title: Effect of dietary net energy concentration on dry matter intake and energy partition in cows in mid-lactation under heat stress.
abstract: This study aimed to determine the net energy requirement of Holstein cows in mid-lactation under heat stress. Twenty-five multiparous Holstein cows were randomly allocated to five groups corresponding to five isonitrogenous total mixed rations, with net energy for lactation (NEL) content of 6.15 (NE-6.15), 6.36 (NE-6.36), 6.64 (NE-6.64), 6.95 (NE-6.95), 7.36 (NE-7.36) MJ/kg of dry matter (DM), respectively. Throughout the experimental period the average temperature humidity index at 07.00, 14.00 and 22.00 hours was 72.1, 88.7, and 77.6, respectively. DM intake decreased significantly with the elevated dietary NELconcentration. Fat corrected milk increased quadratically, and milk fat content and milk energy (MJ/kg) reached the greatest in the NE-6.95 group with increasing dietary NELcontent. Strong correlations were found between dietary NELcontent and: (i) DM intake; (ii) NELintake; (iii) milk energy (El); (iv) El/metabolizable energy intake (MEI); (v) El/NELintake, as well as between NELintake and fat corrected milk yield (FCM). The suitable net energy required for dairy cows producing 1 kg FCM ranged from 5.01 to 5.03 MJ, was concluded from the above-stated regressions. Correlation between heat production (HP) and MEI could be expressed as: Log (HP) = -0.4304 + 0.2963*MEI (n = 15, R2= 0.99, Root Mean Square Error (RMSE) = 0.18). Fasting HP was 0.3712 MJ/kg0.75when extrapolating MEI to zero.
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Fangquan
authors.initials: F
authors.lastname: Yan
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China. xuebai2000@yahoo.com.
authors.forename: Bai
authors.initials: B
authors.lastname: Xue
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Liangrong
authors.initials: L
authors.lastname: Song
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiao
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Siyan
authors.initials: S
authors.lastname: Ding
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Hu
authors.affiliation: Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China.
authors.forename: Dengpan
authors.initials: D
authors.lastname: Bu
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Yaan, Sichuan, China.
authors.forename: Tianhai
authors.initials: T
authors.lastname: Yan
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology*; D000818:Animals; D002417:Cattle / Q000378:metabolism* / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D004435:Eating / Q000502:physiology*; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D005223:Fats / Q000032:analysis; D005260:Female; D018869:Heat-Shock Response / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry
chemical_list: D005223:Fats
keywords: dairy cow; energy partition; energy requirement; heat stress; performance