Effect of parity in different grazing seasons on milk yield and composition of cattle × yak hybrids in the Himalayan alpines

ABSTRACT

This study assessed the effect of parity in different seasons on the milk yield and composition of lactating cattle × yak hybrids (Dimjo Chauries) in the Nepalese Himalayan alpines. A pasture site typically grazed in summer and autumn was selected at 4200 m.a.s.l. The experimental animals were grouped into 2nd, 4th, and 6th parity groups (n = 18). The pasture characteristics, and milk and body parameters of the animals were measured in both seasons. Parity and season had a significant effect on the body weight of lactating hybrids, and almost constant daily weight gain was observed in 4th parity Chauries. The daily milk yield and fat content were affected by both season and parity, whilst parity did not affect milk protein or lactose content. The highest daily milk yield was obtained from the 6th parity Chauries in summer (3.42 kg day⁻¹) with unchanged fat content, and the lowest (1.46 kg day⁻¹) was from the 2nd parity in autumn. This implies that the older parity cattle × yak hybrids, especially of the 4th parity, are promising for persistently higher milk yield and composition than that of 2nd and 6th parity hybrids.

KEYWORDS:

• Dimjo Chauries
• high mountains
• Himalayan alpines
• transhumance

Introduction

Hybridization of cattle (Bos taurus) with yaks (Bos grunniens) is traditional in the herding communities in the Himalayan alpines of Nepal (Palmieri 1987; Bishop 1989). The female hybrids thus produced, locally called Dimjo Chauries, are fertile (Palmieri 1987) and serve multiple purposes (Phillips et al. 1946). They form one of the sources of livelihood (Thapa 2002; Guo et al. 2012), and are kept under traditional transhumance system (Wilson 1997). In the transhumance system, animals utilize the rangelands of higher altitudes during summer, and gradually move towards lower altitudes in winter (Degen et al. 2007; Dong et al. 2009). The intensity of animal movement and camping for herding at different pastures varies by animal species, pasture availability, and prevailing weather conditions and altitude of the pasture sites. The cattle × yak hybrids have a similar high altitude tolerance to that of purebred yaks, but have higher milk yield, even at lower altitudes (Barsila et al. 2014), when managed under low stocking density (Barsila et al. 2015). Hybrids have an advantage of heterosis in milk yield and fat content over that of purebred yaks (Wang et al. 1994). The cattle × yak hybrids have better feed utilization efficiency than cattle (Wang et al. 2011), e.g. in terms of roughage utilization (Bao et al. 2011), which might be attributed to its yak parent. In addition, other milk quality characteristics of the offspring can be attributed to either the yak or cattle parent e.g. higher minerals and essential amino acids content (Li et al. 2010, 2011), with some compounds having anti-inflammatory properties (Mao et al. 2011; Nikkhah 2011). Moreover, some milk properties of its yak parent’s e.g. essential fatty acids, vary between seasons and parity (Liu et al. 2011), but it differs in its hybrid off-spring (Marquardt et al. 2018). Information on the milk yield potential of cattle × yak hybrids across the grazing season is limited, as these animals are kept in transhumance in remote areas of the Himalayan mountains of Nepal. In the Kanchenjunga Conservation Area of Nepal, the herders of Olangchung Gola usually bring the herd to 4200 m (Mauma pastures) in July during upward movement and the same sward is also grazed in September, during the downward movement. Scientific evidence suggest that older parity cattle and their crossbreeds are more resilient to lower forage quality and availability. However, limited research is available on the effects of parity and grazing season on milk yield and composition of cattle × yak hybrids reared in the Himalayan alpine rangelands of Nepal. The milk yield and composition of cattle × yak hybrids might be influenced by the seasonal changes and parity in the alpine transhumance settings. It is hypothesized that, with the increase in parity, there is an increase in milk production, and further expected that the older parity cattle × yak hybrids are more resilient than younger ones to the consumption of low-quality herbages during grazing in the Himalayan alpines, whilst maintaining the milk yield and quality.

