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Blood constituents in lactating Holstein cows influenced by hematocrit, sampling site, and diet protein and calcium
Insights
Holstein cow blood composition changes with lactation and diet. Lower protein or calcium diets and decreased hematocrit impacted nutrient levels, highlighting dietary importance.
Area of Science:
- Animal Science
- Nutritional Biochemistry
- Dairy Cattle Physiology
Background:
- Lactation significantly alters blood composition in dairy cows.
- Dietary protein and calcium levels are critical for metabolic homeostasis.
Purpose of the Study:
- To investigate the impact of dietary protein and calcium on blood constituents in lactating Holstein cows.
- To analyze arterial-venous differences in blood components at various lactation stages.
Main Methods:
- Blood samples were collected from jugular vein, internal iliac artery, and mammary vein of 24 Holstein cows.
- Cows were fed six different diets varying in protein (12-15%) and calcium (.6-.9%) content, with urea or soybean meal as protein sources.
- Measurements included hematocrit, urea nitrogen, calcium, phosphorus, magnesium, hydroxyproline, ketone bodies, and free fatty acids.
Main Results:
- Blood constituents like calcium, phosphorus, hydroxyproline, ketone bodies, magnesium, urea nitrogen, and free fatty acids varied with lactation stage and sampling site.
- Lower dietary protein (12%) or calcium (.6%) correlated with decreased urea nitrogen at a common hematocrit (36%).
- Hematocrit decreased with specific diets and lower calcium percentages, indicating increased reliance on dietary and tissue sources for blood constituents.
Conclusions:
- Dietary protein and calcium concentrations, along with their quality, are crucial for maintaining blood constituent levels during lactation.
- Understanding blood composition dynamics is essential for optimizing dairy cow nutrition and health.
- Arterial-venous sampling provides insights into tissue-specific nutrient utilization and metabolism.
Abstract:
Constituents were measured in jugular vein (days 0, 4, 14, 28, 43, 72, and 151 of lactation) and internal iliac artery and mammary vein (days 28, 72, and 151 of lactation) blood of 24 Holsteins. Six diets of grain:corn silage-urea contained percents of protein and calcium: 12, .6; 12, .9; 15, .6; 15, .9; 15, .6; 15, .9. Grain contained urea (diets 3, 4) or soybean meal (diets 5, 6). All cows were fed diet 3 the first 4 wk of lactation; then four cows were assigned to each of six diets. In jugular blood, calcium and phosphorus were lower on day 0. Hydroxyproline and ketone bodies peaked and magnesium was minimal on day 4. Hematocrit, urea nitrogen, and free fatty acids decreased with lactation. Jugular blood from younger cows had less ketone bodies, free fatty acids, and magnesium and more hematocrit, hydroxyproline, and phosphorus. Sampling site had arterial-venous differences for each constituent, with venous differences for hematocrit, free fatty acids, calcium, phosphorus, and magnesium. Hematocrit decreased with diets 1, 2, 3, 4, or .6% calcium. With a common hematocrit (36%) and change from baseline (day 28), urea nitrogen was less with 12% protein or .6% calcium. Phosphorus and magnesium decreased with 15% protein. More constituents were required from diet and tissues to maintain concentrations in blood as hematocrit decreased, indicating the importance of dietary calcium and protein concentration and quality.