Metabolism of fatty acids by mammary glands of cows fed normal, restricted roughage, or magnesium oxide supplemented rations

A 100-Year Review: Metabolic modifiers in dairy cattle nutrition

The first issue of the Journal of Dairy Science in 1917 opened with the text of the speech by Raymond A. Pearson, president of the Iowa State College of Agriculture, at the dedication of the new dairy building at the University of Nebraska (J. Dairy Sci. 1:4-18, 1917). Fittingly, this was the birth of a new research facility and more importantly, the beginning of a new journal devoted to the sciences of milk production and manufacture of products from milk. Metabolic modifiers of dairy cow metabolism enhance, change, or interfere with normal metabolic processes in the ruminant digestive tract or alter postabsorption partitioning of nutrients among body tissues. Papers on metabolic modifiers became more frequent in the journal around 1950. Dairy farming changed radically between 1955 and 1965. Changes in housing and feeding moved more cows outside, and cows and heifers in all stages of lactation, including the dry period, were fed as a single group. Rations became wetter with the shift to corn silage as the major forage in many rations. Liberal grain feeding met the requirements of high-producing cows and increased production per cow but introduced new challenges; for example, managing and feeding cows as a group. These changes led to the introduction of new strategies that identified and expanded the use of metabolic modifiers. Research was directed at characterizing the new problems for the dairy cow created by group feeding. Metabolic modifiers went beyond feeding the cow and included environmental and housing factors and additives to reduce the incidence and severity of many new conditions and pathologies. New collaborations began among dairy cattle specialties that broadened our understanding of the workings of the cow. The Journal of Dairy Science then and now plays an enormously important role in dissemination of the findings of dairy scientists worldwide that address existing and new technologies.

Responses in rumen fermentation and milk-fat secretion in cows receiving low-roughage diets supplemented with protected tallow

The effects on rumen fermentation and milk-fat secretion of a dietary supplement of protected tallow given to 4 Friesian cows established on a low-roughage ration and with depressed milk fat is reported. The ratios of acetate to propionate in the rumen were unaffected by the supplement and remained typical of those associated with low-roughage diets in that the proportion of propionate was increased. The supplement produced almost complete recoveries in yield and content of milk fat without any increase in intramammary fatty-acid synthesis. The recoveries were due to transfer of about 20% of the total fatty acids of the tallow supplement. These results are discussed in relation to the effects of low-roughage diets on milk-fat secretion and it is concluded that in the ‘low-fat syndrome’ the capacity of the mammary gland to absorb preformed fatty acids is not impaired.

Nutritional regulation of milk fat synthesis

Certain diets cause a marked reduction in milk fat production in ruminants. Commonly referred to as milk fat depression (MFD), the mechanism involves an interrelationship between rumen microbial processes and tissue metabolism. Numerous theories to explain this interrelationship have been proposed and investigations offer little support for theories that are based on a limitation in the supply of lipogenic precursors. Rather, the basis involves alterations in rumen biohydrogenation of dietary polyunsaturated fatty acids and a specific inhibition of mammary synthesis of milk fat. The biohydrogenation theory proposes that under certain dietary conditions, typical pathways of rumen biohydrogenation are altered to produce unique fatty acid intermediates that inhibit milk fat synthesis. Trans-10, cis-12 conjugated linoleic acid (CLA) has been identified as one example that is correlated with the reduction in milk fat. Investigations with pure isomers have shown that trans-10, cis-12 CLA is a potent inhibitor of milk fat synthesis, and similar to diet-induced MFD, the mechanism involves a coordinated reduction in mRNA abundance for key enzymes involved in the biochemical pathways of fat synthesis. A more complete identification of these naturally produced inhibitors of fat synthesis and delineation of cellular mechanisms may offer broader opportunities for application and understanding of the regulation of lipid metabolism.

Effects of Rumen-Mate on lactational performance of Holsteins fed a high grain diet

Three Latin-square trials were conducted to determine the effects of supplementing Rumen-Mate, a commercial buffer containing KCl, NaCl, and Mg and Na carbonates, on lactation performance of Holsteins. Cows were fed a basal ration of 40% corn silage and 60% concentrate in Trials 1 and 2, and 40% corn silage, 55% concentrate, and 5% alfalfa hay in Trial 3 (DM basis). In Trial 1, treatments were: basal diet, or basal diet supplemented with either 1% NaHCO3, or 1, 3, or 4.4% Rumen-Mate. Increasing dietary Rumen-Mate resulted in a linear increase in milk fat production and concentration with no difference between 1% Rumen-Mate and 1% bicarbonate. There was a significant linear decrease in milk protein concentration, but not production, with increasing concentrations of Rumen-Mate. In Trial 2 treatments were: basal diet, or basal diet supplemented with either .8% NaHCO3, 2.6% Rumen-Mate, .5% MgO, .8% NaHCO3 plus .5% MgO, or 1.8% Rumen-Mate plus .8% NaHCO3. Organic matter and CP intakes and milk protein yield and concentration were decreased by Rumen-Mate with a nonsignificant increase in milk fat concentration. Data from Trials 1 and 2 were combined with data from Trial 3, which compared basal diet, 1% bicarbonate, and 3% Rumen-Mate. The combined data showed a larger increase over basal diet in milk fat yield and concentration for 2.6 to 3% Rumen-Mate vs. .8 to 1% bicarbonate. Rumen-Mate did not decrease DM intake or protein yield relative to basal diet but did decrease protein yield 34 g/d compared with that of bicarbonate.

