Principles of energy metabolism (TV4102, Lecture 32 Notes)

Discuss the transition period

- 3 weeks prior to 3-5 weeks after calving

- Increased nutritional demand and decreased dry matter intake

- In response to negative energy balance (NEB), body fat is mobilised into the bloodstream in the form of NEFAs

- Cows are predisposed to accumulate fat (as triglycerides) within the liver when large amounts of NEFAs are released from adipose (fat) tissue

- Metabolic disorders with secondary reproductive disorders [RFM, metritis], lameness, displaced abomasum, mastitis and other infectious diseases

Discuss dried-off cows (>3 weeks away from calving)

- Ideally BCS required for calving (i.e. 5 out of 8, consider post-partum anoestrus)

Discuss transition cows

- Late pregnancy, cow has to meet her own requirements (maintenance) plus the nutrient costs associated with her rapidly growing foetus(es) and udder

- Late gestation, growth of the conceptus (foetus plus membranes) equates to ~25% of the total energy requirements of the cow

Discuss DMI and energy balance in the peri-parturient period

- 550 kg Holstein-Friesian cow in her last month of pregnancy, at least 8-10 kg DM of feed per day, with a ME density of at least 10 MJ/kg DM

- During the 2-3 week period prior to calving DMI is significantly reduced/depressed

- Feed intake after calving is depressed more in cows that were over-fat at calving, they are likely to be in a greater NEB than cows of a lower BCS and fed the same diet

List the main goals of the nutritional and environmental management during the transition period

1. To reduce ruminal disruption, cows are very vulnerable to SARA resulting from supressed appetites and sudden introduction of grain

2. To minimize macromineral deficiencies (Ca, Mg, P), often associated with excess potassium which reduces the capacity of the cow to maintain serum Ca and Mg levels

3. To minimize lipid mobilisation disorders, largely influenced by a failure to provide sufficient or effective energy sources around calving

4. To avoid immune suppression, often associated with lack of energy and protein intakes, micronutrients are also required Cu, Se, Zn, I, Vit D, Vit E

Discuss energy metabolism in the pregnant and lactating cow

- In the rumen dietary carbohydrates are converted to volatile fatty acids (VFAs)

- Glucose needs to be synthesised from non-sugar sources (gluconeogenesis)

- Fatty acids are derived from the diet (VFAs), or through mobilisation of acetate in adipose tissue

- Supply of glucose (i.e. as the precursor of oxalo-acetate) is critical for the effectiveness of the oxidation of fatty acids or are metabolised into ketone bodies

Discuss fatty liver

- NEFAs accumulate when the uptake by the liver exceeds their rate of oxidation in the tricarboxylic acid (TCA).Krebs cycle or exceeds their removal as ketone bodies

- Large amounts of hepatic triglyceride lead to hepatic dysfunction via fatty liver-related syndrome

Discuss assessment of cows energy status

- Body condition scoring

- Changes in body condition score

- Level of milk production

- Fat:protein ratio in the milk

- Metabolic profiling (including NEFAs, ketones and liver function)

- Ketones, beta-hydroxybutyrate (βOHB) after calving

- Non-esterified fatty acids (NEFAs) before calving

Discuss assessment of energy status in early lactation

- High fat % in early lactation suggestive of rapid mobilisation of fat reserves predisposing to Ketosis

- Low fat % (