The effect of high ambient temperature on Ca, P and Mg balance and bone turnover in high-yielding dairy cows
ABSTRACT
We investigated the effect of heat stress on Ca, P and Mg balance and bone turnover in lactating cows. In a 2 × 2 crossover design, four multiparous lactating Holstein cows were kept in a chamber and subjected to a constant moderate (18°C) ambient temperature (MT) or high (28°C) ambient temperature (HT). The cows were fed total mixed ration (Ca, 0.7%; P, 0.4%; Mg, 0.2%) ad libitum. The milk yield under HT (35.4 kg/day) tended to be lower (P < 0.10) than that under MT (43.2 kg/day). The concentrations of milk P (P < 0.05) and Mg (P < 0.01) were significantly lower under HT than MT. The Ca, P and Mg intake (P < 0.10); Ca (P < 0.10), P, and Mg (P < 0.05) secretion into milk; and Ca (P < 0.05), P (P < 0.01), and Mg (P < 0.05) absorption in the intestine were lower under HT than MT. The plasma osteocalcin, a marker of bone turnover, was significantly lower (P < 0.05) under HT than MT. Heat stress did not affect plasma C-telopeptide of collagen type I, a bone resorption marker, and plasma parathyroid hormone concentration.
INTRODUCTION
Lactating dairy cows prefer ambient temperatures between 5 and 25°C as a thermoneutral zone (Roenfeldt 1998). In the southern part of Japan, the average temperature rises above 25°C from June to September; therefore, the dairy cows in this area are affected by heat stress for 4 months per year. Heat stress alters the requirement of specific nutrients for physiological processes and metabolism in dairy cows (Beede & Collier 1986). It is well known that heat stress reduces dry matter intake (DMI), milk yield, and composition of dairy cows (Shibata 1983; Rodriquez et al. 1985; Kamiya et al. 2005), and it can also affect major mineral nutrition in dairy cows (Sanchez et al. 1994). In dry cows, the intake and retention of major minerals were depressed by heat stress (Kume et al. 1986). In lactating dairy cows, the intake and apparent absorption of major mineral were depressed by heat stress (Kume et al. 1987). Around parturition, plasma osteocalcin (OC) concentration measured as a marker of bone turnover in cows under high ambient temperature was lower than those under moderate ambient temperature (Kamiya et al. 2006a). However, the relationship among heat stress and Ca, P and Mg balance, and bone turnover in dairy cows, especially in high-yielding cows, is still unclear. Therefore, this study was conducted to clarify the effects of heat stress on Ca, P and Mg balance, milk and plasma Ca, P and Mg, and bone formation and resorption markers in high-yielding dairy cows.
MATERIALS AND METHODS
Experimental design
Four multiparous lactating Holstein cows after peak lactation period (average body weight: 638 kg) were assigned to either of two ambient-temperature groups in a 2 × 2 crossover experimental design: constant moderate ambient temperature (MT group: 18°C; relative humidity (RH): 60%) or high ambient temperature (HT group: 28°C; RH: 60%). Each cow was housed individually in a humidity- and temperature-controlled chamber (Kurihara et al. 1989; Mukai et al. 1989). The experiment consisted of two 21-day experimental periods, each comprising a 7-day no-treatment period, 9-day treatment-adaptation period, and a 5-day balance trial. The chemical compositions of the total mixed ration (TMR) were 72.3% total digestible nutrients, 15.1% CP, 33.1% neutral detergent fibers, 0.4% P, 0.7% Ca and 0.2% Mg. All procedures used in this study were examined and approved by the Annual Research Project Examination Committee of the National Agricultural Research Center for Kyushu Okinawa Region.
