Journal of Dairy Research (1998) 65 529â543 Printed in the United Kingdom ... *Institute of Animal Science, Agricultural Research Organization, The Volcani.
Journal of Dairy Research (1998) 65 529–543
Printed in the United Kingdom
529
Metabolic and productive responses of dairy cows to increased ion supplementation at early lactation in warm weather B NISSIM SILANIKOVE*, EPHRAIM MALTZ†, DIMITRY SHINDER*, EITAN BOGIN‡, THORKILD BASTHOLM§, NIELS J. CHRISTENSEN§ PEDER NORGGARRD§ * Institute of Animal Science, Agricultural Research Organization, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel † Institute of Agricultural Engineering, Agricultural Research Organization, The Volcani Center, PO Box 6, Bet Dagan 50250, Israel ‡ Kimaron Veterinary Institute, Bet Dagan 50 250, Israel § Department of Animal Sciences and Animal Health, The Royal Veterinary and Agricultural University, DK-1871 Frederiksberg C, Denmark (Received 18 December 1997 and accepted for publication 23 April 1998) S. We found previously that the current recommendations for Na+, K+, and Cl− contents in the diet do not meet the needs of lactating cows. The responses of cows receiving a ration with increased amounts of Na+, K+, and Cl− (E cows) were compared with those of cows consuming the same ration with a fixed concentration of these ions (C cows) between weeks 2 and 8 post partum (PP). Milk, protein, fat and lactose yields, and dry matter intake between weeks 2 and 4 PP were higher in E than in C cows. These differences did not occur between weeks 4 and 8 PP, mainly because of a higher incidence of PP complications in E cows. A greater increase in plasma insulin-like growth factor-1 concentration in E than in C animals during weeks 2 and 3 PP was consistent with the milk responses. A reduction in aldosterone concentration in E cows in weeks 2 and 3 PP was a consequence of their Na+ requirements being satisfied as a result of their enhanced Na+ intake. A subsequent elevation in aldosterone concentration in E animals was probably related to a moderate excess in K+ intake. This increase in aldosterone explains the urinary potassium loss that was detected at week 6 PP. The absence of differences between E and C cows in plasma renin activity was consistent with an absence of differences in urine volume and with the apparent utilization of the enhanced ion intake for body functions. The balance of water, Na+, K+ and Cl− in dairy cows at the onset of lactation has been studied under mild winter and hot summer Mediterranean conditions by Shalit et al. (1991) and Silanikove et al. (1997). They found that water turnover and the output of Na+, K+ and Cl− in milk and sweat increase markedly under these conditions. They also showed that at the initiation of lactation, when the increase in dry matter (DM) intake is less than that in milk yield, the current National Research Council (1989) recommendations for the content of these ions in the ration do not meet cows’ needs. The situation deteriorates during the summer, because of increased loss of these ions via sweat and saliva dribbling (Collier et al. 1982). The negative balance of Na+, K+ and Cl− was associated with a marked reduction in their loss in
530
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excreta (Shalit et al. 1991 ; Silanikove et al. 1997). The deficiency in these ions could have limited sweat secretion and hence reduced the thermoregulatory efficiency of the cows and even, perhaps, reduced their milk production (Shalit et al. 1991). The purpose of the present experiment was to test the hypothesis that the limited voluntary DM intake in early lactation imposes constraints on Na+, K+ and Cl− supply, and to investigate whether the relaxation of such constraints would improve animal performance. This hypothesis was evaluated by comparing the response of cows receiving a ration with increased amounts of Na+, K+ and Cl− with that of cows consuming the same ration with a fixed concentration of these ions. The responses compared included milk yield and composition, feed intake, water balance, kidney function, hormonal responses (aldosterone, plasma renin activity and insulin-like growth factor-1 (IGF-1)) and general blood metabolic profile. Animals A trial was conducted during the summer, between August and October 1994, in Bet Dagan, Israel. At 1–2 weeks after calving Israeli Holstein cows were assigned to control (C, n ¯ 7) and experimental (E, n ¯ 7) treatments, according to the principle of randomized blocks on the basis of precalving age, milk yield and weight. The cows were kept in ventilated individual indoor stalls, milked three times daily at 07.00, 15.00 and 22.00, and had access to a partly shaded exercise lot for 1 h. The experiment was carried out from weeks 1 to 8 post partum (PP). Two animals from the C group and three from the E group were rejected for part or all of the experiment because of illness. Treatments C cows were given a total mixed ration (TMR, Table 1) ad lib., provided once daily at 09.00. E cows were given the same TMR together with a mixture of minerals (see below) that was mixed daily with the TMR. The mineral mixture was composed of K CO , KCl, NaHCO and NaCl (3 : 1 : 1 : 1 by wt), supplying molar proportions of # $ $ 1 : 3±33 : 1±66 Na+ : K+ : Cl−. This was similar to the ratio of these ions in the TMR, which contained (g}kg) Na+ 2±3, K+10±4, Cl− 5±8 (Table 1). Each 30 g of the salt mixture provided the amounts of Na+, K+ and Cl− contained in 1 kg TMR DM, and the daily allocation was determined according to Salt mixture (g) ¯ (25®TMR offered (kg DM))¬30. Cows that produced 41 kg milk}d and consumed 22 kg DM}d of a typical Israeli ration were able to maintain a positive electrolyte balance (Silanikove et al. 1997). This ration contained electrolytes C 50 % above the National Research Council (1989) recommendations. We have chosen an intake of 25 kg DM as a reference value because this is expected to be the maximal DM intake for cows yielding 40 kg milk}d with typical high-concentrate Israeli diets (Maltz et al. 1992). The TMR allotment was 10 % above the DM intake of the previous day, but if refusals were ! 