Gestation

Pregnancy diagnosis is performed by manual palpation or ultrasound examination of the reproductive tract, or by analyzing blood or milk samples for hormone content. Manual tract manipulation should not be attempted before 50 days after breeding to prevent damage to the developing fetus. Once pregnancy is established in a disease-free animal the probability is high that it will be maintained to calving, but if excessive losses occur a disease or toxic nutritional problem (e.g., pine needle-induced abortion) should be suspected. Gestation is the physiological period during which the fetus develops and the dam prepares for a short postpartum interval (calving to first estrus) and successful rebreeding. All nutrient requirements must be met.[5] Body condition scores are used to determine adequacy of gestation management and rebreeding potential. Scores are visual or palpated estimates of body fleshing and fat cover of the dam. Numerical values are assigned, from 1=very thin and emaciated to 9=very fat.[3] Separating pregnant females into heifers, females with low condition scores, and females with high condition scores is excellent, because feeding levels can be adjusted critically and social competition minimized. The key condition score goal is a minimum 5 at calving, indicating gestation nutrient requirements for dam and fetus have been met. Calves from 5-score dams are more vigorous and less susceptible to disease than calves from lower-score dams. The 5 score indicates that body reserves are present to maintain the dam during the critical postpartum nutritional period, from calving until forage is adequate to maintain bodyweight in the lactating dam. Maintaining dams in condition scores higher than 7 is costly and results in increased dystocia. Nutrient requirements, feed intake, and digestibility are negatively affected by cold temperatures. In dams with a heavy winter hair coat, a 6°C decrease (includes chill factor) in temperature increases the metabolizable energy requirement for maintenance by approximately 8%. Physical activity (e.g., walking) increases nutrient requirements. High environmental temperatures reduce birth weights and the subsequent milk production and fertility of the dam.

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