Balance trial
The TMR was offered at 08.30, 10.30, 16.00 and 18.00 hours to both treatment groups ad libitum. Food refusals were collected daily before the 10.30 hour feed for a 5-day period (days 17–21 of each experimental period) and were bulked for analysis. Feces and urine were collected and weighed daily at 10.30 hour for a 5-day period and were bulked for analysis. The cows were milked at 08.30 and 18.00 hours. The milk yield was recorded daily, and milk samples were collected during each milking for compositional analysis. Blood samples were taken from the jugular vein through a heparinized tube at 10.30 hour on the final day of the trial period. Plasma was separated by centrifugation at 1500 × g for 15 min. All samples were stored at –20°C until analysis.
Sample analysis
For analysis of Ca, P and Mg, diets, milk, feces, and urine were digested in nitric–perchloric acid, and plasma was deproteinized with 10% trichloroacetic acid. The P content in each sample was determined by using the colorimetric methods of Gomori and Ill (1942). The concentrations of Ca and Mg in each prepared sample were determined by atomic absorption spectrophotometry (SOLAAR M6, Nippon Jarrell-Ash Co., Ltd, Kyoto, Japan). The intact parathyroid hormone (PTH) concentrations in plasma were determined by radioimmunoassay using a commercial kit (Nichols Diagnostics, San Juan de Capistrano, CA, USA). OC concentrations were measured using a commercially available radioimmunoassay kit (Yuka Medias Co., Ltd, Ibaraki, Japan). Plasma C-telopeptide (CTx) fragments of type I collagen were measured using a commercial ELISA kit (Fujirebio Inc, Tokyo, Japan). This assay detects collagen type I fragments containing Glu-Lys-Ala-His-Asp-β-Gly-Gly-Arg peptides (Rosenquist et al. 1998).
Statistical analysis
The data were analyzed statistically according to the crossover design by using the general linear model procedure of SAS (1999), with the cows' treatment as the effects. The treatment was considered to be significantly different if the P-value was <0.05 and tends to be different if the P-value was <0.10.
RESULTS AND DISCUSSION
The DMI of the cows under HT (19.6 ± 1.2 kg/day) tended to be lower (P < 0.10) than the cows under MT (24.6 ± 1.2 kg/day). The mean value of DMI under HT was lower by approximately 20% compared to those under MT. The milk yield of the cows under HT (35.4 kg/day) tended to be lower (P < 0.10) than of the cows under MT (43.2 kg/day) (Table 1). The average milk yield of the cows under HT was lower by approximately 18% compared with the cows under MT. Kurihara et al. (1995) summarized that milk production was reduced by 5–20% during summer in the Kyushu district; therefore, our results indicated that the cows under HT had relatively severe heat stress in this study. The milk P (P < 0.05) and Mg (P < 0.01) concentrations of the cows under HT were significantly lower than those cows under MT (Table 1). Kume et al. (1987) also reported that the Mg and P concentrations in milk of the cows in the temperature-controlled chamber (18, 26 and 30°C) tended to decrease with higher temperature.
| 18°C | 28°C | SE | |
|---|---|---|---|
| Milk yield (kg/day) | 43.2 | 35.4 | 1.8* |
| Milk Ca (mg/dL) | 95.3 | 96.0 | 0.3 |
| Milk P (mg/dL) | 91.5 | 84.9 | 1.1** |
| Milk Mg (mg/dL) | 10.2 | 8.9 | 0.1*** |
- * P < 0.10;
- ** P < 0.05;
- *** P < 0.01.
Table 2 shows Ca balance of the lactating cows under HT and MT. The Ca intake and Ca secretion into milk of the cows under HT tended to be lower (P < 0.10) than the cows under MT. The apparent absorption of Ca in the intestine of the cows under HT was significantly lower (P < 0.05) than the cows under MT. Environmental temperature did not affect Ca excretion into feces, urine, Ca retention, and Ca digestibility of the cows. Phosphorus balance of the dairy cows under HT and MT is summarized in Table 3. The heat stress decreased P intake (P < 0.10) and P secretion into milk (P < 0.05). Apparent absorption of P of the cows under HT was significantly lower (P < 0.01) than those under MT. The environmental temperature did not affect P excretion into feces, urine, P retention, and P digestibility of cows. Table 4 shows the Mg balance of the dairy cows under HT and MT. The Mg intake tended to be lower (P < 0.10) in the cows under HT than those under MT. The Mg secretion into milk of the cows in HT was significantly lower (P < 0.05) than that in MT. Apparent absorption of Mg of the cows under HT was significantly decreased (P < 0.05) compared to those under MT. The environmental temperature did not affect Mg excretion into feces, urine, Mg retention and Mg digestibility of the cows. These results suggest that heat stress adversely affects the intake, secretion into milk and absorption in the intestine of P, Ca and Mg.
