Ecological and physio-biochemical parameters of yak in highland conditions of Kyrgyzstan

M. Asylbekov,¹ S. Abdukaimov² and J. Tynaev²

1. Institute of Physiology and Biochemistry, National Academy of Science, 265 Prospect Chui, Bishkek, Kyrgyz Republic
2. Kyrgyzstan Cattle Breeding Institute, Kyrgyz Republic

Introduction

Kyrgyzstan is a mountainous country completely located in a zone of central Tian-Shan. Mountain ranges extend from east to west direction and have heights from 3000 up to 7000 metres above sea level (masl). The mountains are covered with large fields of various meadows, pastures, hay fields, woods, and are inexhaustible sources of medicinal plants, minerals, and representatives of unique kinds of wild fauna. The huge areas of natural pastures and haymaking are distributed as follows: 48% in mountains, 30% in high-mountainous areas, 17% in foothills, and 5% in agricultural valleys. About 52% of grazing fodder comes from spring and autumn pasture, 22% from winter and 26% from summer meadows. However, animals consume only 64% of the total usable natural fodder land in the republic. Thus, there is a huge potential for the development of yak in the republic. Yak production is practically restricted to farms located in mountain and high-mountainous regions.

The transition of the Republic to a market economy and the reform of agricultural sector is a welcome change. There was a sharp reduction in livestock production. Huge pastures and haymaking areas remained unutilised for a long time. Some valuable livestock breeds created through long-term efforts by scientists have completely disappeared. Examples include Tian-Shan sheep, a fine and rough wool breed; the breed of new Kyrgyz horse; the breed of Kyrgyz chicken; and highly productive duck breed; several breeds of pigs; and the Alatau large horned cattle. The population of yak has also decreased by almost 3 times. Certainly, the local farmers kept some animals, but because of the absence of systematic selective breeding effort for their improvement, they have lost important qualities.

The development of yak breeding in Kyrgyzstan, in our opinion, is a high priority activity. The yak are year round forage users, grazing on pastures located at altitudes ranging from 3500 up to 4500 masl. It has been reported that during winter, the loss in live weight for the large horned cattle is in the order of 27.5% and 22–28% for sheep, but only 16.1% for yak.

Despite such advantages of yak breeding, yak breeding and development has not received the level of attention that it deserves. In particular, no study has been done on the physiological and biochemical bases of yak' productivity in the severe mountain conditions of Kyrgyzstan. There is a need to develop theoretical bases to increase the efficiency of yak production. In addition, the botanical and chemical composition of the forage used by yak in different seasons of the year must, in a certain way, relate to the digestive processes in the yak and, in turn, the efficiency with which the animals use these feeds.

Therefore, the study of yak digestive processes, in particular the rumen, in different seasons of the year under natural grazing conditions may provide vital information about metabolism utilisation of the nutrients in these forages, which can subsequently facilitate the development of improved feeding strategies that increase efficiency of utilisation of these feeds.

Materials and methods

The study was conducted at the collective farm of Talas, at an altitude of 3000–4000 masl. Three female yak aged 5 years and weighing 275–280 kg were used. All animals were fitted with rumen fistula and were grazed on natural pasture year round. The following constituted the focus of the study:

1. Chemical structures of forages eaten by yak;
2. pH, number of infusorium, protein, carbon and mineral exchanges in rumen, cellulolytic and proteolytic activity of the rumen liquid; and
3. Dependence of yak live weights on nutrition value of the pastures and rumen metabolism level in different seasons of the year.

Results and discussion

Chemical contents of edible forages

The high mountain forages were sampled from the top ranges of the mountains (Table 1). The highest water content of forages was observed in the spring, but this decreased in the subsequent seasons of the year, reaching a minimum in winter. The highest crude protein level was recorded in summer, and lowest in winter. The highest crude fat content was in autumn and the lowest in winter. Crude fibre was highest in winter and lowest in spring.

Table 1. Chemical contents of highland pasture in different seasons of year (% DM).

Season	Water	Crude protein	Crude fat	Crude fibre	Nitrogen-free extracts
Spring	76.14	14.67	4.35	29.13	42.07
Summer	68.31	17.41	4.15	33.40	33.80
Autumn	35.24	10.31	5.77	34.63	39.57
Winter	24.61	4.66	3.39	36.69	46.39

There was a marked seasonal variation in mineral content of forages (Table 2). Calcium increased in the autumn, reaching a maximum then decreasing to a minimum in winter. The highest level of phosphorus was in spring forages, but it gradually decreased, reaching a minimum in winter forages. Sodium and potassium levels changed in similar pattern to that of phosphorus. However, the reduction in sodium content was less dramatic than that of potassium. The most favourable ratio of calcium and phosphorus was observed in spring and summer forages, but the ratio became undesirable in the winter and autumn seasons because of the high calcium contents. The relationship between calcium and sodium was less than optimum throughout the year, although in winter and autumn it was more or less favourable. The results showed that the forages were generally poor throughout the year. In general, the forages in spring and summer were more nutritive than those in autumn and winter.

