Effect of dietary energy composition on the energy partitioning between milk production and body fat deposition in late lactating Holstein dairy cows

Abstract

Whether adjusting the dietary energy composition can prevent the excessive obesity of dairy cows remains elusive. Therefore, this study aimed to investigate the effect of isocaloric diets with different ratios of starch and fat on energy partitioning between milk production and body fat deposition in Holstein dairy cows. Fifty-two cows (days in milk, 210.21 ± 6.95) were divided into 2 groups and fed either a high-starch diet (the ratio of net energy for lactation (NEL) supply by starch: fat was 30%:10%, HS), or a high-fat diet (the ratio of NEL supply by starch: fat was 26.67%:13.33%, HF) for 63 days. The dry matter intake (DMI) and milk yield was recorded daily. Milk samples were collected on day 1, 35 and 63 for composition analysis. The subcutaneous fat thickness was measured by Renco device and the body condition score (BCS) were evaluated on day 1 and 63. The blood biochemical indexes were also measured for the samples collected on day 1 and 63. There was no significant difference in the average DMI between the two dietary treatment groups. However, cows fed with the HS diet had higher (P < 0.05) average milk yield, and the difference enlarged with the duration of the treatments. The cows fed with the HF diet had higher milk fat percentage, serum urea nitrogen concentration, BCS, and backfat thickness (P < 0.05), but lower serum glucose concentrations (P < 0.05). Cows fed the HS diet utilized more energy for lactation (54.22% ME vs. 52.79% ME) but less energy for body fat deposition (0.56% ME vs. 1.94% ME) compared with the animals fed HF diet. Overall, these results indicated that adjusting the dietary energy composition may be an alternative approach to balance the energy partitioning between the lactation and body fat deposition in late lactating Holstein dairy cows.