Biomedical subjects

G K Macleod

Publications and source records attributed to G K Macleod.

17 recordsLinked to original sources

PubMed1989

Comparative digestion in sheep and cattle fed different forage to concentrate ratios at high and low intakes.

Effect of maintenance and ad libitum intakes on digestibility of different feed fractions was studied with six ruminally fistulated cows and six ruminally fistulated wethers to validate the use of sheep as a model for cattle. Complete diets were made up of ratios of alfalfa:cracked corn and soybean meal of 80:20, 55:45, and 30:70. The regression coefficient of the line relating organic matter digestibility with proportion of concentrate in the diet was smaller for the cows at ad libitum intake than for the other groups. Increasing the intake caused a decrease in digestibility of different fractions. The depression in digestibility was greater for the 30:70 forage:concentrate diet than for the others. At high intake, digestion values in the cows were less than those in the sheep for all diets. An increase in intake depressed the digestion of cell wall fractions and cell solubles including starch in cows, whereas in sheep, an increase in intake reduced cell wall digestion and to a lesser extent cell solubles, without affecting starch digestion. The digestive physiology of these species is sufficiently different to preclude the use of sheep data in formulating nutrient requirements for cows.

Animal Feed↗

PubMed1988

Response of dairy cows in early lactation to sodium hydroxide-treated soybean meal.

To determine effects of protein and rumen degradability in rations for early lactation cows, four diets (44:56 roughage:concentrate) were formulated to contain 15 or 17.5% CP and supplemental protein from untreated or NaOH-treated soybean meal. Diets were allocated to 34 multiparous Holstein cows from d 22 to 91 of lactation. Treatment means adjusted by covariance using data from d 10 to 21 for average daily milk (kg), milk fat (%), milk protein (%), and SCM (kg) were: 15% untreated 32.9, 3.54, 3.16, and 31.3; 15% NaOH-treated 31.1, 3.59, 3.08, and 29.6; 17.5% untreated 32.2, 3.70, 3.30, and 31.2; and 17.5% NaOH-treated 32.6, 3.58, 3.17, and 30.8. Increasing dietary protein percent raised milk protein percent but not protein yield or yield of other milk components, milk yield, SCM yield, or DM intake. Protein source had no effect on production or feed intake. Decreasing dietary protein percentage and use of NaOH-treated soybean meal reduced rumen ammonia. Degradation of protein in feeds was determined in four rumen fistulated lactating cows. Sodium hydroxide treatment of soybean meal reduced protein degradation in situ.

Animal Feed↗

PubMed1984

Effect of varying protein and energy densities in complete rations fed to cows in first lactation.

Sixty-three Holstein cows in first lactation were allotted randomly at 28 days postpartum to receive one of nine rations in a 3 X 3 factorial design. Rations had crude protein 12, 15, or 18% in each of three energy densities from ratios of forage:concentrate of 75:25, 55:45, and 35:65. Corn silage and hay crop silage were combined in a ratio of 2:1 (dry basis) in each case, and diets were offered for ad libitum intake as complete feeds for an 11-wk experimental period plus 2 wk for a digestion trial. In regression analysis as energy density increased, feed intake, milk yield, milk protein, and lactose yields increased linearly, urea nitrogen in blood plasma decreased linearly, and milk fat percent and yield decreased curvilinearly. As dietary protein increased, feed intake, fat-corrected milk, milk fat yield, and plasma urea nitrogen increased linearly, and yields of milk, solids-corrected milk, milk protein, and lactose increased curvilinearly. Actual milk yield adjusted for dry matter intake increased with greater energy density but not with higher protein concentration. Increases of energy and protein each resulted in linear increases of digestibility of dry matter, crude protein, and energy of diets. There were no interactions of energy X protein for these measurements. Cows in first lactation will increase milk production in response to increasing protein over a range of energy densities when feed intake is increased.

Animals↗

PubMed1981

Response of cows to a reduction in dietary crude protein from 17% to 13% during early lactation.

Four treatments involving 48 multiparous cows (12 per group) were compared during wk 0 to 19 postpartum. Treatments involved decreasing dietary crude protein from 17% to 13% at the 5th, 10th, or 15th wk postpartum or leaving on the 17% diet throughout. Treatment means across periods for milk yields, solids-corrected-milk, dry matter intake, crude protein intake, and milk fatty acids of chain length less than or equal to palmitoleic acid, adjusted by covariance, in orders listed were 27.4, 28.0, 29.1, 29.5 kg; 23.2, 25.1 26.4, 26.8 kg; 19.0, 19.7, 20.4, 20.6 kg; 2.65, 2.98, 3.31, 3.44 kg; 59.83, 63.72, 62.74, 64.55%. There were linear increased as duration on 17% diet increased. The effect of decreasing dietary protein percent was greatest for the change at 5 wk postpartum. Milk fat, protein, and lactose percentages were not affected by treatment. Protein disappearance from nylon bags inserted in rumen fistulated steers was more rapid on 17% than 13% crude protein rations, but ration dry matter disappearance did not differ between rations.

Animal Feed↗

PubMed1980

Nutrition of the weaned holstein calf. I. Effect of dietary protein level on rumen metabolism.

