suboptimal health status in cows calving at either BCS 3.5 or 5.5 relative to BCS 4.5.

The objectives of this study were to determine the effect of calving body condition score (BCS) on cow health during the transition period in a pasture-based dairying system. Feed inputs were managed during the second half of the previous lactation so that BCS differed at drying off (BCS 5.0, 4.0, and 3.0 for high, medium, and low treatments, respectively: a 10-point scale); feed allowance was managed after cows were dried off, such that the BCS differences established during lactation remained at the subsequent calving (BCS 5.5, 4.5, and 3.5; n=20, 18, and 19, for high, medium, and low treatments, respectively). After calving, cows were allocated pasture and pasture silage to ensure grazing residuals >1,600 kg of DM/ha. Milk production was measured weekly; blood was sampled regularly pre- and postpartum to measure indicators of health, and udder and uterine health were evaluated during the 6 wk after calving. Milk weight, fat, protein, and lactose yields, and fat content increased with calving BCS during the first 6 wk of lactation. The effect of calving BCS on the metabolic profile was nonlinear. Before calving, cows in the low group had lower mean plasma β-hydroxybutyrate and serum Mg concentrations and greater mean serum urea than cows in the medium and high BCS groups, which did not differ from each other. During the 6 wk after calving, cows in the low group had lower serum albumin and fructosamine concentrations than cows in the other 2 treatment groups, whereas cows in the low- and medium-BCS groups had proportionately more polymorphonucleated cells in their uterine secretions at 3 and 5 wk postpartum than high-BCS cows. In comparison, plasma β-hydroxybutyrate and nonesterified fatty acid concentrations increased linearly in early lactation with calving BCS, consistent with a greater negative energy balance in these cows. Many of the parameters measured did not vary with BCS. The results highlight that calving BCS and, therefore, BCS through early lactation are not effective indicators of functional welfare, with the analyses presented indicating that both low and high BCS at calving will increase the risk of disease: cows in the low group were more prone to reproductive compromise and fatter cows had an increased risk of metabolic diseases. These results are important in defining the welfare consequences of cow BCS.