Effect of Dietary Potassium Percent for Lactating Dairy Cows 1,2 R. J. DENNIS, R. W. H E M K E N , and D. R. JACOBSON 3 Department of Animal Sciences
University of Kentucky Lexington 40506 ABSTRACT
Three groups of Holstein cows (four cows per group) past the peak of lactation were fed dietary potassium as percent of dry matter as follows: .45% for 20 days to all groups; .45, .55, and .66% to the respective groups for 12 wk; and .66% to all groups for 19 days. Dietary potassium had no significant effect on milk fat and solids-not-fat contents of milk, milk production, or milk and blood serum cations (potassium, sodium, magnesium, calcium). However, body weights were affected. Symptoms common in potassium deficiency were not apparent. Average daily milk production, feed intake, and b o d y weight gains for the 12 wk in kilograms were: 21.9, 15.8, and 15.7; 23.4, 16.4, and 54.5; and 22.8, 19.9, and 92.9 for the .45, .55, and .66% rations. When .66% potassium was fed to groups previously fed .45 and .55% potassium, feed intake increased by 3.6 kg and 1.3 kg but increased only .2 kg in the group previously fed .66%. INTRODUCTION
The potassium (K) requirement of monogastric animals has been investigated considerably more than the requirement of ruminant animals. Studies with ruminants have shown that for maximum performance dietary K o f . 3 to .5% is required for lambs (2, 3) and .72 to .93% is required for fattening beef cattle (1, 5, 10). The requirement of the lactating cow is
based primarily on a study in 1934 which suggested that .32% dietary K was adequate to maintain a daily milk production of 7.57 liters for two lactations in two cows (6). Estimates of the K requirement of the lactating dairy cow, based on studies with other species, have been given as .7 to .8% (8), not more than .5% (15), and as high as .8 to 1.0% (14). The objective of this experiment was to study the K requirement of the lactating cow with rations containing .45, .55, and .66% K. MATERIALS AND METHODS Rations
Ingredients and percent composition of the experimental rations are in Table 1. The rations contained .45, .55, and .66% K (dry matter basis) and, on an average, contained an estimated 17.7% crude protein and 16.4% crude fiber. Rations were fed twice daily at which time the corn silage was mixed thoroughly with the other ingredients which had been combined previously. The cows were group fed and were offered enough feed to allow a 5 to 10% refusal. Feed that was not consumed was weighed once a day. Animals and Feeding Intervals
Twelve Holstein cows past the peak of lactation were selected and randomly placed in three groups of four cows per group. The cows were fed the rations according to intervals in Table 2. Samples and Weights
Received February 28, 1975. l The investigation (75-4-1) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director. 2Data are from the Masters Thesis submitted by R. J. Dennis to the Graduate School of the University of Kentucky in partial fulfillment of the requirements for the Master of Science degree. 3Route 3, Huffman Mill Road, Lexington, KY 40505.
Blood and milk samples were taken before the adjustment period, at 4 wk intervals during the experimental period, and on the last day of the post-trial period. Cows were weighed weekly, and individual milk weights were taken at each milking (twice daily). Silage samples for dry matter determination were taken weekly, and the other ingredients were sampled at mixing for dry matter analysis. 324
TECHNICAL NOTE
325
TABLE 1. Composition of rations (as fed). % composition of ration Ingredients
.45% Ka ration
.55% K ration
.66% K ration
Beet pulp Distillers dried grains Corn silage Trace mineralized salt Dicalcium phosphate Potassium chloride
21.70 37.50 40.00 .40 .40 .00
21.46 37.50 40.00 .40 .40 .24
21.22 37.50 40.00 .40 .40 .48
apercent potassium is on dry matter basis.