Table 2. Mineral contents in pasture in different seasons of year (g/kg DM).

Season	Calcium (Ca)	Phosphorus (P)	P:Ca	Sodium (Na)	Potassium (K)	Na:K
Spring	7.20	2.97	1:2.4	0.32	21.6	1:66.5
Summer	5.36	2.18	1:2.4	0.30	19.26	1:63.4
Autumn	8.88	1.44	1:6.2	0.29	5.28	1:17.9
Winter	4.32	0.64	1:6.7	0.27	3.41	1:12.5

Physiology of rumen digestion

The characteristics of the rumen environment depended on the season (Table 3). The average pH in spring and summer was the same (6.75). Daily pH ranged from 6.62 to 6.87 in spring and 6.57 to 7.00 in summer. The pH increased from autumn to winter, with a daily fluctuation of 6.18 to 7.44 in autumn and 6.98 to 7.22 in winter.

Table 3. Physiological parameters in yak rumen at difference seasons.

Parameter	Season
	Spring	Summer	Autumn	Winter
pH	6.8 ± 0.03	6.8 ± 0.40	6.9 ± 0.06	7.1 ± 0.03
Infusorium (103/mL)	276.0 ± 9.90	456.6 ± 12.6	305.0 ± 11.2	198.5 ± 7.2
Proteinase (%)	7.1 ± 0.31	7.2 ± 0.69	7.8 ± 0.61	6.4 ± 0.18
Cellulosase (%)	15.2 ± 0.60	18.7 ± 0.92	14.3 ± 0.78	9.9 ± 0.19
Total N (mg%)	113.0 ± 3.03	145.7 ± 2.48	139.7 ± 0.86	66.7 ± 1.63
Protein N (mg%)	51.5 ± 3.01	91.5 ± 3.31	85.2 ± 1.10	27.0 ± 1.72
Residual N (mg%)	61.5 ± 0.93	54.2 ± 2.15	54.3 ± 0.51	39.7 ± 1.54
Ammonia (mg%)	38.9 ± 1.00	49.8 ± 0.27	16.2 ± 0.47	11.1 ± 0.68
Total volatile fatty acids (mM%)	10.0 ± 0.32	10.7 ± 0.35	8.1 ± 0.19	6.2 ± 0.20
Acetic acid (%)	70.2 ± 1.24	78.1 ± 1.26	84.5 ± 0.74	76.5 ± 1.05
Propion acid (%)	14.3 ± 0.53	13.7 ± 0.85	10.8 ± 0.53	15.7 ± 0.63
Oil acid (%)	13.0 ± 0.63	7.2 ± 0.45	4.3 ± 0.29	7.0 ± 0.42
Ca (mg/L)	361.4 ± 6.73	474.8 ± 7.00	315.3 ± 6.73	220.4 ± 6.62
P (mg/L)	212.2 ± 4.53	263.4 ± 60.2	217.7 ± 5.28	198.0 ± 4.78
K (mg/L)	1057.7 ± 31.4	1161.5 ± 21.4	976.8 ± 33.4	476.2 ± 16.4
Na (mg/L)	1962.0 ± 14.0	2927.3 ± 13.0	1987.6 ± 15.5	1540.8 ± 13.4

The number of infusorium in yak rumen was also influenced by season-dependent physiological changes. The average number recovered ranged from the lowest (276.0 × 103/mL) in spring, rising to the highest level in summer, before decreasing in autumn. The daily changes of the number were from 262.7 to 295.7 × 10³/mL in spring, from 414.3 to 499.3 × 10³/mL in summer, from 286.0 to 331.0 × 10³/mL in autumn, and from 194.5 to 230.7 × 10³/mL in winter.

In comparison with data from cattle, the pH value in yak rumen was relatively stable across seasons of the year but the number of infusorium was a little bit higher in summer and autumn but much lower in winter than that in the large horned cattle.