Materials and methods

Experimental design

Site selection

In the Kanchenjunga Conservation Area (KCA) of Nepal, a traditional transhumant route was identified in consultation with the local herders and a high altitude (4200 m) pasture was selected. There were more than 20 different pasture sites (covering about 15 km in length at an elevational of 2000-5000 m.a.s.l.) available at different altitudes along the transhumant route. The pasture site is free for grazing to the local herders and herds usually arrive by July from the lower altitude pasture sites and again in September during the gradual downward movement.

The experimental pasture site ∼40 ha in size and was always grazed by purebred yaks and their hybrids with cattle during upward (seasonal vegetation) and downward (re-growth of vegetation) movement of the transhumance cycle. The main entry point was fenced to prevent alteration of the vegetation in both the July and September experiments.

Weather record

A portable weather station was manually installed for both measurement periods i.e. in July and September. Weather variables, such as temperature, humidity, and rainfall, were recorded for a limited experimental period (15 days) during both experimental periods. The maximum temperature recorded was ∼18°C in summer (July) and the minimum temperature in September was ∼2°C. The average relative humidity was ∼71% and ∼55% in July and September, respectively. There was ∼5 mm of rainfall in June, whilst it was only ∼0.5 mm in September.

Animal ethics

Nepal has not yet officially established a system for ethical approval of animals in experiments. All the processes involving animals followed the international guiding principles listed by the Council for International Organizations of Medical Sciences and the International Council for Laboratory Animal Science (2012).

Selection of animals

The cattle × yak hybrids used in the experiments were traditionally hybridized off-spring of female Nepalese yaks, called naks (Bos grunniens), and male Tibetan cattle (Bos taurus), managed in the transhumance system. The experimental lactating cattle × yak hybrids were selected and assigned to 2nd, 4th, and 6th parity groups.

When the herd arrived at 3200 m (June) during the upward transhumance movement, a herd milk production record was established and daily milk yield was recorded for 15 days to select the experimental animals. Further information on parturition and parity were obtained from the local herder.

Milking hybrids of 2nd, 4th, and 6th parities were selected based on the similarity of milk yield within parity groups from the same herder. The average milk yield of the 2nd parity group was ranging from 2.29 to 2.35 kg/day, 2.45 to 2.50 kg/day for 4th parity and it remained 2.57–2.60 kg/day for the 6th parity groups. The animal selection was further marked at the similarity in the date of parturition that did not exceed more than a week within each parity group (Table 1). Each group consisted of six lactating hybrids, selected from a herd of 60 animals. The selected animals were kept with the herd throughout the experimental period (July and September) and were used for data collection (milk yield and composition) in July and September, without altering the traditional transhumance practices of the herder. Details of the selection of milking cattle × yak hybrids are shown in Table 1.

Table 1. Description of selection of cattle × yak hybrids and their parity for the experiment in 2017.

Parity	Number of Animals	Milk yield, kg day^−1	Body weight kg	Calving date
2nd	2	2.29	233	15th April
	2	2.31	230	20th April
	2	2.35	231	22th April
4th	2	2.45	244	16th April
	2	2.47	245	19th April
	2	2.50	242	22th April
6th	2	2.57	256	15th April
	2	2.59	257	18th April
	2	2.60	254	21st April

Estimation of aboveground herbage mass and botanical composition

Herbage mass measurements in the swards were carried out in July (summer) and September (autumn; re-growth) in the same pasture during upward and downward movement, respectively. One day before the herd arrived at the experimental pasture site at 4200 m, the botanical composition and plant cover were estimated from 50 random transects of 1 m × 1 m, using the Braun-Blanquet cover-abundance scale (Bonham 2013). The herbage was harvested above 2 cm from the ground and weighed for green mass accordingly to the botanical groups. The herbage samples were mixed together and oven-dried at the Animal Nutrition Laboratory of Agriculture and Forestry University, Nepal, and later the herbage dry mass was calculated.

