Energy and nitrogen partitioning in dairy cows at low or high metabolizable protein levels is affected differently by postrumen glucogenic and lipogenic substrates

Abstract

This study tested the effects of energy from glucogenic (glucose; GG) or lipogenic (palm olein; LG) substrates at low (LMP) and high (HMP) metabolizable protein levels on whole-body energy and N partitioning of dairy cattle. Six rumen-fistulated, second-lactation Holstein-Friesian dairy cows (97 ± 13 d in milk) were randomly assigned to a 6 × 6 Latin square design in which each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of rest. A total mixed ration consisting of 42% corn silage, 31% grass silage, and 27% concentrate (dry matter basis) was formulated to meet 100 and 83% of net energy and metabolizable protein requirements, respectively, and was fed at 90% of ad libitum intake by individual cow. Abomasal infusion treatments were saline (LMP-C), isoenergetic infusions (digestible energy basis) of 1,319 g/d of glucose (LMP-GG), 676 g/d of palm olein (LMP-LG; major fatty acid constituents are palmitic, oleic, and linoleic acid), or 844 g/d of essential AA (HMP-C), or isoenergetic infusions of 1,319 g/d of glucose + 844 g/d of essential AA (HMP-GG) or 676 g/d of palm olein + 844 g/d of essential AA (HMP-LG). The experiment was conducted in climate respiration chambers to determine energy and N balance in conjunction with milk production and composition, nutrient digestibility, and plasma constituents. Infusion of GG and LG decreased dry matter intake, but total gross energy intake from the diet plus infusions was not affected by GG or LG. Furthermore, GG or LG did not affect total milk, protein, or lactose yields. Infusing GG or LG at the HMP level did not affect milk production differently than at the LMP level. Infusion of GG stimulated energy retention in body tissue, increased plasma glucose and insulin concentrations, decreased lipogenic metabolites in plasma, and decreased milk fat yield and milk energy output. Nitrogen intake decreased and milk N efficiency increased in response to GG, and N retention was not affected. Infusion of LG tended to increase metabolizable energy intake, increased milk fat yield and milk energy output, increased plasma triacylglycerides and long-chain fatty acid concentrations, and had no effect on energy retention. Infusion of LG decreased N intake but did not affect milk N efficiency or N retention. Compared with the LMP level, the HMP level increased dry matter intake, gross and metabolizable energy intake, and total milk, fat, protein, and lactose yields. Milk energy output increased at the HMP level, and protein level did not affect total energy retention. Heat production increased at the HMP level, but only when GG and LG were infused. The HMP level increased N intake, milk N output, and plasma urea concentration, tended to increase N retention, and decreased milk N efficiency. Regardless of protein level, GG promoted energy retention and improved milk N efficiency, but not through increased milk protein yield. Infusion of LG partitioned extra energy intake into milk and had no effect on milk N efficiency.

Mammary gland utilization of amino acids and energy metabolites differs when dairy cow rations are isoenergetically supplemented with protein and fat

“…The PT × FT interaction affecting insulin concentration, resulting in the lowest concentration when HP and HF are supplied together, aligns with the interaction on acetate concentration and suggests reduced glucose storage, a shift in energy precursor for extramammary tissues, and stimulation of lipolysis, which agrees with numerically highest glucose concentration and mammary glucose uptake, lactose yield, and fat yield on HP/HF. Arterial concentrations of NEFA and TAG increased in response to FT, in agreement with observations of others (Hammon et al, 2008;Boerman et al, 2015;Nichols et al, 2019), and with the absorption of LCFA from the digestive tract. Plasma NEFA concentrations reflect the increase in endogenous lipid flux on HF diets, possibly caused by enhanced lipolytic activity in the liver and in adipose tissue during fat feeding (Chilliard, 1993), and may have resulted from their incomplete uptake by peripheral tissues after TAG hydrolysis (Grum et al, 1996).…”

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

“…In this case, the loss of volatile N (primarily ammonia) due to the hydrolysis of urinary urea by fecal microbial urease needs to be accounted for (e.g., van Gastelen et al, 2017), whereas in the case of separate collection, urine is typically acidified (see below). Another approach to estimate urinary N excretion in respiration chambers is to measure total manure (feces + urine) N excretion as well as fecal N excretion separately and calculate urinary N loss by the difference (e.g., Nichols et al, 2019).…”

Short-Term Effect of Daily Herbage Allowance Restriction on Pasture Condition and the Performance of Grazing Dairy Cows during Autumn

“…The CP supply from high-quality pastures in the autumn usually exceeds requirements for milk production of dairy cows, whereas the energy intake is the main limiting nutrient [70]. Therefore, the use of supplementary feed is necessary to ensure a stable supply in quantity and quality of energy to avoid the energetic costs associated with excreting N through urea synthesis [71] and to optimise rumen microbial synthesis, which improves dietary N utilization (milk N in relation to N intake) [72].…”