The fermentative activity of yak rumen was considerably influenced by season. The highest proteolytic and cellulolytic activities in the rumen fluid were observed in the spring, summer and autumn but the lowest in winter. All other parameters, including total nitrogen (N), protein N, residual N, ammonia, total volatile fatty acids (TVFA), Ca, P, K and Na relating with the rumen fermentation indicated similar seasonal patterns with those of the proteinases and cellulosases. Exceptions are summarised below:

1. The biggest fluctuation in total N was observed in spring from 91.6 to 125.7 mg%; there was much less fluctuation in other seasons. Compared to the situation in large horned cattle, the total N in yak was more in summer and autumn but less in winter.
2. The daily fluctuation in protein N was 35.9 to 63.6 mg% in spring, 83.7 to 101.1 mg% in summer, 76.6 to 90.4 mg% in autumn and 24.8 to 29.0 mg% in winter. Compared with the large horned cattle and sheep, the yak seem to have similar protein N in spring and autumn but higher protein N in summer and less protein N in winter (by 1.5 to 2.5 times).

3. The daily residual N changed from 57.4 to 65.6 mg% in spring, 48.2 to 59.9 mg% in summer, 52.0 to 57.2 mg% in autumn and 37.0 to 42.6 mg% in winter. Thus, highest variation of parameters of residual nitrogen within a single day was observed in the summer. Comparative analysis revealed that the yak had more residual N in spring, summer and autumn but a similar amount in winter compared with sheep. However, the large horned cattle have more residual N than yak in winter.

4. The daily fluctuations of ammonia ranged from 34.2 to 42.7 mg% in spring, 48.2 to 50.2 mg% in summer, 15.2 to 16.8 mg% in autumn and 10.0 to 12.4 mg% in winter. Compared to sheep and the large horned cattle, the yak have more ammonia in spring and summer than in sheep but similar levels to that in cattle.

5. The minimum daily TVFA was observed at 08:00 h and the maximum at 20:00 h. There was no difference between yak TVFA and that of sheep and large horned cattle in spring, summer and autumn. However, the yak TVFA were lower in winter.

6. The daily changes of acetic acid fluctuated from 66.4 to 71.4% in spring, 72.1 to 81.7% in summer, 82.6 to 86.5% in autumn and 75.2 to 78.0% in winter. The comparative data showed that the acetic acid levels in yak rumen in autumn, summer and winter were much higher than in the large horned cattle and sheep.

7. The daily propionic acid in yak rumen changed from 12.7% to 15.9% in spring, 11.4% to 18.1% in summer, 10.2% to 11.1% in autumn and 14.4% to 16.5% in winter. Further comparison indicated that the propionic acid levels in yak were lower in all seasons than that in the large horned cattle and sheep, especially in autumn and summer (lower by 1.5 to 2.5 times).

8. The daily oil acid changed from 12.7 to 16.1% in spring, 5.3 to 8.6% in summer, 2.9 to 6.0% in autumn and 6.4 to 7.4% in winter. Comparing the oil acid levels in yak rumen with other animals, the possible conclusion was that the maximal concentration in yak in spring corresponded to the minimal value of the large horned cattle and sheep, but the daily average concentration of the oil acid in yak rumen in other seasons was lower than that in sheep and large horned cattle.

9. The Ca contents in yak rumen were much lower than for other animal species.

10. The concentration of P was influenced by season. In spring, in spite of the fact that the forages may supply much more P than in other seasons, the P in yak rumen was lower than that in summer or autumn. The daily P value changed from 190.7 to 223.2 mg/L in spring, 230.1 to 318.3 mg/L in summer, 206.5 to 226.0 mg/L in autumn and 181.6 to 212.3 mg/L in winter. The minimal concentration in all seasons of the year was marked in the morning hours and maximal at night. The P contents in yak rumen were much lower than that in the large horned cattle and sheep, but the fluctuations were smaller.

11. The K concentrations in yak rumen in spring, summer and autumn seasons were lower by 2 times, and in winter by 4 to 5 times than that in sheep and large horned cattle.

12. The Na contents in yak rumen corresponded to that in other animal species.

Live weight of yak

There were differences between seasons in yak live weights. The highest live weight was observed in the summer with an average of 284.0 ± 14.2 kg. This was followed by a decrease to 278.8 ± 3.78 kg in autumn and down to 246.2 ± 1.84 kg in spring and finally to the lowest of 240.5 ± 3.10 kg in winter. Thus, the greatest weight loss was from middle of October to the end of April.

Recommendations

Unlike the large horned cattle, which usually breed the year round, the oestrus of yak occurs only from July to August and the gestation period averages 257 days. Hence, the calving time is around March to April. Therefore, it is necessary to supplement in-calf animals in this period, especially in last three months of pregnancy. We recommend that a supplement of 3 kg of mountain hay and 2 kg of straw/animal per day.