Effect of reactivity rate and particle size of magnesium oxide on magnesium availability, acid-base balance, mineral metabolism, and milking performance of dairy cows

Four ruminally fistulated Holstein cows were arranged in a 4 x 4 Latin-square design. Treatments consisted of a control diet and three diets containing 4% MgO (DM basis) with increasing reactivity rates (A, B, C). Diets contained corn silage and concentrate at a 40:60 ratio (DM) and were fed at 95% of ad libitum intake. Total acid-consuming capacity and solubility of MgO in vitro paralleled particle size and agreed with the solubilities in the rumen. Milk fat percentage, but not milk yield, was increased by all three MgO diets. Ruminal pH was elevated by the MgO diets across all 8 h postfeeding. MgO, reactivity A diet tended to increase ruminal acetate, total VFA production, milk yield, milk fat yield, and milk fat percentage. Effect of time postfeeding on acetate and propionate production was significant; 2 to 6 h postfeeding was the period most responsive to the diets. No significant influence on blood acid-base balance was observed. On the basis of urinary excretion of Mg, MgO sources with smaller particles are more available to cattle. Both Ca and Cl metabolism appeared to be affected by reactivity rate of MgO.

Milk production and composition in cows and goats fed alpha-ketoisocaproate

To examine whether alpha-ketoisocaproate supplementation affects milk production, 10 goats were fed either 0 or 1.1% calcium-alpha-ketoisocaproate for 2 wk and 12 cows were fed either 0 or .75% Na alpha-ketoisocaproate for 3 wk. Supplementation with alpha-ketoisocaproate increased milk fat content, milk fat yield, and 4% FCM yield in cows by an average of 5, 10, and 8%, respectively, for the treatment period. In cows, response of milk fat yield to alpha-ketoisocaproate was 120 g during wk 1 of treatment but diminished to 55 g by wk 3. Milk yield and milk protein yield tended to be greater in cows fed alpha-ketoisocaproate, but milk production efficiency and body weight were not altered by treatment in either species. Supplementation with alpha-ketoisocaproate had no significant effect on fatty acid composition of milk but tended to increase the percentage of C10 and C12 fatty acids. In goats, supplementation with alpha-ketoisocaproate had no significant effect on milk production or composition, but trends toward increased milk fat and protein content were observed. Results indicate that alpha-ketoisocaproate acutely stimulates milk fat production in lactating cows and that this effect seems to diminish with time.

Aspects of the regulation of long-chain fatty acid oxidation in bovine liver

Factors involved in regulation of bovine hepatic fatty acid oxidation were examined using liver slices. Fatty acid oxidation was measured as the conversion of 1-[14C] palmitate to 14CO2 and total [14C] acid-soluble metabolites. Extended (5 to 7 d) fasting of Holstein cows had relatively little effect on palmitate oxidation to acid-soluble metabolites by liver slices, although oxidation to CO2 was decreased. Feeding a restricted roughage, high concentrate ration to lactating cows resulted in inhibition of palmitate oxidation. Insulin, glucose, and acetate inhibited palmitate oxidation by bovine liver slices. We suggest the regulation of bovine hepatic fatty acid oxidation may be less dependent on hormonally induced alterations in enzyme activity as observed in rat liver and more dependent upon action of rumen fermentation products or their metabolites on enzyme systems involved in fatty acid oxidation.