| 18°C | 28°C | SE | |
|---|---|---|---|
| Intake (g/day) | 175.9 | 137.7 | 9.2* |
| Excretion (g/day) | |||
| Feces | 114.8 | 89.4 | 8.8 |
| Urine | 4.0 | 1.8 | 1.1 |
| Milk | 41.2 | 34.0 | 1.8* |
| Apparent absorption (g/day) | 61.2 | 48.4 | 2.5** |
| Retention (g/day) | 16.0 | 12.6 | 3.7 |
| Digestibility (%) | 34.9 | 35.6 | 2.3 |
- * P < 0.10;
- ** P < 0.05.
| 18°C | 28°C | SE | |
|---|---|---|---|
| Intake (g/day) | 89.6 | 72.8 | 4.1* |
| Excretion (g/day) | |||
| Feces | 47.6 | 39.6 | 3.4 |
| Urine | 0.2 | 0.2 | 0.0 |
| Milk | 39.6 | 30.4 | 1.5** |
| Apparent absorption (g/day) | 42.0 | 33.2 | 0.7*** |
| Retention (g/day) | 2.2 | 2.6 | 0.8 |
| Digestibility (%) | 47.0 | 45.5 | 1.2 |
- * P < 0.10;
- ** P < 0.05;
- *** P < 0.01.
| 18°C | 28°C | SE | |
|---|---|---|---|
| Intake (g/day) | 49.0 | 39.3 | 2.2* |
| Excretion (g/day) | |||
| Feces | 32.7 | 26.8 | 2.0 |
| Urine | 7.3 | 5.4 | 0.8 |
| Milk | 4.4 | 3.1 | 0.2** |
| Apparent absorption (g/day) | 16.3 | 12.5 | 0.8** |
| Retention (g/day) | 4.7 | 4.0 | 0.7 |
| Digestibility (%) | 33.2 | 31.6 | 1.8 |
- * P < 0.10;
- ** P < 0.05.
Table 5 shows the plasma Ca, P, Mg, OC, CTx and PTH concentrations of the cows under HT and MT. There were no significant differences in the plasma Ca, P and Mg concentrations of the cows under HT and MT. The plasma P concentrations of the cows under both HT and MT were a little lower than the range (4–8 mg/dL) considered to be normal (Forar et al. 1982). The plasma Ca concentrations of the cows under both HT and MT were within the normal range (7.8–10.5 mg/dL) as defined by Goff et al. (1996). The heat stress did not affect the plasma PTH concentrations of the cows. The plasma OC concentration was significantly lower (P < 0.05) in the cows under HT than those under MT. The plasma OC level was well correlated with osteoblast function, bone formation, or turnover (Farrugia et al. 1989; Naito et al. 1990; Liesegang 2003). The low level of plasma OC concentration in HT suggested that heat stress adversely affects the bone formation activity. The plasma CTx level was not affected by the heat stress. The plasma CTx is a breakdown product of type I collagen and is considered to be a useful marker of bone resorption in the lactating cows (Liesegang 2003; Holtenius & Ekelund 2005). Our results indicated that heat stress does not have an apparent effect on the bone resorption activity. This was not similar to the observation of Kawashima and Yano (1988), who reported that heat stress had apparent effects on both bone formation and resorption markers in growing rats.
