MACROMINERAL REQUIREMENTS FOR MAINTENANCE, BODY WEIGHT GAIN AND PREGNANCY OF DAIRY COWS

RESUMO

sendo o primeiro subgrupo submetido ao manejo alimentar ad libitum e o segundo subgrupo ao manejo nutricional de manutenção. As vacas gestantes foram submetidas a técnica de abate comparativo ao longo de quatro tempos de gestação distintos 140, 200, 240 e 270 dias, assim como as vacas abertas foram abatidas nos dias 200, 240 e 270 de gestação do grupo prenhe. Sete períodos de 28 dias foram realizados para digestibilidade total do trato. As necessidades líquidas de manutenção, crescimento e gestação foram estimadas, bem como o coeficiente de retenção e a eficiência do uso de macrominerais para a gestação. Na necessidade líquida de manutenção, não houve diferença entre vacas abertas e gestantes para todos os macrominerais. As necessidades líquidas de cálcio, fósforo, sódio, potássio, magnésio e enxofre foram 13,48, 8,35, 10,08, 45,89, 4,44 e 7.82 mg / kg de peso corporal vazio (PCVZ), respectivamente. Além disso, o coeficiente retido para cálcio, fósforo, sódio, potássio e magnésio foram 65%, 74%, 43%, 56%, 42% e 85%, respectivamente. A exigência líquida de ganho mostrou diferenças estatísticas entre vacas gestantes e vacas abertas para cálcio, fósforo e enxofre. No entanto, sódio, potássio e magnésio não apresentaram diferenças para ganho entre vacas gestantes e não gestantesPara gestação, as seguintes predições foram proposta para Ca ; para P ; para Na , K foi , predição para magnésio foi e para S Como conclusões, as exigências de macrominerais para ganho e, consequentemente a dietética, devem ser considerados separadamente para vacas prenhas e vazias. Além disso, as exigências de macrominerais para gestação mostraram a predição da exigência de vacas gestantes deve ser formulada considerando o comportamento exponencial de retenção de macrominerais ao longo da gestação Palavras-chave Girolando, Gestação, Gado leiteiro, Exigências nutricionais, Modelos matemáticos

ABSTRACT

Macrominerals are essential to maintain healthy, high reproductive efficiency and milk production of dairy cattle. Although understanding the macromineral requirements are essential to meet the needs of cows accurately, studies to predict macromineral requirements throughout the gestation of dairy cows are scarce. Thus, the goal of the present study was to set approaches to predict the macromineral requirements of crossbred Holstein x Gyr cows throughout the gestation. Sixty-two Holstein-Gyr crossbred cows were enrolled in this experiment. Randomly, the cows were divided 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. The pregnant cows were slaughtered throughout four different days of gestation 140, 200, 240, and 270 days, and the open cows were slaughtered at day 200, 240, and 270 of gestation following the pregnant group. Seven periods of 28 days were accomplished for total tract digestibility. Macrominerals were analyzed by specific methods as each one needs to be quantified. Net requirements for maintenance, growth, and gestation were estimated as well as the retention coefficient and efficiency to use macrominerals for gestation. On the net requirement for maintenance, there was not difference between open and pregnant cows for all macrominerals. 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, phosphorus and sulfur. On the other hand, sodium, potassium, and magnesium did not present differences for gain between pregnant and non-pregnant cows. The macromineral requirements for gestation were set for each mineral by exponential equations. The predicting model for calcium was . For phosphorus, the model was . On sodium the equation was . For potassium, the model for pregnancy was . The magnesium model for pregnancy was and sulfur for pregnancy was . In conclusion, the macromineral requirements for gain and dietary should be considered carefully for each mineral for pregnancy status for cows. Additionally, the exponential macromineral requirement throughout pregnancy should be considered in diet formulation for pregnant cows. Keyword Girolando, Pregnancy, Dairy cattle, Nutrient requirements, Mathematical modeling