Effect of protein level and methionine supplementation on dairy cows during the transition period.

Discipline: nutrition; Keywords:  dry matter intake, blood markers, milk fat, immune system.

The onset of lactation markedly increases nutrient requirements of dairy cows. The concomitant reduction in feed intake around calving predisposes transition cows to a negative nutrient balance. High-yielding dairy cows may mobilize as much as 1 kg of tissue protein per day from skeletal muscle during the first 7 to 10 days of lactation to meet their amino acid requirements. Additionally, protein mobilization starts before parturition, likely to meet amino acid requirements for growth of the foetus, uterus, and udder tissue. Some amino acids have functional roles that may help the transition through the onset of lactation. Methionine is often the most limiting amino acid for milk protein synthesis, as well as a precursor of important antioxidants and a methyl donor for synthesis of choline and carnitine, both of which are involved in lipid metabolism. Blood, milk, and liver biomarkers have indicated that at least part of the effect of methionine supplementation on milk production is due to improved immune status. Whether this positive effect on performance and immunity in those studies is a direct effect of methionine or an indirect effect of increased feed intake is not clear. Even though both protein and methionine supplementation have shown positive effects during the transition period and early lactation, these two factors have not been combined experimentally as a feeding strategy during this period. Dr F Cardoso and colleagues hypothesized that greater metabolizable protein, specifically balanced for methionine, would be beneficial to support the transition to lactation. Therefore, the objective of their study was to examine the effect of three protein treatments during the close-up period through early lactation on feed intake, milk yield, and health-related variables. The study was published in the Journal of Dairy Science, Volume 104 of 2021, page 5467 to 5478. The title of their paper is: Effect of protein level and methionine supplementation on dairy cows during the transition period.

A total of 39 Holstein cows were blocked based on parity and expected calving date and randomly assigned within each block to one of three dietary treatments: low protein (14%; LP), high protein (16%; HP), or high protein plus rumen-protected methionine (HPM). The treatments were offered from about day 18 before calving to day 45 after calving. Pre- and post-calving diets were formulated for high metabolizable protein supplied from soybean meal, and HP and HPM provided a higher metabolizable protein balance than LP.

Cows fed HP and HPM had greater feed intake (DMI) of 2 kg per day pre-calving than LP, and there was a trend for greater DMI with HPM than with HP of about 1.6 kg per day. Body weight and condition score before and after calving did not differ among treatments. High protein (HP and HPM) tended to increase milk yield during the first 45 days of lactation with about 1.75 kg per day, increased milk lactose content and urea-N in milk and plasma, tended to increase blood ß-hydroxibutyrate 14 days after calving, and tended to reduce milk per DMI compared with LP. Blood concentrations of calcium at calving and of glucose, and non-esterified fatty acids before and after calving did not differ. High protein induced lower concentration of plasma IL-1 at calving and lowered blood lymphocytes 21 days after calving, suggestive of a reduced inflammatory status compared with LP. The concentrations of IL-10, tumor necrosis factor alpha, and other haemogram variables did not differ among treatments. Addition of rumen-protected methionine to the HP diet did not alter milk yield but increased fat and total solids concentrations. The rumen-protected methionine had no effect on blood metabolites and immunity markers, with the exception of increased pre-calving insulin concentrations.

In summary: By increasing the crude protein content from 14 to 16% with high rumen undegradable protein (RUP) soybean meal during the pre-calving period increased pre-calving DMI. By feeding the HP diets also tended to decrease the concentration of IL1, suggesting reduced basal inflammatory status. In addition, cows fed the HP diets tended to have increased average daily milk yield, compared with a LP diet, as well as increased milk lactose and MUN. After calving, insulin, plasma glucose, non-esterified fatty acids (NEFA), IL10, and TNFα concentrations were not responsive to the protein supplementation levels. The inclusion of methionine in the HP diet increased the milk fat and total solids content as well as the insulin concentration before calving, but had no effect on milk yield, DMI, or the markers of health status in the blood. Taken together, the data showed the beneficial effect of increased metabolisable protein supply by the high RUP soybean meal and the HP plus methionine supplementation for dairy cows during the transition period.