Milk production and nutrient partitioning as measured by ¹³C enrichment of milk components during C₃ and C₄ plant feeding in purebred Holstein and in Charolais × Holstein F₂ crossbred cows

Abstract

Nutrient partitioning was investigated in cows with different genetic merits for milk production by measuring ¹³C/¹²C ratios (reported by delta values δ¹³C) in milk components in response to C₃ (grass silage) and C₄ diets (corn silage). We hypothesised that changes of δ¹³C in milk differ between Holstein (HOL; high milk production) and Charolais × Holstein cows with medium (CHM) and low (CHL) milk production. Changes of δ¹³C (Δδ¹³C) in milk components were estimated by calculating differences of δ¹³C due to switch from C₃ to C₄ feeding. After switch to C₄ feeding, Δδ¹³C of lactose was greater in HOL than in CHL. Immediate Δδ¹³C of milk fat was the lowest in CHL. The maximal Δδ¹³C of casein was the lowest in HOL. The proportion of carbon in milk derived from diet increased with milk yield, indicating the main impact of the milk production level, but minor impact of breed, on nutrient partitioning towards the mammary gland.

Keywords:

• biochemistry
• C₃ and C₄ plant feeding
• carbon-13
• cow
• isotope ecology
• milk production
• nutrient partitioning

Acknowledgements

The authors gratefully acknowledge the staff at the Research Farm of our Institute for rearing the Holstein and F₂ cows. The authors express their gratitude to Astrid Schulz and Tanja Lenke for milk sample collection. The authors are also grateful to Kirsten Karpati, Axel Fischer, Aenne Köpnick, and Brigitte Waischnow, Institute of Nutritional Physiology, Leibniz Institute for Farm Animal Biology (FBN) for the excellent laboratory work. The authors would like to thank Dr Solvig Görs for her help in measurement of carbon isotope abundance. Hany Hillal received a scholarship from the Egyptian Government during his stay in Germany.