1±5 kg on a fresh weight basis, ration allotment was increased to 15 % above the DM intake of the previous day. Measurements The milk yield at each milking was automatically recorded by electronic milk meters (S. A. E. Afikim, Kibbutz Afikim 15148, Israel). Cows drank from individual drinking cups connected to electronic flow meters (precision C 1 l ; Arad Dalia Ltd,
Ion supplementation for dairy cows
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Table 1. Ingredients and chemical composition of the total mixed ration used for dairy cows in this experiment (Values are g}kg dry matter) Ingredients Wheat silage Corn silage Vetch hay Concentrates† Vitamin mix‡ Chemical composition Dry matter, g}kg as given Crude protein Neutral detergent fibre Acid detergent fibre CaCO $ Dicalcium phosphate NaCl Na+ K+ Cl− Ash
180 190 50 550 10 589 181 392 202 10±0 5±0 5±0 2±3 10±4 5±8 73±0
† Mixture of maize and soyabean meal. ‡ The vitamin–trace mineral mix contained (g}kg) vitamin A 10, vitamin D 0±00032, vitamin E 0±75, I 0±36, Fe 0±6, Mn 0±6, Cu 3±2, Co 0±08, Zn 0±6, Se 0±08.
Kibbutz Dalia 19239, Israel) and the daily water intake was measured at 10.00. Relative humidity was recorded at a nearby (0±5 km) meteorological station at the same ground level. Ambient temperature, and the rectal temperatures and breathing rates of the cows were measured daily between 08.00 and 09.00 and between 13.00 and 14.00. The following procedures were carried out once weekly. The cows were weighed, samples of milk were taken from each of the three milkings, grab samples of faeces were taken at 08.00, 15.00 and 22.00, saliva samples were taken at 13.00 by inserting a dry sponge into the mouth, and blood samples were taken from the coccygeal vein at 09.00 and 13.00. The plasma was separated and used for hormonal analysis. In addition, blood was sampled twice weekly from the coccygeal vein at 09.00 and 13.00 and the plasma was used for metabolite analysis. Nutrient digestibility and the balance of water, Na+, K+, Cl− and N were determined and kidney function was evaluated at week 7 PP on the basis of creatinine clearance as described by Silanikove et al. (1997). The procedures for measuring water intake and for quantitative collection of urine and faeces were similar to those described by Shalit et al. (1991). Assays Plasma was analysed within 24 h of collection in an autoanalyser (Kone Supra blood analyser ; Ruukintif, FIN 3200 Espoo, Finland) in the clinical laboratory of the Kimron Veterinary Institute at Bet Dagan. The following 17 constituents were determined : Na+, K+, Ca#+, Mg#+, P, urea N, creatinine, uric acid, total bilirubin, 3-hydroxybutyric acid, cholesterol, alkaline phosphatase (EC 3.1.3.1) creatine kinase (ATP : creatinine N-phosphotransferase, EC 2.7.3.2), α-amylase (EC 3.2.1.1), lactate dehydrogenase (LDH ; EC 1.1.1.27), γ-glutamyltransferase (GGT ; EC 2.3.2.2) and aspartate aminotransferase (EC 2.6.1.1). Osmolality and Cl− concentration in plasma
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were determined as described previously (Shalit et al. 1991). IGF-1 and renin were analysed with commercial radioimmunoassay kits (Incstar Corporation, Stillwater, MN 55802-0285, USA). Aldosterone was pre-extracted using a modification of the method of Roussel et al. (1983) and then analysed with a commercial radioimmunoassay kit (Coat-A-Count DPC, Los Angeles, CA 90045, USA). To 3 ml blood plasma, 21 ml dichloromethane (HPLC grade ; Sigma, Rehovot 76326, Israel) was added. The mixture was mixed vigorously in 50 ml tubes for 20 min, centrifuged at 3000 g for 10 min at room temperature, frozen for 15 min, and the dichloromethane layer decanted into a 50 ml tube. The extract was evaporated to dryness at 37 °C under flowing N gas and reconstituted with 0±3 ml (to adjust to the kit sensitivity) # of the radioimmunoassay kit matrix calibrator (aldosterone-free human plasma) for 10 min at 37 °C with periodic mixing ; a 200 µl sample of this solution was used for assay. A recovery test was carried out according to McKenzie & Clements (1974) as follows. 