Analysis of the herbage chemical composition

The representing forage samples were later oven-dried at 60°C until it reached a constant weight, then milled to a 45 mm mesh size. Chemical analyses were performed following the methods of AOAC (1997) and Van Soest (1991) at the laboratory of the Division of Animal Nutrition of Nepal Agricultural Research Council, Khumaltar, Lalitpur, Nepal. The major components analyzed were: organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), and acid detergent lignin (ADL). Moreover, hemicellulose and cellulosic content were calculated.

Measurement of body weight

Body weight was measured on the day when the herd arrived at 4200 m by using a digital balance (max. capacity of 500 kg and 99.9% accuracy). The body weight of the experimental animals was measured again in August (after 30 days) whilst the herd was at 4500 m in the intermediary pastures of the same transhumance route during upward movement. The final body weight measurement was done in September during the autumn phase of the experiment, during the downward movement. The daily weight gain was calculated twice i.e. for the initial 30 days (body weight in August-body weight in July) and for the final 30 days (body weight in September- body weight in August).

Daily milk yield record and analysis of milk composition

Daily milk yield and composition were analyzed for seven days during both measurement periods following a 15 day adaptation period each time. Lactating hybrids were hand-milked by the same herder, without calves, both in the morning (7:00 am) and evening (17:00) accordingly to the herder's traditional practice. The daily milk yield (morning and evening) was recorded using a digital balance (max. capacity of 5 kg and an accuracy of 99%). The milk composition was analyzed with a solar power-operated ultrasonic milk Lactoscan (Milkotronic Limited, Bulgaria). Further, energy-corrected milk by following ALP (2013), daily fat, protein, and lactose yields were calculated. The aliquot technique was used to calculate the milk constituents from a total of the morning and evening milk yield and constituents data, following Barsila et al. (2015).

Statistical analysis

The milk yield and composition data obtained were analyzed without calibration (see Barsila et al. 2014) as the sites were in remote areas where transport of milk to nearby research stations was impossible.

In the statistical analyses, two variable factors i.e. parity and season (represented by grazing month) and their interaction were considered. Further, only the seasonal effect on herbage mass productivity and botanical groups of the herbages was considered. Data were analyzed using the mixed procedure of SAS (version 9.1). The mean differences were obtained at the 5% level of significance using Tukey’s test. The following two-way analysis of variance model was designed for the analysis of milk yield and composition:(1) ${\text{Y}}_{\mathrm{ijkm}}=\mu +{\text{s}}_i+{\text{p}}_j+\text{s}{\text{p}}_k+{\text{e}}_{\mathrm{ijkm}}$(1) Where, Y_ijkm = Individual observation for parameter Y_ijkm; µ = Overall mean for parameter Y;

s_i = Fixed effect of the ith season(month); p_j = Fixed effect of the jth parity; sp_k = Fixed effect of the kth season (month) and parity interaction; e_ijkm = Residual error.

For herbage mass and botanical composition, the following one-way analysis of variance model was used for data analysis:(2) ${\text{Y}}_{\mathrm{ij}}=\mu +{\text{m}}_{\mathrm{j}}++{\text{e}}_{\mathrm{ij}}$(2) Where,Y_ij = Individual observation for parameter Y_ij; µ = Over all mean for parameter Y; m_i = Fixed effect of the ith season (month); e_ij = Residual error.

Results

Pasture characteristics

Herbage cover

Altogether, 65 different vascular plant species were recorded (excluding unknown ferns and algae), whilst 60 could be identified to species level and 15 to genus level only. A shift in herbage cover from herbs (forbs) to grasses and cyperus was observed. Among the highly abundant herbage species, Poa himalayana and Ranunculus hirtellus covered 30% of the area; whilst in September, Kobresia nepalensis and P. himalayana were dominant. Details of the herbage cover are presented in Table 2.

