Milk 13C and 15N discriminations as biomarkers of feed efficiency and energy status in early lactation cows

• Published in: Animal feed science and technology 2020-11, Vol.269, p.114638, Article 114638
• Main Authors: Chen, Y.T., McNamara, J.P., Ma, G.L., Harrison, J.H., Block, E.
• Format: Article
• Language: English
• Subjects: Dairy cows; Discrimination; Early lactation; Energy balance; Feed efficiency; Stable isotope
• ISSN: 0377-8401; 1873-2216
• DOI: 10.1016/j.anifeedsci.2020.114638

•Energy balance alters milk 13C and 15N discriminations of early lactating cows.•Milk 13C and 15N discriminations highly correlate with carbon and nitrogen feed utilization efficiency for milk production.•Milk 13C and 15N discriminations indicate effects of body fat and protein mobilizations on milk component yields. Measuring feed utilization efficiency (FUE, milk production / feed intake) and energy status of dairy cows is essential to optimize dairy management and reduce feed waste, but FUE measurement is laborious and costly for dairy farms, particularly when cows are fed in groups. Our study was to investigate whether milk 13C and 15N stable isotope discriminations (naturally existing isotope; milk δ13C or δ15N – diet δ13C or δ15N) were used as biomarkers to estimate FUE, energy balance, and milk production of early lactation cows. Ten multiparous lactating cows with similar body weight (mean ± SD; 691 ± 18.0 kg) and parity (1.6 ± 0.5) were fed a homogeneous diet from 4 to 11 wk postpartum. Body fat had 1.5‰ less δ13C (P < 0.001) and muscle had similar δ13C compared to animal diet. Muscle had more than 2‰ greater δ15N than the diet (P < 0.0001). Milk 13C discrimination was reduced (P = 0.04) and milk 15N discrimination was increased (P