1,2[$H]aldosterone (Amersham International plc, Little Chalfont HP7 9NA, UK) was diluted in kit matrix calibrator to a concentration of C 200 µCi}ml and 100 µl was mixed with 2±9 ml cow plasma, incubated overnight at 37 °C in a 50 ml tube, extracted and reconstituted as described above, after which 100 µl was mixed with 3 ml liquid scintillator and counted in a β-counter. Aldosterone recovery was 91 % with a CV of 0±90. Aldosterone concentration was determined in the reconstituted plasma according to the manufacturer’s instructions. The interassay CV ranged from 4 to 6±4, intra-assay CV from 3 to 4±4, parallelism (dilution with the zero calibrator) and spiking recovery (following the addition of a known amount of aldosterone calibrator) from 97 to 100 %. Part of each of the milk samples was analysed within 48 h for protein, fat and lactose contents and somatic cell count in the Central Laboratory of the Israeli Dairy Breeders Association. The remainder of the milk samples were stored at ®17 °C, and defatted before analysis by centrifugation at 22 000 g for 10 min at room temperature. Na+, K+ and Cl− concentrations were measured by an inductively coupled plasma–atomic emission spectrometer (Spectro, Kleve, D-47533 Germany), and Ca#+, Mg#+ and P by the automatic procedure described above for plasma samples, after appropriate dilution (1 : 5 for Mg#+, 1 : 10 for Ca#+ and P). Saliva samples were centrifuged at 4000 g for 10 min at room temperature shortly after sampling, and clear samples were stored at ®17 °C. Na+, K+, Cl−, Ca#+, Mg#+ and P concentrations were determined as described for milk. Subsamples for Ca#+, Mg#+ and P analysis were centrifuged once more at 9000 g for 10 min at room temperature, and diluted 1 : 5 in the case of P. Feed, feed residuals and faeces and urine samples were prepared for analysis, and analysed for DM, organic matter, N, neutral detergent fibre, Na+, K+ and Cl− as described previously (Shalit et al. 1991). Urine was also analysed for urea and creatinine (Shalit et al. 1991). Statistical analysis Differences were tested using the GLM procedure of SAS (1982). For mineral balance and kidney function results, the model included treatment and individual cow effects. In the case of repeated measurements over time the model also included week and the interaction of week and treatment effects. Treatment effects were tested using cow within group within repetition as the error term. Only when the main effects were significant (P ! 0±05) were differences assessed, again using the GLM procedure of SAS (1982). Least square means are presented in the text and Tables.
Ion supplementation for dairy cows
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Body weight and dry matter, ion and water intakes E cows consumed on average 0±8 kg DM}d more than C cows during weeks 2–8 PP (Table 2), the differences being significant for weeks 2–4 PP (Fig. 1). There were no differences between the two groups in body weight (Table 2) or changes in body weight over time (results not shown). Na+, K+, and Cl− intakes were all higher (P ! 0±0001) in E than C cows between weeks 2 and 8 PP, but water intakes were similar (Table 2). In the E cows, Na+, K+ and Cl− intakes were more stable than in C cows throughout the experimental period : for example, compare the average values (Table 2) with the amount consumed at week 7 PP (Table 7). In the C cows, intake of a particular ion at week 1 PP was 25 % lower than at week 7 PP (Table 7), and the changes in between directly reflected the changes in feed intake. Ambient conditions, body temperature and respiration rate Relative humidity ranged from 60 to 65 % throughout the trial. Average ambient temperatures during the trial were (mean³) 26±9³0±2 °C in the morning and 29±6³0±4 °C at midday. Body temperatures did not differ between the two groups and were higher between 13.00 and 14.00 than in the morning (39±0³0±1 v. 38±5³0±1 °C, P ! 0±05). Breathing rate did not differ between the two groups and was higher between 13.00 and 14.00 than in the morning (65³6 v. 35³7}min, P ! 0±05). Milk, fat, protein and lactose yields Milk yield was on average 2±5 l}d higher (P ! 0±05) in E than in C cows (Table 3) between weeks 2 and 4 PP. Milk lactose concentration was 27 % higher (P ! 0±01) for E than for C cows between weeks 2 and 8 PP. Between weeks 2 and 4 PP, fat, protein and lactose yields were respectively 94, 86 and 187 g}d higher (P ! 0±05) for E than for C cows (Table 3). Mineral concentrations in blood plasma, saliva, faeces and milk E and C cows had similar plasma concentrations of K+, Ca#+, Mg#+ and P (Table 4). There were no differences in the concentrations of any of the individual ions in the milk from E and C cows. However, the sum of Na+, K+ and Cl− concentrations in milk were lower (P ! 0±05) for E than for C cows, Cl− being the main contributor (Table 4). E cows had a higher (P ! 0±05) Na : K ratio in their saliva. There were no differences between the two groups in ion concentrations in faeces (Table 4). Hormonal response IGF-1 concentrations increased with time, and in weeks 2 and 3 PP they were higher (P ! 0±05 and P ! 0±01 respectively) in E than in C cows (Fig. 2 a). Aldosterone concentrations increased with time in both groups, and during weeks 2 and 3 PP were lower in E than in C cows (Fig. 2 b). The average plasma renin level was 0±22 ng angiotensin}ml per h in both groups, and it did not change throughout the experiment. Enzymes and metabolites in plasma On average, none of the measured enzymes and metabolites differed between the two groups between weeks 2 and 8 PP (Table 5). The activities of LDH, GGT, aspartate aminotranferase and alkaline phosphatase, and the concentrations of total protein globulin, 3-hydroxybutyric acid, creatinine and cholesterol increased significantly with time (Table 5). The activities of LDH and GGT and the
N. S
534
Table 2. Body weights and intakes of dry matter, Na+, K+, Cl− and water in cows given increased dietary levels of electrolytes and control cows during weeks 2–8 post partum (Values are least square means with for n ¯ 7) Mineral intake, mmol}d Body weight, kg
Dry matter intake, g}d
Na+
K+
Cl−
Water intake, l}d
489 509 8 NS
16±2 15±4 0±9 NS
2625 1493 92 0±0001
6260 3988 211 0±0001
3742 2485 129 0±0002
94±7 85±6 4±4 NS
High-electrolyte Control P!