Response of milking cows fed a high concentrate, low roughage diet plus sodium bicarbonate, magnesium oxide, or magnesium hydroxide

To determine the ability of mineral supplements to elevate depressed milk fat percent, we placed 42 Holstein cows in early to midlactation in seven blocks and assigned each to one of six treatments: control (25% corn silage and alfalfa haylage, 75% concentrate, mostly corn, dry matter); control plus magnesium oxide ground to pass a .425-mm sieve; control plus prilled magnesium oxide sieved to between 1.70 and .425 mm; control plus sodium bicarbonate; control plus reactive powdered magnesium oxide to pass a 45 microns sieve; and control plus powdered magnesium hydroxide. Sodium bicarbonate was 1% of diet as fed, magnesium oxide .5%, magnesium hydroxide .7% later reduced to .5%. Cows were fed control ration for 3 wk to induce milk fat depression, then were changed to treatment rations for 5 wk. Five cows (unblocked) were continued on each dietary treatment for a digestibility study after the feeding trial. All mineral supplements produced greater milk fat percent and yield of milk fat per day than control and all magnesium treatments produced greater milk fat percent than sodium bicarbonate. Magnesium oxide passing a .425-mm sieve produced the greatest increase of milk fat percent. Milk production was most for sodium bicarbonate treatment. Supplementation with magnesium increased ruminal magnesium concentration by factors of 1.26 to 3.75. Blood serum, urine, and fecal magnesium concentrations and fecal pH were more for cows fed magnesium than those fed sodium bicarbonate treatments. Kidney filtration ratios of element to creatinine increased for magnesium when diets were supplemented with magnesium and increased for phosphorus and sodium when diets were supplemented with sodium bicarbonate.

Neutralization of acid in the rumen by magnesium oxide and magnesium carbonate

Two reagent and two feed grade magnesium oxides and reagent grade magnesium carbonate, sodium bicarbonate, and calcium carbonate were evaluated to ascertain their ability to neutralize acid in the rumen. Rumen fluid pH was increased in vitro, compared to the control, by antacid compounds, and their increased ranked: calcium carbonate less than feed grade magnesium oxide A less than light magnesium oxide and feed grade magnesium oxide B less than heavy magnesium oxide less than magnesium carbonate less than sodium bicarbonate. Titrations at constant pH's ranging from 3.0 to 7.5 indicated that these magnesium compounds were reactive at pH's normally in the rumen although reactivity decreased with increasing pH. Intraruminal doses of feed grade magnesium oxide A and calcium carbonate did not change rumen fluid pH for other compounds ranked: feed grade magnesium oxide B less than magnesium carbonate less than heavy magnesium oxide. Feeding of heavy magnesium oxide or magnesium carbonate increased rumen fluid pH as compared to the control diet. Feeding feed grade magnesium oxide B in three quantities to cattle resulted in proportional increased in fecal pH and fluidity of feces. Two feed grade magnesium oxides differed in their ability to neutralize acid in the rumen.

Changes in plasma triglyceride fatty acids during lactation

Total blood plasma lipid and plasma triglyceride fatty acids were analyzed at an average of 33, 89, and 139 days of lactation (ranges 20 to 57, 52 to 129, and 122 to 157 days for periods I, II, and III) for 35 Holstein cows in their second or later lactation. Average milk production in the test periods was 35.7, 30.3, and 25.5 kg/day. Lipid analysis was part of a study comparing methionine hydroxy analog or sulfur for lactating cows with effects of treatment and time separated statistically. Cows fed methionine analog had a lower percent palmitate in the triglyceride fatty acid, but there was no other treatment effect. There were significant changes with time in percent total lipid and triglyceride fatty acid. Total lipid averaged 424, 526, and 529 mg/dl. Average percents of measured triglyceride fatty acid and differences with stage of lactation were: myristic, 2.96; palmitic, 27.52, I greater than II or III; palmitoleic, 2.83, I greater than II or III; stearic, 38.58 I greater than II greater than III, oleic, 20.75, I greater than II or III; and linoleic, 4.59.

Phospholipids and fat secretion by cows on normal and low fiber diets: lactational trends

Daily yields of milk, milk fat, phospholipids, and fatty acids were measured weekly during lactations of two groups of cows on a normal and restricted roughage diet. Milk yield was higher in normal cows during the initial 15 wk of lactation. Fat production decreased and was consistently lower in milk from cows on restricted roughage (from 1.2 to .4 in normal and from .8 to .3 kg/day for restricted). Phospholipid secretion decreased from an average 7 g to 3 g/day in both groups. The concentration of phospholipid in both milks fluctuated during lactation (20 to 30 mg/100 ml milk), but in milks from restricted cows it tended to increase with progress of lactation. Milk lipids from cows on restricted diets had higher phospholipid to fat ratio, (1.0 to 1.5 compared to .5 to .6 g phospholipid/100 g fat for milk from normal cows). Composition of the phospholipid classes changed slightly during lactation. Phosplatidylinositol changed most, increasing from 4 to 10 and 6 to 8% in normal and restricted milks, respectively. Fatty acids of short and medium chain lengths (C6 to C14) followed a typical quadratic regression in normal milks increasing from 10 to 30% of the total fatty acids during the first 25 wk of lactation. In restricted milk these fatty acids were already high (25%) within 2 wk and followed a linear regression with lactation. Both palmitic and stearic acid were lower in milk from restricted cows while oleic and linoleic acid were higher particularly after 10 wk of lactation.