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Effect of dietary net energy concentration on dry matter intake and energy partition in cows in mid‐lactation under heat stress
Author(s) -
Yan Fangquan,
Xue Bai,
Song Liangrong,
Xiao Jun,
Ding Siyan,
Hu Xiaofei,
Bu Dengpan,
Yan Tianhai
Publication year - 2016
Publication title -
animal science journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.606
H-Index - 38
eISSN - 1740-0929
pISSN - 1344-3941
DOI - 10.1111/asj.12561
Subject(s) - lactation , dry matter , zoology , net energy , heat stress , chemistry , heat index , latin square , total mixed ration , ice calving , food science , biology , rumen , pregnancy , genetics , fermentation
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 (NE L ) 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 NE L 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 NE L content. Strong correlations were found between dietary NE L content and: (i) DM intake; (ii) NE L intake; (iii) milk energy (E l ); (iv) E l /metabolizable energy intake (MEI); (v) E l /NE L intake, as well as between NE L 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, R 2 = 0.99, Root Mean Square Error (RMSE) = 0.18). Fasting HP was 0.3712 MJ/kg 0.75 when extrapolating MEI to zero.