Analyses
Blood serum and milk were analyzed for K, sodium (Na), calcium (Ca), and magnesium (Mg) concentrations. Potassium and sodium were determined by Flame Emission Spectrophotometry. Calcium and magnesium were analyzed by Atomic Absorption Spectrophotometry. Milk fat percent was determined by MilkoTester, and total solids were by Mojonnier. Statistics
Feed intake was not analyzed statistically because animals were group fed. Analysis of variance and analysis of covariance procedures as described by Snedeeor (12) were used to analyze differences of body weight and remaining data, respectively. In covariate procedures, the measurement of the same item in the pre-experimental period was the covariate. RESULTS AND DISCUSSION
The rations were palatable, and there was no problem with animals sorting the ingredients. Although feed consmnption (Table 3) could not he analyzed statistically, there were rele-
vant trends. The average daily dry matter intake of the .45% K treatment group decreased by 2.2 kg during the experimental period but increased by 3.6 kg in the post-trial period when the .66% K ration was fed. Average daily dry matter intake increased 4.3 kg during the experimental period with an additional increase of 1.3 kg in the post-trial period as compared with the experimental period. The average daily dry matter intake of the .66% K treatment group increased by 6.6 kg, with little change occurring after the 4th wk of the experimental period. All animals were fed the .45% K ration during the first period which may have affected these results. However, feed intake was greater on the .55 and .66% rations even though the cows were group fed. One study with lactating cows (6) indicates .32% K had no effect on appetite while another study reported lower feed intake in lactating dairy cows fed a K deficient ration (.26% K) (9). Feed intake in beef steers fed .51% K was 21% lower than in steers fed .72% K (10), and work with sheep disclosed only slight differences between rations containing. 3 and .62 % K (13). The K content of the ration had a significant
TABLE 2. Feeding intervals percent potassium (dry basis) of rations fed. Treatment group Feeding interval
.45% K
.55% K
5-day adjustment
All cows gradually switched from herd ration to .45% ration
1st period (15 days) Experimental period (12 wk) Post-trial (19 days)
.45 .45 .66
.45 .55 .66
.66% K
.45 .66 .66
Journal of Dairy Science Vol. 59, No. 2
326
DENNIS ET AL.
TABLE 3. Average daily feed intake and average daily milk production.
Interval
Ration fed
Ration fed .55% K
.45% K
.66% K
.45% K
.66% K
Avg daily milk prod.
Avg daily feed intake
(kg)
(kg dry matter/cow) First perioda Experimental period 0-4 wk 5-8 wk 9-12 wk Post-trialb
.55% K
16.8
13.2
14.0
27.2
27.6
26.3
16.6 16.2 14.6 18.2
14.8 16.8 17.5 18.8
18.0 21.0 20.6 20.8
23.7 22.0 20.0 19.2
23.3 24.2 22.7 21.2
25.0 23.1 20.2 18.5
aAll cows were fed .45% K during this 15-day period. bAll cows were fed .66% K during the 19-day post-trial period.
effect (P
University of Kentucky Lexington 40506 ABSTRACT
Three groups of Holstein cows (four cows per group) past the peak of lactation were fed dietary potassium as percent of dry matter as follows: .45% for 20 days to all groups; .45, .55, and .66% to the respective groups for 12 wk; and .66% to all groups for 19 days. Dietary potassium had no significant effect on milk fat and solids-not-fat contents of milk, milk production, or milk and blood serum cations (potassium, sodium, magnesium, calcium). However, body weights were affected. Symptoms common in potassium deficiency were not apparent. Average daily milk production, feed intake, and b o d y weight gains for the 12 wk in kilograms were: 21.9, 15.8, and 15.7; 23.4, 16.4, and 54.5; and 22.8, 19.9, and 92.9 for the .45, .55, and .66% rations. When .66% potassium was fed to groups previously fed .45 and .55% potassium, feed intake increased by 3.6 kg and 1.3 kg but increased only .2 kg in the group previously fed .66%. INTRODUCTION
The potassium (K) requirement of monogastric animals has been investigated considerably more than the requirement of ruminant animals. Studies with ruminants have shown that for maximum performance dietary K o f . 3 to .5% is required for lambs (2, 3) and .72 to .93% is required for fattening beef cattle (1, 5, 10). The requirement of the lactating cow is
based primarily on a study in 1934 which suggested that .32% dietary K was adequate to maintain a daily milk production of 7.57 liters for two lactations in two cows (6). Estimates of the K requirement of the lactating dairy cow, based on studies with other species, have been given as .7 to .8% (8), not more than .5% (15), and as high as .8 to 1.0% (14). The objective of this experiment was to study the K requirement of the lactating cow with rations containing .45, .55, and .66% K. MATERIALS AND METHODS Rations
Ingredients and percent composition of the experimental rations are in Table 1. The rations contained .45, .55, and .66% K (dry matter basis) and, on an average, contained an estimated 17.7% crude protein and 16.4% crude fiber. Rations were fed twice daily at which time the corn silage was mixed thoroughly with the other ingredients which had been combined previously. The cows were group fed and were offered enough feed to allow a 5 to 10% refusal. Feed that was not consumed was weighed once a day. Animals and Feeding Intervals
Twelve Holstein cows past the peak of lactation were selected and randomly placed in three groups of four cows per group. The cows were fed the rations according to intervals in Table 2. Samples and Weights
Received February 28, 1975. l The investigation (75-4-1) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director. 2Data are from the Masters Thesis submitted by R. J. Dennis to the Graduate School of the University of Kentucky in partial fulfillment of the requirements for the Master of Science degree. 3Route 3, Huffman Mill Road, Lexington, KY 40505.
