Álvaro García
The transition into lactation is a critical phase for dairy cow health, productivity, and farm profitability. This period sees the emergence of most infectious diseases and metabolic disorders, with only 56% of cows maintaining health by 60 days postpartum. These issues not only cause temporary reductions in milk production but also impact overall lactation yield, contributing to an approximate 25% culling rate within the first two months post-calving. A primary driver of these health challenges is the negative nutrient balance resulting from decreased feed intake and increased nutrient demands for fetal development and lactogenesis. This imbalance leads to decreased blood levels of minerals, amino acids, and glucose, triggering the mobilization of body fat in the form of non-esterified fatty acids (NEFA) and the accumulation of β-hydroxybutyrate, a byproduct of incomplete NEFA oxidation. These metabolic changes are associated with immune suppression and heightened susceptibility to postpartum diseases.
Importance of Prepartum Body Condition Score (BCS)
Understanding why certain cows undergo a sharp reduction in feed intake during the transition period is crucial. Previous studies have linked body condition scores above 3.75 pre-calving with more pronounced decreases in prepartum dry matter intake (DMI) compared to cows with BCS below 3.25. High BCS at dry-off is associated with reproductive disorders such as dystocia, retained fetal membranes, metritis, and endometritis. Loss of BCS during the dry period has been linked to increased incidence of uterine problems and digestive disorders, reduced milk yield, and decreased pregnancy rates following artificial insemination. Despite these links, the ideal BCS before calving that optimizes pre- and postpartum DMI and postpartum milk yield remains unclear, as does the association between prepartum BCS and energy balance (EB) before and after calving.
Recent Research Findings
A study conducted at the University of Florida (Casaro et al., 2024) involving 402 multiparous Holstein cows examined the relationship between BCS 21 days before calving and various parameters, including pre- and postpartum DMI, DMI as a percentage of body weight, EB, and milk yield.
Main findings
- Higher BCS at 21 days before calving correlated with lower DMI and EB both before and after calving, suggesting that fat cows may experience reduced appetite due to factors like reduced rumen capacity or hormonal signals like leptin.
- Milk yield increased as BCS rose from 2.5 to 3.5 but declined when BCS exceeded 3.5. Cows with BCS between 3.25 to 3.75 prepartum tended to maximize milk production.
- Fat cows consistently exhibited lower prepartum and postpartum DMI and were in a more negative EB, potentially due to ongoing inflammation triggered by excessive lipid mobilization.
- Thinner cows, while showing greater prepartum DMI and EB, tended to have lower milk yields, possibly due to insufficient reserves to support lactation and their own metabolic needs.
- Maintaining a moderate BCS around 3.25 to 3.75 before calving appears optimal for ensuring favorable outcomes in lactation performance.
Farm examples
Cow 1028 is currently 98 days into her lactation, with a body condition score (BCS) of 4.4, classifying her as fat. She initially peaked in milk production as expected, but around 70 days into lactation, her milk yield became erratic, fluctuating by 30 to 70 pounds every other day.
This erratic production, coupled with gaining condition starting at day 20 despite stable milk levels, suggests an energy intake and utilization imbalance. High BCS post-calving and continued condition gain predispose her to metabolic disorders like ketosis or fatty liver. Her inconsistent milk yield may also suggest other health issues impacting productivity. To manage her effectively, it is necessary to adjust her diet to lower energy density, monitor for metabolic disorders, and maintain a low-stress environment with veterinary oversight to optimize her health and productivity.
Cow 895 is currently at 177 days in milk and qualifies as a cow in moderate condition. She began her lactation with a BCS of 3.6, dropping to 3.2 within 10 days. She then stabilized around 3.3, with occasional drops due to lameness around 100 and 120 days in milk. Despite these challenges, she consistently exceeded production expectations, maintaining an ideal BCS. This suggests she effectively balanced her energy intake and output, even with health issues like lameness. According to Hut et al., increasing BCS from 2.5 to 3.5 predicted a 13-pound increase in daily milk yield, while increasing BCS from 3.5 to 4.5 predicted a 10-pound decrease. Similarly, a BCS increase from 2.5 to 3.5 was associated with a 322-pound increase in cumulative milk yield, whereas an increase from 3.5 to 4.5 predicted a 255-pound decrease.
Cow 896 is another multiparous cow categorized as “thin” according to the criteria of the Florida 2024 study. She calved with a BCS of 3.2 and did not lose much condition during the first month of lactation, which is typical for thin cows as they have less body fat to mobilize. However, she started to lose weight thereafter, dropping to a BCS of 2.6 by day 48 and then continued to hover around that condition. She peaked in milk production around 30 days post-calving, but her production curve has been very erratic, characterized by significant “peaks and valleys”.
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