| 18°C | 28°C | SE | |
|---|---|---|---|
| Plasma Ca (mg/dL) | 9.7 | 9.6 | 0.3 |
| Plasma P (mg/dL) | 3.5 | 3.5 | 0.4 |
| Plasma Mg (mg/dL) | 1.9 | 1.8 | 0.1 |
| Plasma OC (ng/mL) | 9.7 | 6.8 | 0.3* |
| Plasma CTx (ng/mL) | 2.4 | 2.8 | 0.3 |
| Plasma PTH (pg/mL) | 179.4 | 66.4 | 56.6 |
- * P < 0.01. OC, osteocalcin; CTx, C-telopeptide; PTH, parathyroid hormone.
In this study, the intake and milk secretion of Ca, P and Mg under HT was lower than those under MT. This is owing to the decrease in milk and DMI under HT compared with those under MT. The apparent absorption of Ca, P and Mg under HT was lower than those under MT, which is in agreement with the previous reports (Kume et al. 1987; Kume 1991). The Ca, P and Mg balance in this study were positive in both groups. Kume et al. (1987) suggested that the net requirement of Ca, P and Mg for lactation under HT decreased because heat stress decreased milk yield. Our results suggested that the dietary mineral intake was sufficient to meet the requirements of the cows for milk secretion both under HT and MT. However, the milk P and Mg concentrations of the cows under HT were lower than those under MT, which suggested that the utilization of P and Mg was reduced by the heat stress (Kume et al. 1989).
The plasma OC, a marker of bone formation, of the cows under HT was lower than those under MT. On the other hand, plasma CTx, a marker of bone resorption, was not affected by the heat stress. Liesegang et al. (2000) reported that the cows with a higher milk yield had a higher bone formation and resorption rate than the cows with a lower milk yield. In addition, they showed that the carboxyterminal telopeptide of type I collagen as a bone resorption marker could be highly influenced by milk yield and indicated that more Ca is present in milk of the cows with a higher milk yield. However, there were no differences in the Ca, P and Mg retention and bone resorption markers between the cows under HT and MT. The positive balance of these minerals suggested that bone minerals were not much mobilized for milk secretion in both groups. The results of bone formation and resorption markers indicated that the Ca, P and Mg balance of the cows under HT would be lower than those under MT. There were no differences in the Ca, P and Mg retention between the cows under HT and MT. Some researchers (Kamiya et al. 2006b; Taylor et al. 2009) have reported that plasma OC as a bone formation marker and plasma or urinary deoxypiridinoline as a bone resorption marker did not have an apparent relationship with dietary Ca and P, and Ca and P balance. Bone is a dynamic tissue that is constantly being resorbed and formed. The change in the direction of plasma bone formation and resorption markers might be an indicator of a net change of bone mass, but our data did not reflect the Ca, P and Mg balances. However, the results of bone formation markers suggested that anabolic action on bone of the cows under HT was lower than those under MT. Heat stress would have an adverse affect on bone metabolism. There was no significant difference in the plasma PTH concentration between the cows under HT and MT. In the cows, serum PTH typically increases around parturition, activating bone resorption, renal Ca resorption and intestinal Ca absorption via vitamin D, to maintain plasma Ca levels (Horst 1986). Heat stress did not affect the plasma Ca and P levels; therefore, PTH is supposed to play only a minor role on Ca and P mobilization in this study.
In conclusion, the Ca, P and Mg intake, absorption in the intestine and secretions to milk of the cows under HT was lower than under MT. Milk P and Mg concentrations of the cows under HT were significantly lower than those under MT, which indicated that P and Mg utilization is affected by heat stress. The bone formation activity of the cows under HT was decreased compared to those under MT. Therefore, under HT, it is necessary to improve the nutritional management of dairy cows, especially for high-yielding dairy cows.
ACKNOWLEDGMENTS
The authors thank the staff of the dairy farm at the National Agricultural Research Center for Kyushu Okinawa Region for their technical help and assistance in collecting samples.