Blood and milk samples were taken before the adjustment period, at 4 wk intervals during the experimental period, and on the last day of the post-trial period. Cows were weighed weekly, and individual milk weights were taken at each milking (twice daily). Silage samples for dry matter determination were taken weekly, and the other ingredients were sampled at mixing for dry matter analysis. 324
TECHNICAL NOTE
325
TABLE 1. Composition of rations (as fed). % composition of ration Ingredients
.45% Ka ration
.55% K ration
.66% K ration
Beet pulp Distillers dried grains Corn silage Trace mineralized salt Dicalcium phosphate Potassium chloride
21.70 37.50 40.00 .40 .40 .00
21.46 37.50 40.00 .40 .40 .24
21.22 37.50 40.00 .40 .40 .48
apercent potassium is on dry matter basis.
Analyses
Blood serum and milk were analyzed for K, sodium (Na), calcium (Ca), and magnesium (Mg) concentrations. Potassium and sodium were determined by Flame Emission Spectrophotometry. Calcium and magnesium were analyzed by Atomic Absorption Spectrophotometry. Milk fat percent was determined by MilkoTester, and total solids were by Mojonnier. Statistics
Feed intake was not analyzed statistically because animals were group fed. Analysis of variance and analysis of covariance procedures as described by Snedeeor (12) were used to analyze differences of body weight and remaining data, respectively. In covariate procedures, the measurement of the same item in the pre-experimental period was the covariate. RESULTS AND DISCUSSION
The rations were palatable, and there was no problem with animals sorting the ingredients. Although feed consmnption (Table 3) could not he analyzed statistically, there were rele-
vant trends. The average daily dry matter intake of the .45% K treatment group decreased by 2.2 kg during the experimental period but increased by 3.6 kg in the post-trial period when the .66% K ration was fed. Average daily dry matter intake increased 4.3 kg during the experimental period with an additional increase of 1.3 kg in the post-trial period as compared with the experimental period. The average daily dry matter intake of the .66% K treatment group increased by 6.6 kg, with little change occurring after the 4th wk of the experimental period. All animals were fed the .45% K ration during the first period which may have affected these results. However, feed intake was greater on the .55 and .66% rations even though the cows were group fed. One study with lactating cows (6) indicates .32% K had no effect on appetite while another study reported lower feed intake in lactating dairy cows fed a K deficient ration (.26% K) (9). Feed intake in beef steers fed .51% K was 21% lower than in steers fed .72% K (10), and work with sheep disclosed only slight differences between rations containing. 3 and .62 % K (13). The K content of the ration had a significant
TABLE 2. Feeding intervals percent potassium (dry basis) of rations fed. Treatment group Feeding interval
.45% K
.55% K
5-day adjustment
All cows gradually switched from herd ration to .45% ration
1st period (15 days) Experimental period (12 wk) Post-trial (19 days)
.45 .45 .66
.45 .55 .66
.66% K
.45 .66 .66
Journal of Dairy Science Vol. 59, No. 2
326
DENNIS ET AL.
TABLE 3. Average daily feed intake and average daily milk production.
Interval
Ration fed
Ration fed .55% K
.45% K
.66% K
.45% K
.66% K
Avg daily milk prod.
Avg daily feed intake
(kg)
(kg dry matter/cow) First perioda Experimental period 0-4 wk 5-8 wk 9-12 wk Post-trialb
.55% K
16.8
13.2
14.0
27.2
27.6
26.3
16.6 16.2 14.6 18.2
14.8 16.8 17.5 18.8
18.0 21.0 20.6 20.8
23.7 22.0 20.0 19.2
23.3 24.2 22.7 21.2
25.0 23.1 20.2 18.5
aAll cows were fed .45% K during this 15-day period. bAll cows were fed .66% K during the 19-day post-trial period.
effect (P
