Macromineral requirements for maintenance, body weight gain and pregnancy of daiy cows
Authors:   , Nova Carlos Henrique Paiva 
Published: September 2024

Macrominerals are essential to maintain healthy, high reproductive efficiency and performance of dairy cattle. Based on it, understanding the macromineral requirements are crucial to formulate diets to meet the needs of cows accurately. However, studies to predict macromineral requirements for pregnant dairy cows are scarce. Thus, the goal of this study was to set approaches to predict the macromineral requirements of pregnant crossbred Holstein x Gyr cows. 62 Holstein-Gyr crossbred cows were enrolled in this experiment. The cows were sorted into 3 different groups: pregnant, open, and reference cows. Two subgroups were formed both for pregnant and open cow groups, where, the first subgroup was submitted to ad libitum feed management and the second subgroup was submitted to the maintenance nutritional management (feed intake equals 1.15% of body weight). The pregnant cows were harvested at four different days of gestation: 140, 200, 240, and 270 days, as well as the open cows, were harvested at day 200, 240, and 270 of gestation of the pregnant group. Seven periods of 28 days were accomplished for total tract digestibility (122, 150, 178, 206, 234, and 262 days of gestation). Net requirements for maintenance, growth, and gestation were estimated as well as the retention coefficient and efficiency to use macrominerals for gestation. The net requirement for calcium, phosphorus, sodium, potassium, and magnesium were 13.4837, 8.3534, 10.0751, 45.8889, and 4.4436 mg/kg of empty body weight (EBW), respectively. Additionally, the retained coefficient for calcium, phosphorus, sodium, potassium, and magnesium were 0.6516, 0.7402, 0.4267, 0.5641 and 0.4211, respectively. The net requirement for gain showed statistical differences between pregnant and open cows for calcium and phosphorus. On the other hand, sodium, potassium, and magnesium did not present differences for gain between pregnant and non-pregnant cows. For calcium, the predicting models of gain for non-pregnant cows and pregnant cows were 𝐶𝑎 (𝑔/𝑑) = 0.2818 × 𝐸𝐵𝑊 0.6202 × 𝐸𝐵𝐺 and 𝐶𝑎 (𝑔/𝑑) = 3.1319 × 𝐸𝐵𝑊 0.1484 × 𝐸𝐵𝐺, respectively. For phosphorus, the models of gain for open and pregnant cows 𝑔 were 𝑃 ( ) = 0.7669 × 𝐸𝐵𝑊 0.3843 × 𝐸𝐵𝐺 𝑑 and 𝑃 (𝑔/𝑑) = 2.4456 × 𝐸𝐵𝑊 0.1435 × 𝐸𝐵𝐺, respectively. The predicting models of gain for sodium were 𝑁𝑎 (𝑔/𝑑) = 0.0201 × 𝐸𝐵𝑊 0.7219 × 𝐸𝐵𝐺 and 𝑁𝑎 (𝑔/𝑑) = 0.1597 × 𝐸𝐵𝑊 0.3185 × 𝐸𝐵𝐺 for open and pregnant cows, respectively. For potassium, the models of potassium for open cows were 𝐾 (𝑔/𝑑) = 0.2178 × 𝐸𝐵𝑊 0.3514 ×𝐸𝐵𝐺 and for pregnant cows was 𝐾 (𝑔/𝑑) = 0.7269 × 𝐸𝐵𝑊 0.1191 × 𝐸𝐵𝐺. About magnesium requirement for gain, the model for open cows was 𝑀𝑔 (𝑔/𝑑) = 0.0508 × 𝐸𝐵𝑊 0.4163 × 𝐸𝐵𝐺 and for pregnant cows was 𝑀𝑔 (𝑔/𝑑) = 0.6170 × 𝐸𝐵𝑊 −0.0700 × 𝐸𝐵𝐺 . Predictions for gain for sulfur for non-pregnant and pregnant cows were 𝑁𝑒𝑡 𝑆𝑔𝑎𝑖𝑛 = 0.1708 × 𝐸𝐵𝑊 0.5185 , and 𝑁𝑒𝑡 𝑆𝑔𝑎𝑖𝑛 = 1.2422 × 𝐸𝐵𝑊 0.1333 , respectively. For gestation, the predicting model for calcium was 𝐶𝑎 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/𝑑) = 0.0125 𝑒 0.02489 × 𝐷𝑃 . For phosphorus, the model was 𝑃 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/ 𝑑) = 0.0207 𝑒 0.02049 × 𝐷𝑃 . On sodium the equation was 𝑁𝑎 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/𝑑) = 0.0588 𝑒 0.0115 × 𝐷𝑃 . For potassium, the model for pregnancy was 𝐾 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/𝑑) = 0.0439 𝑒 (0.0119 × 𝐷𝑃) . The magnesium model for pregnancy was 𝑀𝑔 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/𝑑) = 0.0021 𝑒 (0.01748 × 𝐷𝑃) and sulfur for pregnancy was 𝑆 𝑟𝑒𝑞𝑝𝑟𝑒𝑔 (𝑔/𝑑) = 0.0263 𝑒 (0.0148 × 𝐷𝑃) . Keyword: Girolando, Pregnancy; Dairy cattle; Nutrient requirements; Mathematical modeling