1. Effect of dietary net energy concentration on dry matter intake and energy partition in cows in mid-lactation under heat stress
- Author
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Jun Xiao, Tianhai Yan, Xiaofei Hu, Liangrong Song, Bai Xue, Fangquan Yan, Siyan Ding, and Dengpan Bu
- Subjects
0301 basic medicine ,Heat index ,Animal feed ,Chemistry ,Net energy ,0402 animal and dairy science ,04 agricultural and veterinary sciences ,General Medicine ,040201 dairy & animal science ,Heat stress ,03 medical and health sciences ,030104 developmental biology ,Milk yield ,medicine.anatomical_structure ,Lactation ,medicine ,Composition (visual arts) ,Dry matter ,Food science ,General Agricultural and Biological Sciences - 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 NEL concentration. 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 NEL content. Strong correlations were found between dietary NEL content and: (i) DM intake; (ii) NEL intake; (iii) milk energy (El ); (iv) El /metabolizable energy intake (MEI); (v) El /NEL intake, as well as between NEL intake 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/kg0.75 when extrapolating MEI to zero.
- Published
- 2016