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Seasonal Effects on Milk Components

Seasonal Effects on Milk Components

Seasonal Effects on Milk Components

Summer has arrived! The days are getting longer and the temperature is rising. However, you may now begin to notice the not so pleasant part of summer: a decline in milk components. The graph below highlights a very repeatable seasonal pattern of observations in milk fat and protein concentrations as seen over a ten-year period of time in the Mid-East Milk Order. Milk fat and protein concentrations peak in the winter months and fall to their lowest point around July and August.Impact of Heat Stress on Milk Yield and Milk FatHeat stressed animals may have lower levels of blood protein and energy due to the in-efficiencies of rumination and metabolism during this heat challenge. Both blood protein and energy levels can influence milk and milk fat yields. Cows tend to slug feed during cooler periods of the day so as not to increase heat of digestion. Slug feeding can result in periods of ruminal acidosis, which can decrease milk fat content. Additionally, highly fermentable diets (more starch and sugar) are commonly fed to dairy cows to maximize energy intake and increase the ease of substrate breakdown in the rumen. This can result in a rapid production of energy favoring volatile fatty acids after consumption which reduces ruminal pH and can depress fiber digestion and ultimately cause milk fat depression (Harvatine, 2012).Heat Stress and Milk ProteinRecently, a trial was conducted in Australia to determine the impact of heat stress on milk protein content (Cowley et al., 2014). Dry matter intake of cows in a heat stressed environment was monitored, and a control group of cows in a thermal neutral climate were fed the same ration at the same level of intake. The heat stressed animals had lower milk protein content than did the animals with similar DMI in a thermal neutral climate. What could be happening? Amino acids (AA) are the building blocks of protein, and in normal conditions, the cow prefers to use AA for protein production. During periods of heat stress, the cow may be using more amino acids for energy production to meet additional requirements. Therefore, fewer AA may be available for milk protein production.Nutritional strategies to improve milk components in the summer:Strategy BenefitIncrease sodium bicarbonate (8 ounces) Improves rumen buffering capacityFeed more digestible forages to high producing cows Reduces heat of digestionIncrease fat content of ration with rumen inert fat Improves energy supplyFeed higher metabolizable protein diets Matches increased AA supply with demandBalance ration for lysine and methionine Improves efficiency of use of total dietary proteinDon’t feed excess RDP Energy is wasted to metabolize excess RDP

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