Table 2. Herbage cover and dominant herbage species over two seasons in the pasture site at 4200 m above sea level in the Kanchenjunga Conservation Area of Nepal.

Season	Herbage cover (%)	Dominating herbage species
	Category	Species	Family	Growth stage
July (summer)	n  = 65 different vascular plant species (n = 25 sampling plots)
	>30	Poa himalayana	Poaceae	Vegetative
		Ranunculus hirtellus	Ranunculaceae	Flowering
	20–30	Rumex nepalensis	Polygonaceae	Vegetative
	10–20	Kobresia nepalensis	Cyperaceae	Vegetative
	0–10	Potentilla griffithii	Rosaceae	Vegetative
September (autumn)	n  = 55 different vascular plant species (n = 25 sampling plots)
	>30	Kobresia nepalensis	Cyperaceae	Vegetative
		Poa himalayana	Poaceae	Flowering
	20–30	Ranunculus hirtellus	Ranunculaceae	Fruiting
	10–20	Potentilla griffithii	Rosaceae	Fruiting
	0- 10	Bistorta vivipara	Polygonaceae	Flowering and fruiting

Herbage botanical composition

The effect of season was highly significant on the total dry-weight content of the pasture. The herbs (forbs) were significantly higher in July but declined to 30% in September, which was the opposite of the contribution of grasses and cyperoids. Details of the aboveground herbage mass and the contribution of the botanical groups are presented in Table 3.

Table 3. Above-ground herbage dry mass harvested from the experimental pasture site over two different seasons of grazing at 4200 m above sea level in the Kanchenjunga Conservation Area of Nepal.

	^bMonths of measurements		^cSEM	p-value
^aFunctional groups	July (Summer)	September (Autumn)
Herbage mass
Total herbage dry mass, t ha^−1	2600^d	2000^e	180	<0.01
Botanical groups
Grasses (%)	32^e	38^d	7.5	<0.001
Cyperus (%)	26^e	31^d	4.2	<0.05
Herbs (%)	40^d	30^e	5.3	<0.001
Herbage chemical composition
OM	90	82	–	–
CP	22	19.5	–	–
NDF	50	60	–	–
ADF	36.5	35.4	–	–
ADL	12	15	–	–
^fHemicellulose	13.5	24.6	–	–
^gCellulose	24.5	20.4	–	–

^aMeans within the same row without a common superscript differ significantly (p < 0.05).

^bMonths of measurements indicate summer and autumn seasons.

^cSEM = standard error of mean. OM = organic matter, CP = crude protein, NDF = Neutral Detergent Fibre, ADF = Acid Detergent Fibre, ADL = Acid Detergent Lignin.

^fHemicellulose = NDF-ADF

^gCellulose = ADF-ADL

Herbage chemical composition

The organic matter and CP content declined from July to September. In contrast to the measurements made in July, the coarseness (fibrous residues) was higher in September, unless the cellulose content was lower (Table 3).

Body weight gain

Both season and parity had a significant effect (p < 0.05) on the body weight of lactating hybrids (Table 4). In September, the initial body weight was the highest in 6th parity hybrids and daily weight gain in the 4th and 6th parity hybrids was more rapid than that of the youngest parity hybrids (2nd parity). In general, parity had a similar effect on the daily weight gain of the lactating hybrids, but the effect of grazing season remained significant (p < 0.05).

Table 4. Body weight gain and milk yield of the three parity groups of cattle × yak hybrids over two different seasons of grazing at 4200 m above sea level in the Kanchenjunga Conservation Area of Nepal.

