No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Nutrition Abstracts and Reviews
The advantages and disadvantages of net energy and total digestible nutrient (TDN) methods of measuring the nutritive value of foods were discussed briefly. Several procedures for converting TDN into estimated net energy (ENE) were reported. The current objective was to determine the effect of the substitution of feed class regressions of ENE on TDN for a general regression of the combined feed classes, on the amount of error involved in converting TDN to ENE values.
Using Morrison's data on ENE and TDN, 21st edition, it appeared that all the feed classes had regression coefficients that differed significantly from the general regression coefficient for the combined classes. The feed classes, silage excepted, apparently had similar slopes for their ENE/TDN relationships and the reason why the general regression line was significantly different was because the feed classes operated at different levels of energy.
Data in Morrison's 22nd edition were treated in the same manner, and results agreed satisfactorily with the previous edition except for silage and green roughage classes. Due to the many changes between editions in TDN or ENE values, the regression lines of these two classes differed significantly from those of the earlier edition. Regression equations of the feed classes developed from data in each edition are given, along with their errors of the estimate.
In converting TDN to ENE values using Morrison's data, the appropriate feed class regression appears to be more accurate than a general regression.
Twenty Holstein cows were randomly assigned to one of five completely pelleted rations of the following Coastal Berumda- grass-concentrate ratios : Ration 1, 100:0 ; Ration 2, 75:25; Ration 3, 50:50; Ration 4, 25:75; Ration 5, 0:100, using Lucas' switchback design to study the ration effect on voluntary intake, digestibility, milk yield, and composition. Dry matter intake was significantly (P ~ .01) lower than for Ration 1. A highly significant (P ~ .01) increase in digestible energy intake of Rations 1 through 4 was observed. The associative effect of forage and concentrate on total ration digestibility increased as the percentage of concentrate was increased. The digestible energy of Rations 2, 3, and 4 was reduced approxi- mately 0.8 percentage unit below the the- oretical values for each 25% increase in concentrates of the total ration. There was a highly significant (P (.01) decrease in fat-corrected milk production from animals consuming the all-forage ra- tion and a highly significant (P (.01) linear decrease in the milk fat percentage as the concentrate was increased in the total ration. The solids-not-fat from animals consuming rations with 25% or less con- centrate were significantly (P < .01) lower than milk from animals consuming 75% or more concentrate. The percentage of protein in milk was highly significant (P (.01) among rations. Voluntary food intake is probably one of the most important factors determining total energy intake and output by ruminants. Conrad et al. (10) have shown that restrictions in feed in- take, whether they arise inherently from chem- ical and physical characteristics of the feed or from the anatomy and physiology of the cow, represent the most obvious practical limita- tions on milk production. They concluded that voluntary intake is regulated at low digestibil- ities by rumen capacity, rate of passage, and dry matter digestibility; whereas, at higher di- gestibilities, intake appears to be dependent on
Voluntary dry feed intake and dry matter digestibility were determined in 114 trials with lactating dairy cows. The rations ranged between 52 and 80% in digestibility and cow weights ranged between 625 and 1,457 lb. In a multiple regression analysis digestibility (D), fecal dry matter per 1,000 lb body weight per day (F) and body weight (W) accounted for the variation in feed intake between 52 and 66% digestibility, provided the rations were mostly roughage. R = 0.997 (P < 0.01). The terms: W0.99, D1.53, and F1.01 expressing these relationships were essentially those predicted empirically if capacity limited feed intake. With high-roughage rations between 67 and 80% dry matter digestibility, intake decreased with increasing digestibility after adjusting for body weight and productive energy. In this region, intake was directly related to the 0.73 power of the body weight at peak lactation.
It was concluded that physical and physiological factors regulating feed intake change in importance with increasing digestibility. At low digestibility they were: Body weight (reflecting roughage capacity), undigested residue per unit body weight per day (reflecting rate of passage), and dry matter digestibility. At higher digestibilities intake appeared to be dependent on metabolic size, production, and digestibility.
ResearchGate has not been able to resolve any references for this publication.