NS, not significant.
18
(a)
Dry matter intake, kg/d
17
*
*
16 15 14 13 12 11 33
(b) *
31 *
Milk yield, kg/d
29 27 25 23 21 19 1
2
3
4 5 Weeks post partum
6
7
8
Fig. 1. (a) Dry matter intake and (b) milk yield in – – –, dairy cows given increased dietary levels of electrolytes and ——, control groups of dairy cows during the first 8 weeks post partum. Values are least square means with indicated by vertical bars. Values were significantly different from those for control cows : * P ! 0±05.
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Table 3. Milk and milk fat, protein and lactose yields and concentrations for cows given increased dietary levels of electrolytes and control cows during weeks 2–4 and 2–8 post partum (Values are least square means with for n ¯ 7) Milk yield, l}d
Fat yield, g}d
Protein yield, Lactose yield, g}d g}d
Milk composition, g}kg Fat
Weeks High-electrolyte Control P!
2–4 27±6 24±5 0±6 0±05
2–8 28±6 27±9 0±7 NS
2–4 876 779 17 0±05
2–8 870 850 18 NS
2–4 772 682 14 0±05
2–8 780 765 14 NS
2–4 1330 1123 32 NS
2–8 1411 1282 33 NS
2–8 32±0 31±5 1±3 NS
Protein Lactose 2–8 28±5 27±8 0±4 NS
2–8 48±4 45±7 0±4 0±01
NS, not significant.
Table 4. Mineral concentrations in blood serum, milk, saliva and faeces for cows given increased dietary levels of electrolytes and control cows (Values are least square means with for n ¯ 7) High-electrolyte Na+ K+ Cl− Ca#+ Mg#+ P Na+ K+ Cl− Na+K+Cl− Ca#+ Mg#+ P Na+ K+ Na+ : K+ ratio Cl− Ca#+ Mg#+ P Osmolarity, mosmol}kg Na+ K+ Cl−
Control
Serum, m 137 137 43±1 43±2 100 100 2±4 2±4 0±93 0±92 2±0 1±5 Milk, m 14±9 18±1 43±1 43±2 28±5 34±1 86±6 95±5 14±2 14±3 2±8 2±9 1±2 1±1 Saliva, m 122 107 11 15 13 7 22 24 0±4 0±5 0±04 0±05 8 7 232 213 Faeces, mmol}kg dry matter 60 45 122 128 100 91
P!
0±9 0±5 0±8 0±04 0±02 0±02
NS NS NS NS NS 0±1
0±8 0±5 0±8 1±5 0±2 0±2 0±1
NS NS 0±06 0±05 NS NS NS
10 2 2 3 0±03 0±003 0±4 10
0±1 0±1 0±05 NS 0±1 0±1 NS 0±1
10 8 6
NS NS NS
NS, not significant.
concentrations of creatinine and cholesterol were higher in E than in C cows between weeks 2 and 4 PP. Digestibility and water, ion and nitrogen balance The digestibilities of DM (730 g}kg), organic matter (750 g}kg), crude protein (700 g}kg) and neutral detergent fibre (64±5 g}kg) at week 7 PP were very similar in both groups.
N. S
536 12
(a)
*
IGF-1, nmol/l
10 8 *
6 4 2 0 45
(b)
Aldosterone, pg/ml
40 35 30 25
*
20 * 15 10
1
2
3
4 5 Weeks post partum
6
7
8
Fig. 2. Serum concentrations of (a) insulin-like growth factor-1 and (b) aldosterone in – – –, dairy cows given increased dietary levels of electrolytes and ——, control groups of dairy cows during the first 8 weeks post partum. Values are least square means with indicated by vertical bars. Values were significantly different from those for control cows : * P ! 0±05.
None of the components of the water balance differed between E and C (Table 6). In both E and C cows, respiratory and cutaneous water (RCW) loss, milk water, faecal water and urine water accounted on average for 39, 26±5, 21±5 and 13 % respectively of the total water intake (C 110 kg}d). The intakes of Na+, K+ and Cl− were higher (P ! 0±001) in E than in C cows at week 7 PP (Table 7). Urine excretion was the major avenue for ion losses in both groups, and ion losses via urine were significantly higher in E than in C animals (Table 7). Ion excretion in milk was the second largest component in ion losses. There were no differences between E and C cows in the amount of milk and faecal ion output. E cows had higher retentions (P ! 0±05) of Na+, K+ and Cl− than C cows (Table 7). All the components of N balance were similar in both groups (Table 8). Output of N via urine and milk accounted for C 30 % of the intake. Protein retention was C 250 g}d in both groups.