Parameters	Season	Parity groups			^1SEM	p-values
		2nd	4th	6th		Season (S)	Parity(Pa)	S × Pa
Body weight
Initial body weight, kg	July (Summer)	232^e	248^c,d	260^b,c	3.05	<0.001	<0.001	0.153
	September (Autumn)	236^d,e	263^a,b	274^a
^2Daily weight gain, kg day^−1	Aug.-July	0.60^a	0.34^a,b	^−0.09^b,c	0.06	0.041	0.068	<0.001
	Sept.-Aug.	^−0.46^c	0.17^b	0.55^a,b
Milk yield
Absolute milk yield, kg day^−1	July (Summer)	2.15^b,c,d	2.70^a,b	3.42^a	0.17	<0.001	<0.001	<0.01
	September (Autumn)	1.46^d	2.44^b,c	1.81^c,d
^3ECM, kg day^−1	July (Summer)	2.56^c,d	3.58^b,c	4.78^a	0.24	<0.001	<0.001	<0.001
	September (Autumn)	2.03^d	3.67^b	2.54^c,d
Milk composition
Fat %	July (Summer)	5.60^d	6.79^c	7.40^b	0.14	<0.001	<0.001	<0.001
	September (Autumn)	7.50^b	8.30^a	7.50^b
Protein %	July (Summer)	3.36	3.35	3.24	0.04	0.020	0.226	0.206
	September (Autumn)	3.19	3.27	3.23
Lactose %	July (Summer)	4.72	4.73	4.56	0.06	0.013	0.217	0.201
	September (Autumn)	4.48	4.59	4.55

¹Pooled SEM across the months and parity groups. Months represents the summer and autumn seasons in the local transhumance system.

²Body measurements done only at the start of data collection in July (arithmetic mean and SEM presented). First 30 days daily weight change = body weight in August minus body weight in July; and second 30 days weight change= body weight in September minus body weight in August.

³ECM calculated following ALP (2013).

Milk yield and composition

Daily milk yield, ECM, and fat content were significantly affected (p < 0.05) by season, parity, and their interaction (Table 4). The highest daily milk yield was obtained from 6th parity hybrids (3.42 kg day⁻¹) in July and the lowest was obtained from 2nd parity groups in September (1.5 kg day⁻¹). The daily milk yield of 4th parity lactating hybrids was similar in July and September (2.70 vs. 2.44 kg day⁻¹) There was also a similar trend in energy-corrected milk yield.

Milk fat content was highest in September (8.30%) in the 4th parity hybrids (Table 4). Milk protein and lactose content were significantly higher (p < 0.05) in July than in September, due to advancing lactation and changes in the growth stages of the herbages (Table 2). The daily output of fat (185.10 g in July vs. 149.37 g in September), protein (91.03 g vs. 61.60 g), and lactose were significantly affected (p < 0.05) by season, parity, and their interaction (data not shown).

Discussion

Effect on daily weight gain

In the present study, both parity and month of grazing had a significant effect on the body weight gain of lactating cattle × yak hybrids. The differences in daily weight gain between the different parity groups might be associated with the physiological adjustments to milk production performance. Daily body weight gain is an indicator of the energy supply (Long et al. 1999) that comes from the herbages. The highest body weight gain in the 6th parity group could be due to the fact that the animals reached their adult size and optimum body metabolism, leading to greater daily body weight gain, provided that enough forage was available from July to September. There is sometimes a decline of up to one-third of the body weight of Chinese yaks during winter (Xue et al. 2005). Whilst the higher daily weight gain in 4th and 6th parity animals than that of young animals would be due to optimum body metabolism, resulting in low energy partition for a thermoregulatory mechanism (Khan et al. 1992). It might also be possible that young animals do not have optimum digestibility of forage compared to that of adults. As expected, the body weight gain during the first month of observation was higher than that in the second month. This could be due to the fact that there was optimum good quality herbage available during the experimental observation in July, and the forage quality might have degraded or matured in September, resulting in low body weight gain in the latter case.

