“Effects of the timing of protein infusion on the daily rhythms of milk synthesis and plasma hormones and metabolites in dairy cows.” Journal of Dairy Science Vol. 106, No. 8, 2023. This article, from researchers from Penn State University, had the goal of determining the effects of intestinally absorbed protein on daily rhythms of milk and milk component synthesis and key plasma hormones and metabolites. Milk synthesis exhibits a daily rhythm that is modified by the timing of feed intake. However, it is unknown how specific nutrients entrain this daily rhythm. Amino acids have an important role in milk synthesis and may have a role in entrainment of mammary circadian rhythms.
To study this, the researchers used nine lactating Holstein cows. They were assigned to one of three treatment sequences in a 3x3 Latin square. Treatments included abomasal infusions of 500 grams per day of sodium caseinate (this protein has a high biological value for milk protein synthesis) given either continuously throughout the day (CON), for eight hours a day from 9 a.m. to 5 p.m. (DAY), or for eight hours a day from 9 p.m. to 5 a.m. (NGT). Cows were milked every six hours during the final eight days of each period.
The authors explain that lactation is regulated by many factors including circadian rhythms, which are endogenous repeating cycles of approximately 24 hours. Across several species, milk yield and composition exhibit a daily rhythm, with milk yield peaking in the morning and milkfat and protein concentrations peaking in the evening. This adaptation may have evolved to allow mammals to provide neonates with energy-dense milk at night when energy demands are greater, while simultaneously allowing the mother to forage more efficiently during the day.
Food intake can entrain circadian rhythms in metabolically important peripheral tissues such as the liver and adipose tissue. Recent research suggests mammary gland circadian rhythms can be entrained by feed intake. Still, the authors say, the specific nutrients responsible for this entrainment are unknown. They indicate that protein absorption is a compelling candidate for nutrient entrainment of the mammary circadian clock since amino acid transport, amino acid synthesis, protein synthesis and protein degradation are intimately linked with the molecular clock of several mammalian species. As such, the objective of this experiment was to examine the effects of the timing of protein absorption on the daily rhythms of milk synthesis and plasma hormone and metabolite concentrations. The authors hypothesized that altering the timing of amino acid availability in the small intestine by modifying the phase and duration of abomasally infusing sodium caseinate will shift the phasing of the daily rhythms of milk yield, milk protein concentration and yield, and plasma glucose concentration.
The study concluded that the timing of sodium caseinate infusion affected milk, milkfat and milk protein synthesis, with day infusion increasing milkfat yield and night infusion decreasing milk and milk protein yield. These changes may be due to the circadian clock of the mammary gland and coordination between milk protein synthesis and amino acid availability. Daily rhythms of milk, milkfat and milk protein yield were also affected by time of protein infusion, with day infusion having the greatest daily variation.
Future research examining the mechanism of the time of protein availability on molecular processes governing the mammary circadian clock and milkfat and protein synthesis should be conducted. Results of the current experiment suggest that altering the timing of feeding protein, specifically increasing the amount of protein fed in the morning, may have positive effects on the productivity of dairy cattle.
"Symposium review: Effects of carbohydrate digestion on feed intake and fuel supply." Journal of Dairy Science Vol. 106, No. 3, 2023. This review, from researchers from the Universities of Alberta and Michigan, describes factors affecting filling effects of forage neutral detergent fibre (NDF) and starch digestibility of grain, and discusses effects of carbohydrate digestion on feed intake and fuel supply.
The authors explain that carbohydrates are approximately 70% of diets fed to lactating dairy cows and serve as the primary source of energy. The Dairy NASEM (2021) (this is the former NRC, National Research Council) separated carbohydrates into the following four fractions based on the difference in digestibility: NDF, starch, neutral detergent soluble fibre and water-soluble carbohydrates.
Forages are more filling in the rumen than concentrates, and filling effects of forages are related to their NDF content. NDF has been used for more than 50 years as a quality parameter of forages and diets fed to dairy cows, and dietary NDF content is also used as an independent variable to predict dry matter intake (DMI) of dairy cows. However, forage NDF greatly varies in its digestion characteristics, and NDF alone, as a chemical measurement, is not sufficient to predict DMI responses of lactating dairy cows.
Regarding the filling effects of forage NDF, they are partially dependent on particle size. Another factor affecting retention of rumen digesta is its location relative to the reticulo-omasal orifice. Diets with corn silage as the primary forage had a much slower rate of passage for potential digestible NDF (pdNDF) compared with indigestible NDF (iNDF), and the authors attributed it to the difference in buoyancy. Digestible NDF is associated with fermentation gas, and it is more buoyant in the rumen and lower in specific gravity, which makes it form the fibre mat in the rumen and move away from the reticulo-omasal orifice. As such, particle size reduction does not necessarily mean its passage out of the rumen, but it is considered as a prerequisite to ruminal passage. NDF digestibility is another parameter affecting DMI, and forages with enhanced in vitro NDF digestibility can increase DMI. A meta-regression of treatment means from the literature showed a positive relationship between DMI and in vitro NDF digestibility within forage family (i.e., grass or legume). The fragility of the forage particles is another aspect of the filling effect of forage NDF. Forage fragility can be determined by measuring the electrical energy required to grind samples or the difference in the fraction of particles retained on the 1.18-millimetre sieve before and after ball milling.
Starch is another important carbohydrate, and over the last 35 years, factors affecting starch digestibility in the rumen and effects of greater starch digestion on DMI have been extensively studied. Grain type affects starch digestibility, and its ruminal degradability is in order from high to low: oats, wheat, barley, corn and milo. Conservation method (high-moisture corn versus dry ground corn) has consistent effects on DMI. Cows fed high-moisture corn had greater starch digestibility in the total tract or in the rumen, and researchers reported lower DMI for cows fed high-moisture corn. Still, this may be dependent on the level of starch of the total diet, and the reduction on DMI may occur if the diet is high in starch.
Sugar is another carbohydrate fed in the diet of lactating dairy cows, and it ferments faster than starch in general. Still, it often increases rumen pH. This is partly because sugar provides approximately 10% less carbon than starch per unit of mass due to less glycosidic bonds. In addition, sugar fermentation in the rumen increases butyrate production rather than propionate. Although sugar ferments quickly in the rumen, feeding sugar in place of starch often increased DMI of dairy cows, possibly due to preference for sweet taste or decreasing propionate flux to the liver.
The authors conclude saying that the filling effects of forage NDF are affected by in vitro NDF digestibility, fragility and forage type. Starch digestibility is affected by grain type, processing method, conservation method and endosperm type. Type of carbohydrate and its digestive characteristics can affect DMI and absorbed fuels. Previous research has increased our understanding of dietary carbohydrates, but its application for diet formulation requires integrated approaches accounting for factors affecting filling effects of forage NDF, starch digestion and temporal fuel supply.
This column brings you information regarding some of the research being done around the world and published in the Journal of Dairy Science. The objective is to bring to light areas of research that may have an immediate practical application on a dairy farm, as well as research that, even though it may not have a practical impact now, could be interesting for its future potential application. The idea is to give a brief overview of select research studies but not go into detail on each topic. Those interested in further in-depth reading can use the citations to find each study.