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Ion supplementation for dairy cows
Table 5. Enzyme activities and metabolite concentrations in blood plasma, milk and faeces of cows given increased dietary levels of electrolytes and control cows (Values are least square means with for n ¯ 7) Significance of effect Highelectrolyte Enzyme activity† Lactate dehydrogenase γ-Glutamyltransferase Aspartate aminotransferase Alkaline phosphatase Protein, g}l Total protein Albumin Globulin Metabolite, mg}l 3-Hydroxybutyric acid Creatinine Urea Cholesterol Triacylglycerol
Control
Group
Time
Group¬time
91 1 2 4
NS NS NS NS
0±0001 0±003 0±0001 NS
0±05* 0±001*** NS NS
1324 22 45 61
1204 21 45 63
75 35 41
77 34 43
13 0±6 1
NS NS NS
0±0001 NS 0±0001
NS NS NS
74 10±5 240 1580 130
74 10±3 250 1410 120
6 0±2 10 80 10
NS NS NS 0±1 NS
0±05 0±0001 NS 0±0001 NS
NS 0±01** NS 0±01** NS
NS, not significant. † For methods of assay and units, see text. Values were significantly higher in high-electrolyte than in control cows : * P ! 0±05, ** P ! 0±01, *** P ! 0±001.
Table 6. Water intake, output and balance of cows given increased dietary levels of electrolytes and control cows at week 7 post partum (Values are kg}d, least square means with for n ¯ 7) High-electrolyte Control
Drinking
Food†
Total
Urinary
Faecal
Milk
Balance‡
91 86 8
22 24 1
113 110 9
16 12 3
24 24 2
29 29 2
44 45 7
† Preformed plus metabolic water. Metabolic water was calculated assuming 1 kg H O}kg dry matter # digested. ‡ Total intake®total output.
Kidney function Kidney function was assessed at week 7 PP (Table 9). There were no statistical differences between E and C cows in glomerular filtration rate or urine flow. The creatinine urine : plasma concentration ratio was lower in E than in C animals, reflecting a combination of tendencies for higher urine flows, lower urine creatinine concentrations and higher plasma creatinine concentrations in E compared with C cows (Table 9). There were no differences between the two groups in plasma and urine urea concentrations (Table 10). Urea filtration was higher (P ! 0±05) in E than in C cows but because urea reabsorption was lower (P ! 0±05) in E cows total urea excretion was similar in the two groups. This was reflected by a lower reabsorption : filtration ratio in the E cows (P ! 0±05). The higher excretion of K+ in E cows was the result of a reduction in tubular reabsorption (Table 10). This also seemed to be the case for Na+ and Cl−, but for Na+
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538
Table 7. Ion intake, output and apparent retention and balance of cows given increased dietary levels of electrolytes and control cows at week 7 post partum (Values are mequiv.}d, least square means with for n ¯ 7) Intake Na+ High-electrolyte Control P! K+ High-electrolyte Control P! Cl− High-electrolyte Control P!
Urinary
Faecal
Milk
Apparent retention†
3040 2043 75 0±001
1917 1207 140 0±01
256 196 41 NS
414 493 43 NS
453 144 95 0±05
6537 4605 150 0±001
3636 2246 250 0±01
594 612 125 NS
1256 1263 46 NS
1051 484 130 0±05
4057 2985 147 0±001
2387 1594 145 0±01
465 427 72 NS
847 972 48 NS
358 ®8 83 0±05
NS, not significant. † Apparent retention includes losses that were not measured (sweating and salivary dribbling).
Table 8. Nitrogen intake †, output and apparent retention of cows given increased dietary levels of electrolytes and control cows at week 7 post partum (Values are g}d, least square means with for n ¯ 7)
High-electrolyte Control P!
Intake
Urinary
Faecal
Milk
Apparent retention
2531 2575 105 NS
661 683 61 NS
755 769 110 NS
882 855 45 NS
233 268 95 NS
NS, not significant. † Calculated from crude protein content.
Table 9. Kidney function of cows given increased dietary levels of electrolytes and control cows at week 7 post partum (Values are least square means with for n ¯ 7)
High-electrolyte Control P!
Plasma creatinine, m
Urine creatinine, m
0±10 0±09 0±01 0±05
4±0 5±6 1±1 NS
Urine : plasma creatinine ratio 40 60 5 0±05
Glomerular filtration rate, l}d
Urine volume, l}d
583 693 39 NS
16 12 2 NS
NS, not significant.
only the urine : plasma ratio and the reabsorption : filtration ratio reached significance (P ! 0±05). The excretion of Cl− was also significantly higher (P ! 0±05) in E cows (Table 10). The reabsorption : filtration ratio for K+ became negative, indicating active secretion of the ion into the tubules. The reciprocity between the changes in urea reabsorption and concentration and in ion reabsorption and concentration
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Table 10. Plasma and kidney solute concentrations and kidney function of cows given increased dietary levels of electrolytes and control cows at week 7 post partum (Values are least square means with for n ¯ 7) Plasma Urine concn, concn, m m Urea Highelectrolyte Control P! Na+ Highelectrolyte Control P! K+ Highelectrolyte Control P! Cl− Highelectrolyte Control P! Highelectrolyte Control P!
