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Calving difficulty incurred by 2-year-old heifers is a major problem. Research has shown the basic cause is a disproportion between the calf size at birth (birth weight) and the heifer's birth canal (pelvic area). Several factors affect calf birth weight. including genetics of sire and dam, dam nutrition, calf sex and climatic conditions. Weather conditions may have a significant effect on calf birth weight. When a pregnant animal is exposed to cold temperatures, blood is concentrated internally to maintain its core body temperature. Therefore. during prolonged periods of cold weather, the fetus may receive more nutrition because more blood flows to the uterus. Research has shown that blood flow is the primary determinant of nutrient uptake by the uterus.
Calf birth weights have been found to be heavier in northern climates than in southern climates. Research has also shown that calves born in summer and fall have lower birth weights with less calving difficulty than those born in late winter and early spring. The objective of this research was to determine how changes in climatic temperatures and wind chill during winter months influence calf birth weights in the spring.