Effects of warm season supplementary feeding on the milk performance of lactating yaks grazing on natural grassland in an alpine pastoral area

The alpine meadow grassland of the Qinghai-Tibet Plateau is known for its high nutritional quality, but its yield is extremely low. The lack of protein forage and grasslands show varying degrees of degradation, which have led to malnutrition among lactating yaks, resulting in a decline in both milk yield and quality. While succulent feed has been known to boost milk production in dairy cows due to its vitamin and water content, its effect on lactating yaks is unclear. Given that most pastoral areas in the region are arid with low water content in natural grasses, supplementing succulent feed may increase vitamin and water intake and improve lactation performance. To investigate this hypothesis, 24 lactating yaks with similar weight, age, and parity were selected from the Nagqu alpine pastoral area of Tibet during the 2021 (July–October) warm season and were randomly divided into four groups. The groups were fed protein Medicago sativa: 1 kg·(d·head)⁻¹, succulent Raphanus sativus: 1 kg·(d·head)⁻¹, protein + succulents 0.5 kg·(d·head)⁻¹ each of alfalfa and radish, and non-supplemented feed (control group) in addition to their traditional grazing in natural grassland. The study aimed to determine the effects of protein and succulent feed supplementation on the yield and quality of yak milk during lactation while grazing in the alpine pastoral area of the Qinghai-Tibet Plateau. Results showed that compared to the control, protein feed supplementation led to a significant 22% increase in daily milk yield and delayed the decline of milk production during lactation. In contrast, succulent feed supplementation reduced the daily milk yield by 6%. Protein feed alone or combined with succulent feed significantly increased milk protein percentage, non-fat solids percentage, lactose percentage, ash percentage, and density while reducing the milk freezing point. Additionally, only succulent feed significantly improved milk fat percentage, protein percentage, non-fat solids percentage, ash percentage, and reducing freezing point. However, the three supplementary feeding treatments had no significant effect on the body weight of lactating yaks and their calves. In summary, including during the warm season when the pasture is vigorous, natural grassland alone cannot meet the nutritional requirements of lactating yaks in the alpine meadow grassland of the Qinghai-Tibet Plateau. The supplementation of protein and succulent feed can effectively improve the milk production potential of lactating yaks, which is important to alleviate the contradiction between grass and livestock and accelerate local animal husbandry development to enhance living conditions.