Álvaro García
Research exploring the influence of dietary protein on milk production in dairy cows frequently neglects to account for body weight (BW), citing challenges in accurately measuring it over short periods. However, recent findings underscore the key role of BW in assessing residual feed intake (RFI), a crucial metric for evaluating feed efficiency. Residual feed intake quantifies how effectively animals convert feed into milk or meat, thereby impacting overall productivity and reducing operational costs. Although body reserve mobilization supports early lactation milk production, many studies overlook changes in BW and body condition score (BCS) in cows fed low-protein diets. This oversight can lead to underestimations of long-term production and income losses, despite acute dietary protein shortages triggering body protein mobilization.
Research findings
A recent study conducted at Michigan State University (Liu et al., 2021) aimed to achieve two primary objectives: (1) assess whether changes in body weight can be observed in cows fed protein-deficient diets over the short term, and (2) measure how much body weight change contributes to the overall response to a slight dietary protein deficiency. The study involved 166 lactating Holstein cows, consisting of 92 primiparous and 74 multiparous cows. Ninety-seven cows in peak lactation were initially producing 90 pounds of milk per day, while late lactation was studied in 69 cows ranging from 190 to 250 days in milk.
Peak Lactation:
- Low Protein Diet: 31% neutral detergent fiber, 32% starch, and 14% crude protein
- High Protein Diet: 29% neutral detergent fiber, 30% starch, and 18% crude protein
Both diets contained at least 9.8% rumen degradable protein on a dry matter basis.
Late Lactation:
- Low Protein Diet: 40% neutral detergent fiber, 26% starch, and 13% crude protein
- High Protein Diet: 38% neutral detergent fiber, 24% starch, and 16% crude protein
Both diets contained at least 9.0% rumen degradable protein.
Cow Performance:
Cows on the low protein diet ate less, produced less milk, and had lower body weight and empty body weight gains compared to those on the high-protein diet, during both peak and late lactation. Primiparous cows generally consumed less feed and produced less milk, although they had higher milk component concentrations during both lactation phases.
Effects of Low Protein Diet on Nutrient Digestibility:
- Peak Lactation: decreased digestibility of dry matter (62.9% vs 65.7%), of neutral detergent fiber (45.5% vs. 48.3%), and of crude protein (60.0% vs. 66.2%).
- Late Lactation: decreased digestibility of dry matter (67.8% vs. 69.8%), of neutral detergent fiber (55.8% vs. 57.6%), and of crude protein (65.7% vs. 72.9%).
Economic Analysis:
The economic analysis of feeding strategies emphasizes the critical role of considering body weight changes. Reduced body weight can lead to underestimated economic losses, as indicated by the value changes in body weight gain or loss relative to total captured revenue. Accurate body weight measurement and adjustment for protein intake are essential for dairy farmers aiming to optimize milk production and profitability. The findings of this study demonstrate that body weight changes can be detected even in the short-term and that they significantly influence milk production and economic outcomes. While impractical to manually weight cows frequently, Implementing accurate body weight measurement using 3D camera systems would be highly beneficial, overcoming traditional ensuring consistent data collection, and without stress on the animals. This approach would enhance nutritional management, herd health, cow well-being, and economic outcomes for dairy farmers.
Economic Implications of Dietary Protein Reduction:
Reducing dietary protein from 16% to 13% in late-lactation cows in this study had significant economic implications. The decrease in protein led to estimated daily losses of 2.4 Mcal of energy in milk, 2.5 Mcal of energy in body gain, 118 grams of milk protein, and 20 grams of protein in body gain, resulting in a reduction of $1.50 in milk income and $0.52 in body salvage value. These losses indicated that body tissue loss in late-lactation cows accounted for 51% of the estimated energy loss, 14% of the estimated protein loss, and 25% of the gross income loss when cows were fed a low-protein diet compared to a high-protein diet. Although feed costs decreased by $0.87 per cow due to reduced dry matter intake and lower feed costs from the decreased protein content, the overall economic impact was negative. The loss in milk income, driven by reduced milk production (55.3 pounds per day vs. 48.9 pounds per day), outweighed the savings in feed costs. Consequently, the lower protein diet led to a net economic loss, emphasizing the importance of adequate protein levels in maintaining both production and profitability in late-lactation cows.
Practical Application at the Farm Level:
Obtaining accurate cow weights was crucial in this study to monitor body condition score (BCS) and overall health, as well as calculating parameters like residual feed intake (RFI) to assess feed efficiency. Weighing also helped evaluate nutrient utilization and physiological responses to varying protein levels, providing essential data for economic analysis on milk production, feed costs, and profitability. While weekly weighing in commercial dairies is impractical, implementing daily weighing using 3D camera systems, as suggested by the study, would be highly beneficial. This approach would enable real-time monitoring of body weight changes, crucial for optimizing feed management strategies and maintaining production and profitability in dairy farming. Accurate daily monitoring can detect early changes in BCS and health, ensuring precise assessment of feed efficiency and economic impacts of dietary changes without stress on the animals, thereby enhancing herd health and farm profitability.
The negative response to dietary protein reduction in both peak and late lactation highlight the importance of body weight changes in evaluating the impact of dietary protein. This recent study’s findings indicate that body weight changes were detectable over a four-week period, underscoring that body protein mobilization or gain significantly influences milk production, especially in protein-deficient diets. By integrating comprehensive body weight monitoring and precise nutritional adjustments, dairy farmers can effectively enhance milk production, optimize feed efficiency, and maximize profitability.
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