Effect on milk yield and milk components

The highest daily milk yield and energy-corrected milk (ECM) was found in the 6th parity lactating hybrids in July, which could have been due to the quality of herbage and the effect of lactation stage, as reported previously by Gyamtsho (2000). In contrast, low milk yield in the 2nd parity group could be due to animal-related factors, i.e. animals in the 2nd parity group had not reached full production potential by that time, due to age-related phenomena. Milk fat content gradually increased from July to September whereas lactose and protein content gradually decreased. The higher milk fat content in September than in July could be due to the advancing stage of lactation and increased fibre content of the herbage. When lactation stage advances, milk yield declines, and the milk constituents increase (Ostersen et al. 1997). The stage of lactation, together with the changing pasture quality, would probably provide the best reasons why milk yield declined more during the measurements in September and contrast, had the highest milk fat content. Here, the trend of higher milk fat content in September was in agreement with the physiological changes in milk-producing hybrids with alteration in forage chemical composition and the fibre content of the diet (Leiber et al. 2006; Ferlay et al. 2006). The higher protein and lactose content in July milk were probably due to surplus high-quality forage compared to that in September, when the herbages in Himalayan alpine pastures start to mature and ultimately fade away.

Purebred yaks are efficient in fibrous feed utilization (Bao et al. 2011) whilst it is expected that their hybrids with cattle might also have gained such genetic merit. Here, the higher milk protein and lactose content in July is corroborated by the fact that, by that time, forage had optimal growth with low fibre content i.e. high propionic acid production from rumen fermentation which is utilized directly for lactose and protein synthesis (Storry and Sutton 1969).

The decrease in milk protein content in September further indicated a severe shortage in energy and protein supply by the herbage (Brun-Lafleur et al. 2010), which showed the reduced requirements for the formation of these milk constituents because of the progressing stage of lactation (Rook and Line 1961). During September, animals might have gone through severe energy and protein supply shortages, which might have reduced the formation of milk constituents as energy and protein partitioning is the lowest priority for such productive traits e.g. milk production during the period of nutrient deficiency. In the present study site, alpine pastures reach maturity in September, with high fibre content that probably resulted in relatively high rumen acetate concentrations, which could be the reason for the higher milk fat content in milk of any parity groups. The variation found in milk yield and energy-corrected milk (ECM) could be attributed to variation in the quality and quantity of the available forage, and interaction between parity and forage quality. The decline in milk yield, rapid body weight gain in 6th parity groups, and significant weight loss and low milk yield in 2nd parity hybrids are indicative of rapid changes in body reserves (Rook 1976) for production in lactating hybrids that are either too young (2nd parity) or too old (6th parity). It would further indicate that older parity hybrids are adapted to lower quality herbage intake than the younger lactating hybrids (2nd parity). Results of a cattle experiment by Amasaib et al. (2011) indicated that parity affects the total milk yield. In the present study, milk fat content was also found significantly affected by parity and grazing season and could be associated with the lactation length, which cannot be excluded from the measured milk-related parameters. The measurement period in July is the peak milk yielding season for hybrids and from then onwards, milk yield declines and the fat content in milk increases.

Conclusions

This experiment carried out in the eastern Himalaya of Nepal revealed that cattle × yak hybrids with older parities (4th parities) would be more promising for commercial herding than younger parities (2nd parity), as shown by their persistently higher daily milk yield and daily outputs of milk constituents in two different grazing seasons. The findings can further document the performance of cattle × yak hybrids and suggest the optimal selection of lactating hybrids for commercial herding in the Himalayan alpine rangelands setting at least at 4th parity. Moreover, the heterotic potential in milk yield and composition is yet to be determined for cattle × yak hybrids grazing in the transhumance system. A detailed rangeland inventory and grazing behaviour studies are needed to confirm the findings of the present study.

Disclosure statement

No potential conflict of interest was reported by the author.

ORCID

Shanker Raj Barsila http://orcid.org/0000-0001-6840-1503

Additional information

Funding

This work was supported by Directorate of Research and Extension of the Agriculture and Forestry University, Nepal.