2026/03/17 by J.C. Anger, Christelle Loncke, Romain Bidaux +4 · 1 voice
Agricultural and Biological Sciences · Nursing · #Ruminant Nutrition and Digestive Physiology #Reproductive Physiology in Livestock #Fatty Acid Research and Health
paper · pdf · doi:10.3168/jds.2025-27544
openalex publication_date 2026/03/17 · openalex created_date 2026/03/18 · openalex updated_date 2026/07/31
Reducing the CP and MP content of diets allows for improving dairy cow nitrogen and MP efficiencies. However, when CP (≤13%-14%) and MP (<95 g/kg DM of protein digestible in the intestine) contents are reduced, DMI, milk yield, and milk component secretion generally decrease. Improving the balance of nutrient supplies (such as starch or AA) could limit these decreases in milk secretions. These effects have been tested during short-term experiments. The aim of our study was to analyze the effects of increasing the bypass starch content or better balancing AA supplies through rumen-protected AA (RP-AA: Lys, Met, and His) on lactation persistency and milk component secretions when the treatments were applied to Holstein dairy cows from 56 to 183 DIM. Forty-four dairy cows were assigned randomly to 4 groups according to a factorial arrangement of the 4 treatments (LSHDAA-: low-starch, high-degradable in the rumen without any AA supplementation; LSHDAA+: LSHD with RP-AA supplementation; HSLDAA-: high-starch, low-degradable in the rumen without RP-AA supplementation; and HSLDAA+: HSLD with RP-AA supplementation). Increasing the bypass starch content led to increases in milk yield through lactose and milk protein yield with starch × time interactions: lactation persistency improved, as did all milk component secretions in HSLD versus LSHD treatments. Increasing bypass starch slightly increased MP intake but decreased NEL intake. No changes in BCS and plasma insulin were observed when the bypass starch content was increased, probably because NEL content decreased. However, BW increased over time with a tendency to be higher with the higher bypass starch content. In addition, increasing bypass starch or RP-AA intakes increased ME efficiency (i.e., milk energy/ME). Increasing RP-AA supplies increased plasma Lys and Met concentrations, but the concentrations of plasma His only increased on LSHD. Milk protein yield as well as milk protein content and fat yield increased with RP-AA supplementation without any interaction with time. However, significant starch × AA × time interactions were observed for lactose and fat yields. These interactions mainly reflected lower lactation persistency and slopes of milk components in LSHDAA- than under the 3 other treatments. Interestingly, LSHDAA- corresponded to the lowest plasma His concentration compared with LSHDAA+, HSLDAA-, and HSLDAA+. In multiparous cows (n = 32; 8 per dietary treatment), higher mammary cell proliferation, as measured by proliferation cell nuclear antigen staining, was observed with both the HSLD versus LSHD and the AA+ (LSHDAA+ and HSLDAA+) versus AA- (LSHDAA- and HSLDAA-) diets; however, only the 2 HSLD versus LSHD diets gradually increased DMI and consequently whole nutrient supplies to sustain the higher milk persistency. Under a low-MP diet, the LSHDAA- diet proved to be a highly restrictive option for preserving lactation persistency; conversely, increasing the bypass starch content without increasing the NEL content appeared to be a promising solution to counter this negative effect on lactation persistency. Taking account of the type of nutrients (starch or AA and specifically His) absorbed in dairy feeding systems seems important when reducing the MP supply.