|Williams, K. - University Of Wisconsin|
|Weigel, K. - University Of Wisconsin|
|Esser, N. - University Of Wisconsin|
|Schlesser, H. - University Of Wisconsin|
|Hoffman, P. - Vita Plus Corporation|
|Su, H. - China Agricultural University|
|Akins, M. - University Of Wisconsin|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2019
Publication Date: 4/11/2019
Citation: Williams, K.T., Weigel, K.A., Coblentz, W.K., Esser, N.M., Schlesser, H., Hoffman, P.C., Su, H., Akins, M.S. 2019. Effect of diet energy density and genomic residual feed intake on pre-bred dairy heifer feed efficiency, growth, and manure excretion. Journal of Dairy Science. 102:4041-4050.
Interpretive Summary: Heifer rearing is a large expenditure for dairy producers. For this reason, selecting for more efficient heifers and potentially decreasing feed costs can improve profit. Residual feed intake (RFI) is the difference between an animal’s actual and expected energy intake and is a tool for selecting animals with greater feed efficiency. This study investigated the interaction between genomic RFI and diet energy density for pre-bred Holstein dairy heifers. Pre-bred heifers with different genomic RFI had similar feed efficiencies whether fed a high or low energy diet. Feeding a higher energy diet improved efficiency, but heifers gained excessive weight.
Technical Abstract: The objective of this study was to determine the growth, feed efficiency, and manure excretion of pre-bred dairy heifers with differing predicted genomic residual feed intakes (RFI) when offered diets differing with respect to energy density. Pre-bred Holstein heifers (N =128, ages 4-8 months) were blocked by weight (low, 169 ± 4.7 kg; medium-low, 205 ± 6.2 kg; medium-high, 241 ± 2.2 kg; or high, 286 ± 3.7 kg) with 32 heifers per block. Heifers in each weight block were grouped by RFI and randomly assigned to obtain 2 pens of high (HiRFI; 0.13 ± 0.073 kg DM difference from predicted intake) and 2 pens of low RFI (LoRFI; -0.069 ± 0.096 kg DM difference from predicted intake) heifers within each block (8 heifers/pen). Heifers with LoRFI were expected to have greater feed efficiency than HiRFI heifers. Dietary treatments were a high energy diet (HiE; 66.6% TDN, 14.0% CP, and 36.3% NDF, DM basis) and a low energy diet (LoE; 63.8% TDN, 13.5% CP, and 41.2% NDF, DM basis). Each pen of heifers was randomly assigned to a treatment, to obtain a 2 × 2 factorial arrangement (2 RFI levels × 2 diet energy densities). Diets were offered in a 120-d trial. Dry matter intake (DMI) was not affected by diet (7.39 vs. 7.83 kg DM/d for HiE and LoE, respectively; P = 0.14), or by RFI (7.41 vs. 7.81 kg DM/d for HiRFI and LoRFI, respectively; P = 0.17), or their interaction (P = 0.66). Average daily gain (ADG) was affected by diet, with heifers fed HiE having greater ADG than heifers fed LoE (1.14 vs. 0.97 kg/d; P < 0.01). Also, RFI affected ADG, with LoRFI heifers having greater ADG than HiRFI heifers (1.09 vs. 1.02 kg/d; P = 0.03), while the interaction of RFI and diet was not significant (P = 0.53). Feed efficiency was improved for heifers fed the HiE diet (6.44 vs. 8.02 kg DMI/kg gain for HiE and LoE, respectively; P < 0.01), but it was not affected by RFI (P = 0.48) or the interaction of RFI and diet (P = 0.62). Overall, feed efficiency of pre-bred heifers was not dependent on predicted genomic RFI, because the greater ADG of LoRFI heifers was accompanied by slightly higher DMI. Feed efficiency of heifers was reduced when heifers were fed the LoE diet, but this resulted in more optimal ADG compared to the HiE diet fed for ad-libitum intake.