Urine : plasma ratio
Filtration, Excretion, Reabsorption, Reabsorption : mmol}d mmol}d mmol}d filtration ratio
4±3
84
19±5
2±44
1±31
1±13
0±46
4±4 0±4 NS
110 50 NS
25±0 1±5 0±05
2±95 0±25 0±05
1±24 1±21 NS
1±71 0±15 NS
0±58 0±02 0±05
142
120
0±85
81±1
1±8
79±3
0±98
141 2 NS
107 15 NS
0±76 0±03 0±05
97±8 11±0 NS
1±2 0±2 NS
96±6 12±0 NS
0±99 0±01 NS
3±6
®1±1
®0±77
4±3
239
55±6
2±5
4±4 0±2 NS
197 21 NS
44±8 2±5 0±05
3±0 0±25 NS
106
156
1±47
61±2
105 2 NS
139 18 NS
1±32 0±03 0±05
272
1100
4±0
273 2 NS
1078 95 NS
3±9 0±02 NS
2±2 0±21 0±001 2±4
72±6 1±6 11±0 0±15 NS 0±05 Osmolality, mosmol}kg 158 17 190 21 NS
13 2 NS
0±8 0±3 0±01
0±27 0±05 0±001
58±8
0±96
71±0 9±0 NS
0±98 0±01 0±05
141
0±89
177 11 0±05
0±93 0±05 0±05
NS, not significant.
resulted in similar total urine osmolality. However, a slight diuresis in E cows was reflected by a reduction (P ! 0±05) in total osmolar reabsorption and a reduction (P ! 0±05) in osmolar reabsorption : filtration ratio (Table 10). Ion balance : physiological and nutritional implications There has been much concern in recent years about the effect of the cation–anion difference (Na+K+®Cl−) in the diet of dairy cows on their acid–base balance and, in turn, on their milk yield (West et al. 1991 ; Sanchez et al. 1994 a, b). In the present experiment, the cation–anion differences in the diets of E and C cows were similar (C30 mequiv.}kg DM), and probably did not affect the acid–base balance of the two groups. A value of 38 mequiv.}kg DM has been suggested as optimal, but a small effect on milk production in the range 25 to 50 mequiv.}kg DM has been reported (Sanchez et al. 1994 b). Thus, the cation–anion difference in the present experiment was within the range considered optimal for milk yield. Indeed, empirical calculations from the results of Schneider et al. (1986) suggest that C 60 % of the
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improvement in fat-corrected milk yield could be attributed solely to the addition of Na+ in the form of either NaCl or NaHCO . $ The addition of dietary buffers such as NaHCO , KHCO , sodium sesquicarbonate $ $ and Na CO to high-concentrate, restricted-forage diets during early lactation has # $ often been reported to improve feed intake, milk yield, milk fat and protein content (Erdman, 1988). These improvements have hitherto been related to an improvement in the buffering capacity of the rumen fluid, resulting in higher digestibility of the roughage component in the diet. However, the addition of dietary buffers in the present experiment did not affect neutral detergent fibre digestibility, suggesting that different mechanisms were responsible for the improvements in feed intake and in milk yield in E cows. The large increase in ion intake did not induce any changes in plasma ion concentrations, but it did affect ion concentrations in the secretory (saliva and milk) and excretory (urine) routes. These results are consistent with those of Belibasakis & Triantos (1991), who found no effect on various blood components of sodium carbonate supplementation during early lactation. The lower milk ion excretion in E than in C animals is more likely to be related to changes in lactose metabolism than to a direct effect of ion supplementation. In Na+-deficient ruminants, there is a replacement of Na+ with K+ in saliva, causing a reduction in the Na+ : K+ ratio (Underwood, 1981). Thus, the rise in the Na+ : K+ ratio and a trend toward a rise in salivary Na+ supports the conclusion that the C cows were Na+-deficient. In fact, the Na+ : K+ ratio in E cows was consistent with the Underwood (1981) criteria for adequate Na+ supply, whereas that of the C cows was consistent with the criteria for inadequate Na+ supply without clinical signs. The trend toward an increase in urinary ion concentrations and the significant increase in ion excretion suggest that ion intakes in the E cows at week 7 PP was in excess of requirements. However, the fact that the much higher ion intakes in E did not induce diuresis and activation of the renin system suggests that the excess was moderate (Maltz & Silanikove, 1996). Thus the higher ion retentions in E than in C cows suggests that these ions were used to compensate for losses in sweat, saliva dribbling and depletion of body stores. The need of the cows for a particular ion could be roughly estimated as the differences in ion retention between the two groups divided by the apparent absorption. Accordingly, requirements were higher than retention for the C cows by (mmol}d) 647 for K+, 416 for Cl− and 343 for Na+. These could be provided by increasing the concentrations of K+, Cl− and Na+ in the diet to 12, 7 and 3±3 g}kg respectively. The greatest increase needed was in K+, which is consistent with its dominance in sweat secretion (Johnson, 1970 ; Jenkinson & Mabon, 1973). Dietary ion requirements as proportions of the diet are likely to be even higher in early lactation, when milk yields are already high but feed intake not yet increased as much as in later lactation. Greater heat stress and higher milk yields than those that characterized the present experiment would further increase dietary ion requirements (Shalit et al. 1991 ; Silanikove et al. 1997). Water turnover and thermoregulation The main factors that influence free water intake and water turnover in cattle are DM intake, milk yield and RCW loss (Murphy, 1992 ; Maltz et al. 1994 ; Silanikove et al. 1997). Maltz et al. (1994) and Silanikove et al. (1997) demonstrated that the milk free water balance (water turnover rate®water excreted in milk) could be predicted for both dry and lactating cows by an equation that includes digestible energy intake