The effect of various dietary crude protein (CP) levels on rumen metabolism was studied with four Holstein calves (avg wt, 146 kg) fitted with ruminal and abomasal cannulae and fed four corn-based diets supplemented with 0, 5, 10 and 15% soybean meal (SBM). The diets contained 10.2, 12.2, 14.1 and 16.1% CP. Apparent rumen digestion of dry matter (DM), organic matter (OM) and starch averaged 43.9, 48.0 and 68.4%, respectively; none of these was affected by diet (P greater than .05). There was a linear increase in abomasal flow of ammonia nitrogen (N) (P less than .01) and residual N (P less than .05) as SBM increased in the diet. There was no effect of diet on abomasal flow of bacgerial N. Abomasal flow of nonammonia N (g/100 g DM intake) increased in a linear manner (P less than .05) from 1.75 at 10.2% CP to 2.07 at 16.1% CP. When protein was greater than 12% of the diet, there was evidence of wastage of protein in the rumen. Bacterial synthesis in the rumen averaged 2.0 g/100 g organic matter apparently digested. There was no apparent effect of rumen ammonia concentration on rate of microbial synthesis in spite of the low levels (less than 5 mg N/100 ml) observed with the low CP diets. There was a linear increase in serum urea levels before and after feeding as dietary CP increased (P less than .001). Volatile fatty acid concentration in the rumen, turnover rate of the fluid phase in the rumen and rumen volume were all unaffected by changes in dietary protein (P greater than .05).

Ammonia↗

PubMed1980

Nutrition of the weaned holstein calf. II. Effect of dietary protein level on nitrogen balance, digestibility and feed intake.

Four cracked corn-based diets supplemented with 0, 5, 10 and 15% soybean meal (SBM) were fed to weaned male Holstein calves to study effects of protein level on digestibility and nitrogen balance, in one trial, and on feed intake, in another. Twelve calves were used in each trial in a replicated 4 x 4 Latin square design. Calves were 9 to 12 weeks of age at the start of the experiment and diets ranged from 9.9 to 16.2% crude protein (CP). In trial 1; feed intake was restricted to 80 g dry matter (DM) per kilogram metabolic body weight (W-75). There was a linear change (P less than .01) in apparent DM digestibility, increasing from 71.1% with the low protein diet to 75.1% with the high protein diet. Similar significant trends were observed in digestibility of organic matter (71.2 to 75.3%), nitrogen (61.6 to 72.2%), acid detergent fiber (36.2 to 44.8%) and starch (86.3 to 89.7%). Fecal starch decreased, from 28.4 to 22.1% of DM, and fecal pH increased, from 5.21 to 5.52, as SBM was substituted for corn; both of these trends were significant (P less than .01), linear component); they were also correlated (r = .55, P less than .01). Nitrogen (N) retention increased with dietary protein level (P less than .01, linear component), from 9.0 to 10.9 to 11.9 to 13.2 g N/kg digestible organic matter intake for diets 1 through 4, respectively. The same percentage of nitrogen intake was retained on all diets, but the amount of absorbed nitrogen that was retained decreased with dietary protein level (P less than .01, linear component) from 63.0% with 9.9% CP to 51.4% with 16.2% CP. In trial 2, voluntary feed intake averaged 98.2, 110.1, 106.3 and 106.5 g DM/W-75 for diets 1 to 4, respectively, (P less than .05, quadratic component). Live weight gain increased in a linear manner (P less than .01) with increasing CP, from .77kg/day with diet 1 to 1.22 kg/day with diet 4.

Animal Nutritional Physiological Phenomena↗

PubMed1980

All silage forage programs for dairy cattle. III. Health, survival, and reproduction.

Holstein-Friesian heifer calves were fed roughage consisting of corn silage only, corn silage and haycrop silage (60:40, dry matter), or corn silage and dry hay (60:40 dry matter) from birth through completion of three lactations. Forages were fed ad libitum throughout and supplemented as required. Objectives were to determine effects of forage on survival, health, and reproduction. Of the 15 calves allotted per treatment 6, 10, and 7 completed three lactations fed corn silage, corn silage plus haycrop silage, or corn silage plus hay. At any time fewer animals survived on corn silage treatment resulting in 22 completed lactations compared to 36 and 29 lactations for those receiving haycrop silage or hay. Primary reasons for removal from experiment were enzootic pneumonia, 7; reproductive failure, 8; and mastitis, 6; and not forage treatment. Fewer animals on corn silage treatment were primarily from calfhood pneumonia. Reproduction measured by age at first calving (24.6 mo), calving interval (398 days), and services per conception (2.1) was similar across treatments. Incidence of health problems was in normal ranges and similar across treatments. Forage treatment had no effect on incidence of ketosis, left displaced abomasum, or simple indigestion.

Animal Feed↗

PubMed1976

Protein and methionine hydroxy analog for lactating cows.

A 2 X 2 factorial experiment (protein 12.5 and 15.5; methionine hydroxy analog 0 and .125% dry matter) included 144 cows for one complete lactation, distributed over seven locations. Rations were formulated to the desired protein, methionine analog, and constant amounts of fiber 17%, sulfur .225%, calcium .6%, phosphorus .4%, and salt .5%. Treatment effects were not apparent for dry matter intake, daily milk and fat-corrected milk production, conversion of energy, and body weight changes. Conversion of dietary crude protein into milk protein was 34.5% for the low and 25.8% for the high protein ration. Methionine analon (0% = 2.54; .125% = 1.90). Effect of methionine analog was most apparent at low protein as 0 analog cows produced 247 kg fat, required 2.9 services/contraception, and had 156 days open whereas cows on other treatments (.125% analog and/or high protein) produced 264 kg fat, required 1.8 to 2.2 services/conception, and had 124 to 134 days open. Methionine analog response is discussed in relation to tuminal and postruminal effects as well as the interrelation with protein and energy.

Animals↗

PubMed1975