Energy metabolism in lactating beef heifers

Area of Science:

• Animal Science
• Nutritional Physiology
• Ruminant Metabolism

Background:

• Accurate energy balance measurements are crucial for beef cow nutrition.
• Previous studies suggest breed differences in energy requirements, but data on lactating beef cows is limited.
• Understanding energy partitioning is key for optimizing feed efficiency.

Purpose of the Study:

• To determine the energy balance and requirements of lactating beef cows.
• To compare energy utilization efficiency between lactating beef heifers and dairy cows.
• To evaluate maintenance energy requirements and net energy for lactation (NE1) in beef cows.

Main Methods:

• Respiration calorimetry and digestion trials were conducted on lactating and nonlactating Hereford x Angus heifers.
• Milk yield was measured using weigh-suckle-weigh and machine milking.
• Energy balance was measured at intervals from 6 to 32 weeks postpartum.

Main Results:

• Maintenance energy requirement was 503 kJ ME/kg BW(.75), similar to lactating Holstein-Friesian cows.
• Net energy for lactation (NE1) utilization efficiency, scaled to metabolic body weight (BW(.75)), was comparable between beef heifers and dairy cows.
• Breed differences were observed in milk yield and the partitioning of metabolizable energy (ME) between milk synthesis and tissue energy retention.

Conclusions:

• Lactating beef cows exhibit similar energy utilization efficiency for milk production as dairy cows when expressed on a metabolic body weight basis.
• The primary differences between breeds appear to be in milk yield capacity and how metabolizable energy is allocated.
• These findings challenge existing standards for estimating maintenance energy requirements in beef cattle.