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Effect of residual feed intake on nutrient digestion and milk production of lactating Holstein cows fed high and low starch diets.

X. Dai

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06-24-2020

Abstract:

312
Effect of residual feed intake on nutrient digestion and milk production of lactating Holstein cows fed high and low starch diets.
X. Dai*, K. F. Kalscheur. U.S. Dairy Forage Research Center, USDA-ARS Madison, WI.

The objective of this study was to evaluate whether the difference in nutrient digestion and milk production could be explained by residual feed intake (RFI) in lactating cows. A total of 62 lactating Holstein cows (137 � 3.8 DIM) were fed either high starch (HS; 27% starch, 29% NDF) or low starch (LS; 13% starch, 37% NDF) diets. The crossover designed experiment consisted of 2 56-d treatment periods with 11-d diet adaptation. Residual feed intake (RFI) is defined as the difference between observed and expected metabolizable energy intake (MEI). High RFI cows ate more than expected and were less efficient. Cows were classified as 1 of the following: highest 10% RFI (HRFI), lowest 10% (LFRI) and medium RFI (MFRI; the remaining 80%). Greater DM and OM total-tract digestibility (P < 0.01), but lesser NDF and ADF total-tract digestibility (P < 0.01) was observed in cows fed HS diet compared with LS diet. Greater molar proportion of propionate (P < 0.01), valerate (P < 0.01) and isovalerate (P = 0.05) were found in HS-fed cows compared with LS-fed cows. Greater DMI (P < 0.01), MEI (P < 0.01), and milk yield (P < 0.01) were observed in HS-fed cows compared with LS-fed cows. Cows fed the HS diet resulted in greater milk protein concentration and lesser milk fat concentration compared with cows fed the LS diet. LRFI cows consumed 5 kg less DMI but produced 5 kg more milk compared with HRFI cows fed the HS diet. However, when cows were fed the LS diet, the LRFI cows had 6 kg less DMI and produced 5 kg less of milk compared with HRFI cows. Meanwhile, LRFI cows had more BW loss when fed the HS diet but more BW gains when fed the LS diet. Decreased total-tract digestibility and lower total VFA production resulted when LRFI cows were fed the HS diet compared with HRFI cows fed the HS diet. Our results suggest that the difference in nutrient digestion and milk production across different RFI groups are dependent on dietary starch levels. Dietary impacts need to be considered when using RFI as a feed efficiency selection tool for lactating cows.

Keywords: residual feed intake, starch, cow.

Biography: I am currently a postdoctoral researcher at the U.S. Dairy Forage Research Center at Madison-Wisconsin�since 2019. Applying omics technologies, anaerobic culture, and mathematical modeling on dairy cows, my research seeks to improve the understanding of impacts of the ruminal microbiome, host genetics, nutrient digestion, metabolic activities on the feed efficiency of dairy cows, and the associated development of analytics and selection tools to improve dairy production and efficiency.