| Over the past three decades,there has been a considerable increase in the global production of meat and dairy products derived from ruminant animals,with an increase of43% and 55%,respectively,which has resulted in nutrition being provided for approximately 10% of the global population.Grazing management is a significant contributor,accounting for over 40% of livestock production.With its vast expanse of grazing land,the Qinghai-Tibet Plateau is one of the largest areas on the planet.This region is responsible for producing over 90% of the dairy products and more than 50% of the meat products consumed by the local population,with the yak(Bos grunniens)being the primary livestock used.However,the improper grazing management of grassland has led to a spatial-temporal imbalance in the supply and demand of grass and livestock,resulting in grassland degradation and a vicious cycle.This is a global issue because the ecological environment of the Qinghai-Tibet Plateau is fragile,and the grass-livestock system is representative of similar systems around the world.However,there is a lack of research into whether the seasonal rotational grazing of yaks can enhance production potential by influencing grazing behavior,digestive metabolism,immune performance,and rumen microbial flora.In this study,we conducted research at the Maqu Grassland Agricultural Trail Station of Lanzhou University to investigate the effects of seasonal grazing on the behavior of yaks,their digestive metabolism,rumen microbial flora,and serum immune performance.The findings of the study are as follows:1.Seasonal dynamics of yak grazing behavior in an alpine meadowYaks exhibit similar daily grazing behavior patterns in different grazing seasons,generally characterized as feeding-rumination/resting-feeding,with the first peak of feeding occurring after turnout(8:00 AM),followed by rumination,and the second feeding peak reached before return to the corral(7:00 PM).During summer and autumn,the number of feeding bites per grazing event and the number of bites per step were significantly higher than that in winter and spring(P < 0.05),while the total walking distance was the opposite(P < 0.05).In the four grazing seasons of spring,summer,autumn,and winter on the Qinghai-Tibet Plateau’s high-altitude alpine meadows,the daily average grazing time,walking time,and rumination/resting time of yaks were 7.96-8.69 h/d,0.96-1.88 h/d,and 2.32-2.78 h/d,respectively.The highest grazing time was observed in autumn(8.69 h),the highest rumination time was in summer(2.43 h),and the highest walking time was in winter(1.88 h).The total number of grazing bites,total walking distance,and the number of bites per step were 11089-18020 bites/day,818-1108 steps/day,and 10-21bites/step,respectively,in the four seasons of spring,summer,autumn,and winter.The total walking distance of yaks was the highest in winter(1108 steps),and the total number of grazing bites was the highest in summer(18020 bites).Furthermore,a structural equation model showed that the grazing season explained 42.1% of the variance in yak grazing behavior,and that the season indirectly affects yak grazing behavior by influencing the nutritional quality of grass,vegetation community composition,and vegetation alpha diversity.2.Seasonal dynamics of digestion and metabolism of grazing yaks in an alpine meadowThe dry matter digestibility of yaks decreased in the order of spring,summer,autumn,and winter,with the highest dry matter digestibility observed in spring(79.24%),which was 5.09%,4.02%,and 8.19% higher than that in summer,autumn,and winter,respectively.The acid detergent fiber digestibility was highest in autumn(68.25%),significantly higher than that in spring and winter(P < 0.05),with increases of 6.14% and3.27% compared to spring and winter,respectively.The neutral detergent fiber digestibility in summer and autumn was significantly higher than that in spring and winter(P < 0.05),with increases of 6.05% and 5.36% compared to spring and winter,respectively.The crude protein digestibility was highest in spring(65.27%),followed by autumn,and lowest in winter,while the crude protein digestibility in summer was 10.98% higher than that in winter.The crude fat digestibility was highest in autumn(76.23%)and lowest in winter,with an increase of 6.18% compared to winter.Furthermore,a structural equation model showed that seasonal grazing explained 56.8% of the variance in yak digestion rates,and that seasonal grazing indirectly affects yak apparent digestion rates by influencing grass nutritional quality,dry matter intake,vegetation alpha diversity,and yak grazing behavior.3.Seasonal dynamics of rumen enzyme activity and rumen microflora in grazing yaks in an alpine meadowGrazing season have a significant impact on the enzymatic activity of the rumen microbiota in yaks.Rumen cellulase activity is significantly higher in winter than in spring,summer,and autumn(P < 0.05);rumen amylase activity is significantly higher in summer and autumn than in spring and winter(P < 0.05),while the trend of protease is opposite to that of amylase(P < 0.05).Grazing season have a significant impact on the diversity of rumen microbiota.Species richness(Chao 1)is significantly higher in spring than in the other three seasons(P < 0.05).Community structural diversity is significantly higher in summer than in the other three seasons(P < 0.05).The relative abundance of Bacteroidetes,Firmicutes,and Prevotella＿1 is highest in all four seasons,while the relative abundance of Firmicutes in summer is significantly higher than in the other three seasons(P < 0.05).In addition,the structural equation model shows that grazing season explain 69.5% of the variations in rumen enzyme activity and microbial composition in yaks.Grazing season can indirectly affect rumen enzyme activity and microbial composition in yaks through its impact on dry matter digestion rate,dry matter intake,grazing behavior,and energy metabolism.4.Seasonal dynamics of serum biochemical indices in yaksThe total cholesterol,total protein,albumin,aspartate aminotransferase activity,and alanine aminotransferase activity in yak serum showed an increasing trend in spring,summer,and autumn,followed by a decrease in winter,while the urea nitrogen content and alkaline phosphatase activity showed the opposite trend,with a higher level in winter and spring and a lower level in summer and autumn.In summer,the total cholesterol(24.55g/L)and albumin(2.24 mg/d L)levels were the highest,and in autumn,the total protein(66.35 g/L),aspartate aminotransferase activity(80.06 U/L),and alanine aminotransferase activity(18.19 U/L)were the highest.Furthermore,the contribution of seasonality for lipid and protein metabolism indicators in grazing yaks was 43.2% and 71.3%,respectively,as determined by structural equation modeling.Seasons can indirectly affect lipid metabolism indicators by affecting dry matter digestibility,feed intake,grazing behavior,and energy metabolism,while it can indirectly affect protein metabolism indicators by affecting nitrogen metabolism,feed intake,grazing behavior,and energy metabolism.5.The relationship between the grazing behavior,digestion and metabolism,rumen microbial community,rumen enzyme activity,and serum biochemical indices of yaks in alpine meadow.Using the framework of random matrix theory,we developed an ecological network model to investigate the interrelationships among grazing behavior,digestion and metabolism,rumen microbial community,rumen enzyme activity,and serum biochemical indices of yaks in different seasons of alpine meadows.Our model parameters reveal that the rumen microbial community exhibits lower connectivity in the network analysis graph,whereas digestion and metabolism as well as serum biochemical indices demonstrate higher connectivity.Notably,the model underscores the crucial role of interactions among these indicators in yak health.Consequently,adopting appropriate management strategies across the four grazing seasons can capitalize on the beneficial effects of summer grazing on yak’s digestion,metabolism,and immune performance while offsetting the negative impacts of other seasons to bolster productivity in the Qinghai-Tibetan Plateau.The fundamental data obtained from our research,in combination with further exploration of daily weight gain,meat and milk quality,and the health of grazing pastures,holds practical significance for the advancement of animal husbandry in the Tibetan region. |
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