Seasonal changes in forage nutrients and mineral contents in water resources, forage and yak blood

Y. Ping,¹ Zh. Dejuan,¹ X. Xishan,¹ P. Heping² and Ch. Shengli¹

1. Lanzhou Institute of Animal and Veterinary Pharmaceutical Sciences, Chinese Academy of Agriculture Sciences, Lanzhou 730050, Gansu, P.R. China 
2. Food and Animal Science Department, North-West College for Nationalities Lanzhou 730050, Gansu, P.R. China

Summary

This paper reports results of a study conducted to investigate the concentrations of seven mineral elements in yak blood, forage and water resources around the Qinghai Lake in Qinghai Province in different seasons. Meanwhile, the nutritional compositions of the forage were also surveyed. The results suggest that the mineral elements and the forage nutrients change in a seasonal pattern. In yak blood, the sodium (Na) concentration varies from 0.291 to 0.034 mg/mL, and this is lower than the normal value. In the forage, the ratio calcium (Ca) to phosphorus (P) is 4.06–7.47:1 and potassium (K) to Na 30–27:1. These results indicate that the nutrition of the yak in the area is deficient in Na but high in K. For the withered forage sampled in February, the protein content is only 31.14% of the total protein in the forage growing at puerile stage in June. The severe loss of protein by 68.9% and decrease of effective nutrients in the wintered forage are considered to be the reasons resulting in the poor condition of yak in winter and spring seasons. 

Keywords: Forage, mineral elements, nutrients, water, yak

Introduction

Yak grazing under prolonged harsh conditions have developed the adaptability to tolerate the poor fodder supply in winter and spring. However, little is known about their nutritional status in terms of mineral contents in both yak blood and the animal's feed and water supply in different seasons. The understanding of changes of mineral elements in forage, water resources and yak blood, and the changes of nutritional compositions in the forage can be useful pieces of information in developing nutritional management strategies. The objective of this study was to investigate the concentration of seven mineral elements in yak blood, forage and water resources in different seasons of the year.

Materials and methods

Background of the study sites

The experiment was done in the state-owned Sanjiaocheng sheep farm located in Gangcha County of Qinghai Province, near the Qinghai Lake. The altitude is above 3200 metres above sea level (masl), the annual average temperature –6°C, the verdant period of 108 days, the annual rainfall 370 mm, and the annual evaporation 1607 mm.

Sampling date

The study was done from October 1997 to June 1998 and samples were collected in June, October and February. These three sampling dates were the periods corresponding to growth stage of forage in puerile, on growth end and in withered time, respectively.

Measurements

The forage samples were collected by multiple dotted cutting and then mixed for measuring the nutrients. Ten healthy yak were selected randomly and then earmarked to sample the blood during the three measurement periods for mineral content analyses. Seven kinds of mineral elements in yak serum, water resources and the forage were measured.

Results and discussion

Crude protein in the forage is 15.22% at its puerile stage and 6.83% at growth stage. At withered stage, it is 4.74%, which is 31.14% of that at the puerile stage. The crude fat content changes in the same pattern. Crude fibre, ash and Ca increase with forage growth. The extractions of non-nitrogen vary from 43.79–51.71%. The content of Ca and the ratio of Ca to P change as crude fibre (Table 1).

Table 1. Nutrient composition of forages studied(%).

Period	DM	CP	F	CF	NNE	Ash	Ca	P	Ca/P
June	89.91	15.22	3.83	20.38	43.79	5.88	0.65	0.16	4.1:1
October	92.91	6.83	2.98	23.93	51.71	6.38	0.93	0.14	6.0:1
February	92.07	4.74	2.85	26.00	48.99	8.31	1.04	0.16	7.4:1
DM= dry matter; CP = crude protein; F = fibre; CF= crude fat; NNE= non-nitrogen extracts; Ca= calcium; P= phosphorus.

The mineral contents in water resources and forage vary seasonally and they could meet yak growth and development requirements, except Na that is lower than yak requirements (Tables 2 and 3). The highest Na content per kilogram forage is 244.6 mg, and per mL water is 155.2 mg. This is far lower than the normal requirement (Qiu et al. 1989). In addition, the K:Na ratio in the forage (30–27:1) is higher than the normal range of 5:1 (Jiang et al. 1993).

Table 2. Mineral contents in water resources (΅g /mL).

Date	Cu	Fe	Zn	Ca	Mg	K	Na
June	0.002	0.023	0.031	8.64	169	0.612	155.2
October	0.001	0.050	0.010	24.05	0.376	2.29	8.16
February	0.004	1.500	0.080	92.5	3.14	0.58	0.41
Cu = copper; Fe= iron; Zn = zinc; Ca = calcium; Mg = magnesium; K = potassium; Na = sodium.

Table 3. Mineral contents of forages studied (mg /kg).

Period	Cu	Fe	Zn	Ca	Mg	K	Na
June	6.93	430.4	29.7	4960	2050	7562	244.6
October	2.37	280.4	9.6	6450.5	163.5	3525	120
February	8.08	334.5	37	24150.6	6625	2932.5	107
Cu= copper; Fe = iron, Zn = zinc; Ca = calcium; Mg = magnesium; K = potassium; Na = sodium.

The mineral contents in yak blood vary between seasons except copper (Cu) (P<0.01) whose levels in serum are not significantly different among the three sampling periods and are lower than the normal range of 0.8–1.2 ΅g/mL. Na level is also much lower than the normal range of 3.3–3.4 mg/mL (Ni and Wang 1994). The other mineral concentrations are in the normal range for yak growth and development (Table 4).

Table 4. Mineral content of yak serum (΅g /mL).

Period	No.	Cu	Fe	Zn	Ca	Mg	K	Na–
June	10	0.374	3.168c	2.765bc	99.743a	29.199ab	170.19c	291.045a
October	10	0.404	5.865a	7.618a	87.858b	31.983a	279a	200.816b
February	6	0.405	4.249b	2.814b	85.5bc	26.799bc	195.45b	34.10c
F-test	10	P>0.05	P<0.01	P<0.01	P<0.01	P<0.01	P<0.01	P<0.01
Cu = copper; Fe = iron; Zn zinc; Ca = calcium; Mg = magnesium; K = potassium; Na = sodium; Superscripts in the same column differ from each other.

From the results of the study, it is suggested that the supplementary mineral blocks containing Na, P and Cu should be given to yak in the area to facilitate normal yak growth and development. This should also improve the overall health of the animals (Zhang 1998).

References

Jiang Jingchuen, Li Ming and Hu Weiyu. 1993. Studies on grass production of Hulun Beier grassland and nutrition matter content. Journal of Chinese Grassland 2:32–35.

Ni Youde and Wang Hai. 1994. The mineral nutrition of livestock and agriculture. Shanghai Science and Technology Press, Shanghai, P.R. China. pp. 50–198. [in Chinese].

Qiu Huai, Zhang Zhiyi and Wu Xiao. 1989. Analysis on herbage nutrition composition in Anxi grassland. Journal of Chinese Cattle 3:50–58.

Zhang Caijun. 1998. Studies on sodium and potassium nutritional status of sheep around the Qinghai Lake in Qinghai Province. Chinese Journal of Qinghai University 16:9–12.