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and RCW loss as dependent variables (n ¯ 33, R# ¯ 0±96, P ! 0±0001) and discussed its physiological basis. The predicted RCW losses for the conditions of the present experiment, according to eqn (2) in Silanikove et al. (1997), were (l}d) 44±5 for E cows and 42±2 for C cows, in excellent agreement with the values calculated from the water balance results. The lack of differences between the two groups in RCW loss is consistent with the absence of differences in DM intake, digestible energy intake and milk yield at week 7 PP. RCW loss has previously been measured under summer (Shalit et al. 1991) and winter (Silanikove et al. 1997) Mediterranean conditions at 7 weeks PP. The RCW losses in the present experiment were 31 l}d lower than those reported by Shalit et al. (1991). These differences are consistent with the lower milk yield (by 4 l}d) and lower rectal body temperature at noon (38±4 v. 39±4 °C). In the experiment of Shalit et al. (1991), it was suggested that lack of ion availability was most probably a ratelimiting factor in the ability of the cows to sweat. One of the purposes of the present experiment was to test this hypothesis. However, ion supplementation did not improve the thermoregulatory response in E cows, probably because internal and external heat loads were modest. Silanikove et al. (1997) suggested that ion deficiency may still be a rate-limiting factor for milk production, and this possibility was supported by the present results. Kidney function Recently it was concluded that the maximal urinary concentrating capacity (osmotically fixed ceiling) of dairy cows is C 1000 mosmol}kg, and that the kidney function of cows exhibits a classic interdependence mechanism (Maltz & Silanikove, 1996). Interdependence refers to an inversely proportional relationship between urea and non-urea solutes in the formation of maximally concentrated urine. Such a mechanism is consistent with the present results for several reasons. Firstly, the increases in ion load and ion excretion did not affect urine osmolality. Secondly, the increase in ion concentration and reduction in ion tubular reabsorption were associated with an equivalent increase in urea concentration and reduction in urea tubular reabsorption. Thirdly, the reduction in the urine : plasma ratio of creatinine, together with the increase in urine volume in E cows, was consistent with the expected response of such a mechanism when the kidney maximum excretion capacity is moderately exceeded (Maltz & Silanikove, 1996). The negative reabsorption : filtration ratio for K+ in E cows was consistent with the conclusion that there is a capacity for active secretion of K+ in the nephrons of cattle (Maltz & Silanikove, 1996). Thus, as suggested previously (Maltz & Silanikove, 1996), a moderate excess of K+ did not induce copious urine production. The present results further sustain the conclusion that, during summer, the reabsorption of ions by the kidney increases to retain water in the body (Maltz & Silanikove, 1996 ; Silanikove et al. 1997). The increase in maximal concentrating capacity of urine from C 900 mosmol}kg in the winter (Silanikove et al. 1997) to C 1100 mosmol}kg in the summer (Shalit et al. 1991 and the present results) is an adaptive response that allows the cows to lose less water when excreting urea. Lactose and ions in milk Milk is isotonic with respect to the blood ; lactose contributes C 60 % of its osmolality and Na+, K+ and Cl− most of the rest (Peaker, 1977). The increase in lactose concentration by C 8 m in E compared with C cows was consistent with the results of Chiy & Phillips (1991) and Chiy et al. (1993) and with the observed 8±6 m
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reduction in the sum of the concentrations of Na+, K+ and Cl−. The increase in milk lactose concentration in the E cows is needed for osmotic equilibration with systemic fluid, and could have been provided by their higher energy intake at weeks 2–4 PP. Hormonal and metabolite responses IGF-1 is implicated in galactopoiesis (McGuire et al. 1995) and so the larger increase in IGF-1 concentrations in E than in C cows during weeks 2 and 3 PP is consistent with the higher yields of milk, fat, protein and lactose in E cows between weeks 1 and 4 PP. The increase with time in the plasma activities of LDH, GGT, aspartate aminotranferase and 3-hydroxybutyric acid and in the concentrations of plasma cholesterol most probably reflected a parallel increase in liver activity, and the increases in plasma concentrations of total protein, globulin and creatinine reflected an increase in protein metabolism. The higher activity of LDH and GGT and the higher concentrations of cholesterol and creatinine in E than in C cows between weeks 2 and 4 PP probably reflected a greater activity of the liver in the E cows. This is consistent with higher DM intakes and IGF-1 levels during this period. Aldosterone controls Na+ balance by increasing its retention when Na+ is deficient, and K+ balance by increasing urinary secretion when there is a need to excrete a K+ load (Blair-West et al. 1970). Thus, the reduction in aldosterone concentrations in E cows during weeks 2 and 3 is consistent with adjustment of Na+ requirements by the enhanced Na+ intake in this group. The subsequent elevation in aldosterone concentrations in E cows was most probably related to the increased K+ intake and excretion detected at week 7 PP. Angiotensin II, a product of plasma renin, activates the secretion of aldosterone (Young, 1988). Within the kidney itself, angiotensin II has the potential to regulate both haemodynamic and tubular functions (Blair-West et al. 1970). Thus, the lack of difference in plasma renin activity between the two groups is consistent with absence of any differences between the two groups in glomerular filtration rate, urine flow and aldosterone during week 7 PP. In conclusion, we suggest that current nutritional practices impose ion deficiencies in dairy cows in early lactation. Relaxation of such constraints improves the ion status of the cow, and may increase DM intake and milk yield. Improvements in ion balance may explain some of the well known positive responses of cows to the addition of buffers to their diet. This series of investigations (Shalit et al. 1991 ; Silanikove et al. 1997 and the present experiment) demonstrates the need to quantify ion losses via sweat and their relationship with sweating rate and ion status. This information is essential to determine whether, and at what stage, ion supply becomes a rate limiting factor in the capacity of cows to sweat and maintain homeothermia. B, N. G. & T, A. 1991 Effects of sodium carbonate on milk yield, milk composition, and blood components of dairy cows in early lactation. Journal of Dairy Science 74 467–472 B-W, J. R., C, J. P., D, D. A. & W, R. D. 1970 Factors in sodium and potassium metabolism. In Physiology of Digestion and Metabolism in the Ruminant, pp. 300–361 (Ed. A. T. Phillipson). Newcastle upon Tyne : Oriel Press C, C. P. & P, C. J. C. 1991 The effects of sodium chloride application to pasture, or its direct supplementation, on dairy cow production and grazing preference. Grass and Forage Science 46 325–331 C, C. P., P, C. J. C. & B, M. R. 1993 Sodium fertilizer application to pasture. 2. Effects on dairy cow production and behaviour. Grass and Forage Science 48 203–212 C, R. J., B, D. K., T, W. W., I, L. A. & W, C. J. 1982 Influences of environment and its modification on dairy animal health and production. Journal of Dairy Science 65 2213–2227
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E, R. A. 1988 Dietary buffering requirements of the lactating dairy cow : a review. Journal of Dairy Science 71 3246–3266 J, D. M. &. M, R. M. 1973 The effect of temperature and humidity on skin surface pH and ionic composition of skin secretions in Ayrshire cattle. British Veterinary Journal 129 282–295 J, K. G. 1970 Sweating rate and the electrolyte content of skin secretions of Bos taurus and Bos indicus cross-bred cows. Journal of Agricultural Science 75 397–402 MG, M. A., B, D. E., D, D. A. & C, W. S. 1995 Nutritional modulation of the somatotropin}insulin-like growth factor system : response to feed deprivation in lactating cows. Journal of Nutrition 125 493–502 MK, J. K. & C, J. A. 1974 Simplified radioimmunoassay for serum aldosterone utilizing increased antibody specificity. Journal of Clinical Endocrinology and Metabolism 38 622–627 M, E., D, S., K, O., Z, B., S, S. L. & S, R. D. 1992 Comparative responses of lactating cows to total mixed ration or computerized individual concentrate feeding. Journal of Dairy Science 74 2277–2289 M, E. & S, N. 1996 Kidney function and nitrogen balance in high yielding dairy cows at the onset of lactation. Journal of Dairy Science 79 1521–1527 M, E., S, N., S, U. & B, A. 1994 Diurnal fluctuations in plasma ions and water intake of dairy cows as affected by lactation in warm weather. Journal of Dairy Science 77 2630–2639 M, M. R. 1992 Water metabolism of dairy cows. Journal of Dairy Science 75 326–333 N R C 1989 Nutrient Requirements of Dairy Cattle, 7th edn. Washington, DC : National Academy Press P, M. 1977 The aqueous phase of milk : ion and water transport. In Comparative Aspects of Lactation, pp. 113–134 (Ed. M. Peaker). London : Academic Press (Symposia of the Zoological Society of London no. 41) R, J. D., C, T. J. & A, T. J. 1983 Changes of aldosterone in blood serum of dairy cattle during the estrous cycle. Journal of Dairy Science 66 1734–1737 S, W. K., B, D. K. & D, M. A. 1994 a Macromineral element interrelationships and lactational performance. Empirical models from a large data set. Journal of Dairy Science 77 3096–3110 S, W. K., MG, M. A. & B, D. K. 1994 b Macromineral nutrition by heat stress interactions in dairy cattle. Review and original research. Journal of Dairy Science 77 2051–2079 SAS 1982 User’s Guide : Statistics. Cary, NC : SAS Institute S, P. L., B, D. K. & W, C. J. 1986 Responses of lactating cows to dietary sodium source and quantity and potassium quantity during heat stress. Journal of Dairy Science 69 99–110 S, U., M, E., S, N. & B, A. 1991 Water, sodium, potassium and chlorine metabolism of dairy cows at the onset of lactation in hot weather. Journal of Dairy Science 74 1874–1883 S, N., M, E., H, A. & S, D. 1997 Metabolism of water, sodium, potassium, and chlorine by high yielding dairy cows at the onset of lactation. Journal of Dairy Science 80 949–956 U, E. J. 1981 Sodium, potassium and chloride. The Mineral Nutrition of Livestock, 2nd edn, pp. 59–68. Farnham Royal : Commonwealth Agricultural Bureaux W, J. W., M, B. G. & S, T. G. 1991 Changing dietary electrolyte for dairy cows in cool and hot environments. Journal of Dairy Science 74 1662–1674 Y, D. B. 1988 Quantitative analysis of aldosterone’s role in potassium regulation. American Journal of Physiology 255 F811–F822
